change error code (#7790)

fix: sponsor test coverage

.cspell.config.yaml

@@ -279,6 +279,8 @@ words:
   - sles
   - soci
   - socidb
+  - sponsee
+  - sponsees
   - SRPMS
   - sslws
   - statsd
@@ -327,6 +329,7 @@ words:
   - unserviced
   - unshareable
   - unshares
+  - unsponsored
   - unsquelch
   - unsquelched
   - unsquelching

include/xrpl/basics/base_uint.h

@@ -595,7 +595,7 @@ template <std::size_t Bits, typename Tag>
 [[nodiscard]] constexpr bool
 operator==(BaseUInt<Bits, Tag> const& lhs, BaseUInt<Bits, Tag> const& rhs)
 {
-    return (lhs <=> rhs) == 0;
+    return (lhs <=> rhs) == 0;  // NOLINT(modernize-use-nullptr)
 }
 
 //------------------------------------------------------------------------------

include/xrpl/ledger/ApplyView.h

@@ -3,6 +3,7 @@
 #include <xrpl/basics/base_uint.h>
 #include <xrpl/basics/safe_cast.h>
 #include <xrpl/beast/utility/instrumentation.h>
+#include <xrpl/ledger/OwnerCounts.h>
 #include <xrpl/ledger/ReadView.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Issue.h>  // IWYU pragma: keep
@@ -11,6 +12,7 @@
 #include <xrpl/protocol/MPTIssue.h>
 #include <xrpl/protocol/STAmount.h>
 #include <xrpl/protocol/STLedgerEntry.h>
+#include <xrpl/protocol/STTx.h>
 #include <xrpl/protocol/STVector256.h>
 
 #include <cstdint>
@@ -288,7 +290,7 @@ public:
     // Called when the owner count changes
     // This is required to support PaymentSandbox
     virtual void
-    adjustOwnerCountHook(AccountID const& account, std::uint32_t cur, std::uint32_t next)
+    adjustOwnerCountHook(AccountID const& account, OwnerCounts const& cur, OwnerCounts const& next)
     {
     }
 
@@ -411,6 +413,23 @@ public:
     emptyDirDelete(Keylet const& directory);
 };
 
+/** Bundles the mutable ledger view and the transaction being applied.
+
+    Passed together to avoid threading two separate parameters through every
+    helper that needs both the view (for state reads/writes) and the
+    transaction (for field inspection and metadata).
+
+    Both members are non-owning references; the caller is responsible for
+    ensuring that the referenced objects outlive the ApplyViewContext.
+
+    TODO: replace with ApplyContext after it's untangled with xrpl/tx
+*/
+struct ApplyViewContext
+{
+    ApplyView& view;
+    STTx const& tx;
+};
+
 namespace directory {
 /** Helper functions for managing low-level directory operations.
     These are not part of the ApplyView interface.

include/xrpl/ledger/OwnerCounts.h

@@ -0,0 +1,70 @@
+#pragma once
+
+#include <xrpl/beast/utility/instrumentation.h>
+#include <xrpl/protocol/LedgerFormats.h>
+#include <xrpl/protocol/SField.h>
+#include <xrpl/protocol/STInteger.h>  // IWYU pragma: keep
+#include <xrpl/protocol/STLedgerEntry.h>
+
+#include <cstdint>
+#include <limits>
+
+namespace xrpl {
+
+struct OwnerCounts
+{
+    std::uint32_t owner = 0;
+    std::uint32_t sponsored = 0;
+    std::uint32_t sponsoring = 0;
+
+    OwnerCounts() = default;
+    OwnerCounts(SLE::const_ref sle)
+        : owner(sle->at(sfOwnerCount))
+        , sponsored(sle->at(sfSponsoredOwnerCount))
+        , sponsoring(sle->at(sfSponsoringOwnerCount))
+    {
+        XRPL_ASSERT(
+            owner >= sponsored,
+            "xrpl::OwnerCounts : OwnerCount must be greater than or equal to "
+            "SponsoredOwnerCount");
+        XRPL_ASSERT(sle->getType() == ltACCOUNT_ROOT, "xrpl::OwnerCounts : sle is AccountRoot");
+    }
+
+    [[nodiscard]] std::uint32_t
+    count() const
+    {
+        std::int64_t const x = static_cast<std::int64_t>(owner) - sponsored + sponsoring;
+        if (x < 0)
+        {
+            // LCOV_EXCL_START
+            UNREACHABLE("xrpl::OwnerCounts::count : count less than zero");
+            return 0;
+            // LCOV_EXCL_STOP
+        }
+
+        if (x > std::numeric_limits<std::uint32_t>::max())
+            return std::numeric_limits<std::uint32_t>::max();  // LCOV_EXCL_LINE
+        return static_cast<std::uint32_t>(x);
+    }
+
+    auto
+    operator<=>(OwnerCounts const& o) const
+    {
+        if (auto cmp = count() <=> o.count(); cmp != 0)  // NOLINT(modernize-use-nullptr)
+            return cmp;
+        if (auto cmp = owner <=> o.owner; cmp != 0)  // NOLINT(modernize-use-nullptr)
+            return cmp;
+        if (auto cmp = sponsored <=> o.sponsored; cmp != 0)  // NOLINT(modernize-use-nullptr)
+            return cmp;
+        return sponsoring <=> o.sponsoring;
+    }
+
+    bool
+    operator==(OwnerCounts const& o) const
+    {
+        return this == &o ||
+            (owner == o.owner && sponsored == o.sponsored && sponsoring == o.sponsoring);
+    }
+};
+
+}  // namespace xrpl

include/xrpl/ledger/PaymentSandbox.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <xrpl/ledger/ApplyView.h>
+#include <xrpl/ledger/OwnerCounts.h>
 #include <xrpl/ledger/RawView.h>
 #include <xrpl/ledger/ReadView.h>
 #include <xrpl/ledger/detail/ApplyViewBase.h>
@@ -107,12 +108,12 @@ public:
     issuerSelfDebitMPT(MPTIssue const& issue, std::uint64_t amount, std::int64_t origBalance);
 
     void
-    ownerCount(AccountID const& id, std::uint32_t cur, std::uint32_t next);
+    ownerCount(AccountID const& id, OwnerCounts const& cur, OwnerCounts const& next);
 
     // Get the adjusted owner count. Since DeferredCredits is meant to be used
     // in payments, and payments only decrease owner counts, return the max
     // remembered owner count.
-    [[nodiscard]] std::optional<std::uint32_t>
+    [[nodiscard]] std::optional<OwnerCounts>
     ownerCount(AccountID const& id) const;
 
     void
@@ -124,7 +125,7 @@ private:
 
     std::map<KeyIOU, ValueIOU> creditsIOU_;
     std::map<MPTID, IssuerValueMPT> creditsMPT_;
-    std::map<AccountID, std::uint32_t> ownerCounts_;
+    std::map<AccountID, OwnerCounts> ownerCounts_;
 };
 
 }  // namespace detail
@@ -218,10 +219,11 @@ public:
         override;
 
     void
-    adjustOwnerCountHook(AccountID const& account, std::uint32_t cur, std::uint32_t next) override;
+    adjustOwnerCountHook(AccountID const& account, OwnerCounts const& cur, OwnerCounts const& next)
+        override;
 
-    [[nodiscard]] std::uint32_t
-    ownerCountHook(AccountID const& account, std::uint32_t count) const override;
+    [[nodiscard]] OwnerCounts
+    ownerCountHook(AccountID const& account, OwnerCounts const& count) const override;
 
     /** Apply changes to base view.
 

include/xrpl/ledger/ReadView.h

@@ -4,6 +4,7 @@
 #include <xrpl/basics/chrono.h>
 #include <xrpl/beast/hash/uhash.h>
 #include <xrpl/beast/utility/instrumentation.h>
+#include <xrpl/ledger/OwnerCounts.h>
 #include <xrpl/ledger/detail/ReadViewFwdRange.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Fees.h>
@@ -13,6 +14,7 @@
 #include <xrpl/protocol/MPTIssue.h>
 #include <xrpl/protocol/Protocol.h>
 #include <xrpl/protocol/Rules.h>
+#include <xrpl/protocol/SField.h>
 #include <xrpl/protocol/STAmount.h>
 #include <xrpl/protocol/STLedgerEntry.h>
 #include <xrpl/protocol/STObject.h>
@@ -189,8 +191,8 @@ public:
     // changes that accounts make during a payment. `ownerCountHook` adjusts the
     // ownerCount so it returns the max value of the ownerCount so far.
     // This is required to support PaymentSandbox.
-    [[nodiscard]] virtual std::uint32_t
-    ownerCountHook(AccountID const& account, std::uint32_t count) const
+    [[nodiscard]] virtual OwnerCounts
+    ownerCountHook(AccountID const& account, OwnerCounts const& count) const
     {
         return count;
     }

include/xrpl/ledger/View.h

@@ -210,8 +210,7 @@ canWithdraw(ReadView const& view, STTx const& tx);
 
 [[nodiscard]] TER
 doWithdraw(
-    ApplyView& view,
-    STTx const& tx,
+    ApplyViewContext ctx,
     AccountID const& senderAcct,
     AccountID const& dstAcct,
     AccountID const& sourceAcct,

include/xrpl/ledger/helpers/AccountRootHelpers.h

@@ -14,6 +14,7 @@
 
 #include <cstdint>
 #include <expected>
+#include <optional>
 #include <set>
 #include <vector>
 
@@ -26,21 +27,293 @@ namespace xrpl {
 [[nodiscard]] bool
 isGlobalFrozen(ReadView const& view, AccountID const& issuer);
 
-// Calculate liquid XRP balance for an account.
-// This function may be used to calculate the amount of XRP that
-// the holder is able to freely spend. It subtracts reserve requirements.
-//
-// ownerCountAdj adjusts the owner count in case the caller calculates
-// before ledger entries are added or removed. Positive to add, negative
-// to subtract.
-//
-// @param ownerCountAdj positive to add to count, negative to reduce count.
+/** Calculate liquid XRP balance for an account.
+ *
+ *  This function may be used to calculate the amount of XRP that
+ *  the holder is able to freely spend. It subtracts reserve requirements.
+ *
+ *  ownerCountAdj adjusts the owner count in case the caller calculates
+ *  before ledger entries are added or removed. Positive to add, negative
+ *  to subtract.
+ *
+ *  @param view The ledger view to read from
+ *  @param id The account ID to check
+ *  @param ownerCountAdj Positive to add to count, negative to reduce count
+ *  @param j Journal for logging
+ *  @return The liquid XRP amount available to the account
+ */
 [[nodiscard]] XRPAmount
 xrpLiquid(ReadView const& view, AccountID const& id, std::int32_t ownerCountAdj, beast::Journal j);
 
-/** Adjust the owner count up or down. */
+struct Adjustment
+{
+    std::int32_t ownerCountDelta = 0;
+    std::int32_t accountCountDelta = 0;
+};
+
+/** Returns the account reserve, in drops.
+ *
+ *  Actual owner count can be adjusted by delta in ownerCountAdj
+ *  Actual reserve count can be adjusted by delta in accountCountAdj
+ *  The reserve is calculated as:
+ *  (ownerCount + "sponsoring object count" - "sponsored object count" + additionalOwnerCount) *
+ *  increment + (1 if not sponsored account + sponsoringAccountCount) * "reserve base"
+ *
+ *  @param view The ledger view to read from
+ *  @param sle The ledger entry for the account
+ *  @param j Journal for logging
+ *  @param adj Adjustment to the owner/account count (default: 0/0). Positive to add, negative to
+ * subtract.
+ *  @return The account reserve amount in drops
+ */
+[[nodiscard]] XRPAmount
+accountReserve(ReadView const& view, SLE::const_ref sle, beast::Journal j, Adjustment adj = {});
+
+/** Convenience overload that accepts AccountID instead of SLE.
+ *
+ *  @param view The ledger view to read from
+ *  @param id The account ID
+ *  @param j Journal for logging
+ *  @param adj Adjustment to the owner/account count (default: 0/0). Positive to add, negative to
+ * subtract.
+ *  @return The account reserve amount in drops
+ */
+[[nodiscard]] inline XRPAmount
+accountReserve(ReadView const& view, AccountID const& id, beast::Journal j, Adjustment adj = {})
+{
+    return accountReserve(view, view.read(keylet::account(id)), j, adj);
+}
+
+/** Check if an account has sufficient reserve.
+ *
+ *  @param view The ledger view to read from
+ *  @param tx The transaction being processed
+ *  @param accSle The account's ledger entry
+ *  @param accBalance The account's balance
+ *  @param sponsorSle The sponsor's ledger entry (if applicable)
+ *  @param adj Adjustment to the owner/account count (default: 0/0). Positive to add, negative to
+ * subtract.
+ *  @param j Journal for logging (default: null sink)
+ *  @param insufReserveCode The transaction result code to return if the reserve is insufficient
+ *  (default: tecINSUFFICIENT_RESERVE).
+ *  @return Transaction result code
+ */
+[[nodiscard]] TER
+checkReserve(
+    ApplyViewContext ctx,
+    SLE::const_ref accSle,
+    XRPAmount accBalance,
+    SLE::const_ref sponsorSle,
+    Adjustment adj,
+    beast::Journal j,
+    TER insufReserveCode = tecINSUFFICIENT_RESERVE);
+
+/** Check if an account has sufficient reserve, deriving the sponsor internally.
+ *
+ *  Equivalent to the overload above, but resolves the sponsor via
+ *  getEffectiveTxReserveSponsor(ctx, accSle) instead of taking it explicitly. Use this
+ *  in the common case where the sponsor is simply the transaction's reserve
+ *  sponsor for accSle. Callers that must force the account's-own-reserve branch
+ *  (passing a null sponsor) or supply a different sponsor should use the
+ *  explicit overload above.
+ *
+ *  @param ctx The apply-view context (view + tx)
+ *  @param accSle The account's ledger entry
+ *  @param accBalance The account's balance
+ *  @param adj Reserve adjustments (owner/account count deltas)
+ *  @param j Journal for logging (default: null sink)
+ *  @return Transaction result code
+ */
+[[nodiscard]] TER
+checkReserve(
+    ApplyViewContext ctx,
+    SLE::const_ref accSle,
+    XRPAmount accBalance,
+    Adjustment adj,
+    beast::Journal j = beast::Journal{beast::Journal::getNullSink()});
+
+/** Return number of the objects which reserve is covered by the account(sle) (so called "owner
+ *  count"). Actual owner count can be adjusted by delta in ownerCountAdj.
+ *
+ *  @param sle The account's ledger entry
+ *  @param j Journal for logging
+ *  @param ownerCountAdj Adjustment to the owner count (default: 0)
+ *  @return The adjusted owner count
+ */
+std::uint32_t
+ownerCount(SLE::const_ref sle, beast::Journal j, std::int32_t ownerCountAdj = 0);
+
+/** Increase owner-count fields when the caller supplies the sponsor.
+ *
+ *  This helper does not create a ledger object. It updates reserve accounting
+ *  after the caller has created/updated an object.
+ *  If sponsorSle is provided, this also adjusts the account's sponsored count
+ *  and the sponsor's sponsoring count.
+ *
+ *  @param view The apply view for making changes
+ *  @param accountSle The account's ledger entry
+ *  @param sponsorSle The sponsor's ledger entry (if applicable)
+ *  @param count Amount to add to the owner count
+ *  @param j Journal for logging
+ */
 void
-adjustOwnerCount(ApplyView& view, SLE::ref sle, std::int32_t amount, beast::Journal j);
+increaseOwnerCount(
+    ApplyView& view,
+    SLE::ref accountSle,
+    SLE::ref sponsorSle,
+    std::uint32_t count,
+    beast::Journal j);
+
+/** Increase owner-count fields, deriving the tx reserve sponsor internally.
+ *
+ *  Equivalent to the overload above, but resolves the sponsor via
+ *  getEffectiveTxReserveSponsor(ctx, accountSle) instead of taking it explicitly. Use
+ *  this when the sponsor is the transaction's reserve sponsor for accountSle
+ *  (the common create path). Deletion paths, which derive the sponsor from an
+ *  object's sfSponsor field, should keep using the explicit overload.
+ *
+ *  @param ctx The apply-view context (view + tx)
+ *  @param accountSle The account's ledger entry
+ *  @param count Amount to add to the owner count
+ *  @param j Journal for logging
+ */
+void
+increaseOwnerCount(
+    ApplyViewContext ctx,
+    SLE::ref accountSle,
+    std::uint32_t count,
+    beast::Journal j);
+
+/** Convenience overload that accepts AccountID instead of SLE references.
+ *
+ *  @param view The apply view for making changes
+ *  @param account The account ID
+ *  @param sponsor The optional sponsor account ID
+ *  @param count Amount to add to the owner count
+ *  @param j Journal for logging
+ */
+inline void
+increaseOwnerCount(
+    ApplyView& view,
+    AccountID const& account,
+    std::optional<AccountID> const& sponsor,
+    std::uint32_t count,
+    beast::Journal j)
+{
+    increaseOwnerCount(
+        view,
+        view.peek(keylet::account(account)),
+        sponsor ? view.peek(keylet::account(*sponsor)) : SLE::pointer(),
+        count,
+        j);
+}
+
+/** Decrease owner-count fields when the caller supplies the sponsor.
+ *
+ *  This helper does not delete a ledger object. It updates reserve accounting
+ *  after the caller has removed an owner-counted reserve, or for special
+ *  owner-count changes whose sponsor cannot be derived from an object's
+ *  sfSponsor field.
+ *
+ *  @param view The apply view for making changes
+ *  @param accountSle The account's ledger entry
+ *  @param sponsorSle The sponsor's ledger entry (if applicable)
+ *  @param count Amount to remove from the owner count
+ *  @param j Journal for logging
+ */
+void
+decreaseOwnerCount(
+    ApplyView& view,
+    SLE::ref accountSle,
+    SLE::ref sponsorSle,
+    std::uint32_t count,
+    beast::Journal j);
+
+/** Convenience overload that accepts AccountID instead of SLE references.
+ *
+ *  @param view The apply view for making changes
+ *  @param account The account ID
+ *  @param sponsor The optional sponsor account ID
+ *  @param count Amount to remove from the owner count
+ *  @param j Journal for logging
+ */
+inline void
+decreaseOwnerCount(
+    ApplyView& view,
+    AccountID const& account,
+    std::optional<AccountID> const& sponsor,
+    std::uint32_t count,
+    beast::Journal j)
+{
+    decreaseOwnerCount(
+        view,
+        view.peek(keylet::account(account)),
+        sponsor ? view.peek(keylet::account(*sponsor)) : SLE::pointer(),
+        count,
+        j);
+}
+
+/** Decrease owner-count fields for an existing ledger object.
+ *
+ *  This helper derives the reserve sponsor from objectSle's sfSponsor field,
+ *  then updates the same owner-count fields as decreaseOwnerCount. Use this
+ *  when removing an existing object whose reserve sponsor is stored on that
+ *  object.
+ *
+ *  @param view The apply view for making changes
+ *  @param accountSle The account's ledger entry
+ *  @param objectSle The object's ledger entry
+ *  @param count Amount to remove from the owner count
+ *  @param j Journal for logging
+ */
+void
+decreaseOwnerCountForObject(
+    ApplyView& view,
+    SLE::ref accountSle,
+    SLE::ref objectSle,
+    std::uint32_t count,
+    beast::Journal j);
+
+/** Convenience overload that accepts AccountID instead of account SLE reference.
+ *
+ *  @param view The apply view for making changes
+ *  @param account The account ID
+ *  @param objectSle The object's ledger entry
+ *  @param count Amount to remove from the owner count
+ *  @param j Journal for logging
+ */
+inline void
+decreaseOwnerCountForObject(
+    ApplyView& view,
+    AccountID const& account,
+    SLE::ref objectSle,
+    std::uint32_t count,
+    beast::Journal j)
+{
+    SLE::ref accountSle = view.peek(keylet::account(account));
+    decreaseOwnerCountForObject(view, accountSle, objectSle, count, j);
+}
+
+/** Adjust a LoanBroker's owner count.
+ *
+ *  A LoanBroker's sfOwnerCount tracks the number of outstanding loans on
+ *  that broker; it is not a reserve-backed owner count and is distinct
+ *  from the broker's pseudo-account's owner count. Loans can never carry a
+ *  reserve sponsor (LoanSet rejects reserve sponsorship at preflight), so
+ *  this never involves sponsor accounting and never invokes the
+ *  ownerCountHook used for ACCOUNT_ROOT reserve tracking.
+ *
+ *  @param view The apply view for making changes
+ *  @param brokerSle The LoanBroker's ledger entry
+ *  @param delta Amount to add (positive) or remove (negative) from the count
+ *  @param j Journal for logging
+ */
+void
+adjustLoanBrokerOwnerCount(
+    ApplyView& view,
+    SLE::ref brokerSle,
+    std::int32_t delta,
+    beast::Journal j);
 
 /** Returns IOU issuer transfer fee as Rate. Rate specifies
  * the fee as fractions of 1 billion. For example, 1% transfer rate

include/xrpl/ledger/helpers/EscrowHelpers.h

@@ -6,6 +6,7 @@
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/MPTokenHelpers.h>
 #include <xrpl/ledger/helpers/RippleStateHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/ledger/helpers/TokenHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Concepts.h>
@@ -22,17 +23,15 @@
 #include <xrpl/protocol/TER.h>
 #include <xrpl/protocol/UintTypes.h>
 
-#include <cstdint>
-
 namespace xrpl {
 
 template <ValidIssueType T>
 TER
 escrowUnlockApplyHelper(
-    ApplyView& view,
+    ApplyViewContext ctx,
     Rate lockedRate,
     SLE::ref sleDest,
-    STAmount const& xrpBalance,
+    XRPAmount xrpBalance,
     STAmount const& amount,
     AccountID const& issuer,
     AccountID const& sender,
@@ -43,10 +42,10 @@ escrowUnlockApplyHelper(
 template <>
 inline TER
 escrowUnlockApplyHelper<Issue>(
-    ApplyView& view,
+    ApplyViewContext ctx,
     Rate lockedRate,
     SLE::ref sleDest,
-    STAmount const& xrpBalance,
+    XRPAmount xrpBalance,
     STAmount const& amount,
     AccountID const& issuer,
     AccountID const& sender,
@@ -66,16 +65,26 @@ escrowUnlockApplyHelper<Issue>(
     if (receiverIssuer)
         return tesSUCCESS;
 
-    if (!view.exists(trustLineKey) && createAsset)
+    if (!ctx.view.exists(trustLineKey) && createAsset)
     {
         // Can the account cover the trust line's reserve?
-        if (std::uint32_t const ownerCount = {sleDest->at(sfOwnerCount)};
-            xrpBalance < view.fees().accountReserve(ownerCount + 1))
+        auto const sponsorSle = getEffectiveTxReserveSponsor(ctx, sleDest);
+        if (!sponsorSle)
+            return sponsorSle.error();  // LCOV_EXCL_LINE
+
+        if (auto const ret = checkReserve(
+                ctx,
+                sleDest,
+                xrpBalance,
+                *sponsorSle,
+                {.ownerCountDelta = 1},
+                journal,
+                tecNO_LINE_INSUF_RESERVE);
+            !isTesSuccess(ret))
         {
             JLOG(journal.trace()) << "Trust line does not exist. "
                                      "Insufficient reserve to create line.";
-
-            return tecNO_LINE_INSUF_RESERVE;
+            return ret;
         }
 
         Currency const currency = issue.currency;
@@ -83,7 +92,7 @@ escrowUnlockApplyHelper<Issue>(
         initialBalance.get<Issue>().account = noAccount();
 
         if (TER const ter = trustCreate(
-                view,                                // payment sandbox
+                ctx.view,                            // payment sandbox
                 recvLow,                             // is dest low?
                 issuer,                              // source
                 receiver,                            // destination
@@ -97,19 +106,20 @@ escrowUnlockApplyHelper<Issue>(
                 Issue(currency, receiver),           // limit of zero
                 0,                                   // quality in
                 0,                                   // quality out
+                *sponsorSle,                         // sponsor
                 journal);                            // journal
             !isTesSuccess(ter))
         {
             return ter;  // LCOV_EXCL_LINE
         }
 
-        view.update(sleDest);
+        ctx.view.update(sleDest);
     }
 
-    if (!view.exists(trustLineKey) && !receiverIssuer)
+    if (!ctx.view.exists(trustLineKey) && !receiverIssuer)
         return tecNO_LINE;
 
-    auto const xferRate = transferRate(view, amount);
+    auto const xferRate = transferRate(ctx.view, amount);
     // update if issuer rate is less than locked rate
     if (xferRate < lockedRate)
         lockedRate = xferRate;
@@ -137,7 +147,7 @@ escrowUnlockApplyHelper<Issue>(
     // of the funds
     if (!createAsset)
     {
-        auto const sleRippleState = view.peek(trustLineKey);
+        auto const sleRippleState = ctx.view.peek(trustLineKey);
         if (!sleRippleState)
             return tecINTERNAL;  // LCOV_EXCL_LINE
 
@@ -163,7 +173,7 @@ escrowUnlockApplyHelper<Issue>(
     // if destination is not the issuer then transfer funds
     if (!receiverIssuer)
     {
-        auto const ter = directSendNoFee(view, issuer, receiver, finalAmt, true, journal);
+        auto const ter = directSendNoFee(ctx.view, issuer, receiver, finalAmt, true, journal);
         if (!isTesSuccess(ter))
             return ter;  // LCOV_EXCL_LINE
     }
@@ -173,10 +183,10 @@ escrowUnlockApplyHelper<Issue>(
 template <>
 inline TER
 escrowUnlockApplyHelper<MPTIssue>(
-    ApplyView& view,
+    ApplyViewContext ctx,
     Rate lockedRate,
     SLE::ref sleDest,
-    STAmount const& xrpBalance,
+    XRPAmount xrpBalance,
     STAmount const& amount,
     AccountID const& issuer,
     AccountID const& sender,
@@ -189,27 +199,32 @@ escrowUnlockApplyHelper<MPTIssue>(
 
     auto const mptID = amount.get<MPTIssue>().getMptID();
     auto const issuanceKey = keylet::mptokenIssuance(mptID);
-    if (!view.exists(keylet::mptoken(issuanceKey.key, receiver)) && createAsset && !receiverIssuer)
+    auto const mptKeylet = keylet::mptoken(issuanceKey.key, receiver);
+    if (!ctx.view.exists(mptKeylet) && createAsset && !receiverIssuer)
     {
-        if (std::uint32_t const ownerCount = {sleDest->at(sfOwnerCount)};
-            xrpBalance < view.fees().accountReserve(ownerCount + 1))
-        {
-            return tecINSUFFICIENT_RESERVE;
-        }
+        auto const sponsorSle = getEffectiveTxReserveSponsor(ctx, sleDest);
+        if (!sponsorSle)
+            return sponsorSle.error();  // LCOV_EXCL_LINE
 
-        if (auto const ter = createMPToken(view, mptID, receiver, 0); !isTesSuccess(ter))
+        if (auto const ret = checkReserve(
+                ctx, sleDest, xrpBalance, *sponsorSle, {.ownerCountDelta = 1}, journal);
+            !isTesSuccess(ret))
+            return ret;
+
+        if (auto const ter = createMPToken(ctx.view, mptID, receiver, *sponsorSle, 0);
+            !isTesSuccess(ter))
         {
             return ter;  // LCOV_EXCL_LINE
         }
 
         // update owner count.
-        adjustOwnerCount(view, sleDest, 1, journal);
+        increaseOwnerCount(ctx.view, sleDest, *sponsorSle, 1, journal);
     }
 
-    if (!view.exists(keylet::mptoken(issuanceKey.key, receiver)) && !receiverIssuer)
+    if (!ctx.view.exists(mptKeylet) && !receiverIssuer)
         return tecNO_PERMISSION;
 
-    auto const xferRate = transferRate(view, amount);
+    auto const xferRate = transferRate(ctx.view, amount);
     // update if issuer rate is less than locked rate
     if (xferRate < lockedRate)
         lockedRate = xferRate;
@@ -232,11 +247,11 @@ escrowUnlockApplyHelper<MPTIssue>(
         finalAmt = amount.value() - xferFee;
     }
     return unlockEscrowMPT(
-        view,
+        ctx.view,
         sender,
         receiver,
         finalAmt,
-        view.rules().enabled(fixTokenEscrowV1) ? amount : finalAmt,
+        ctx.view.rules().enabled(fixTokenEscrowV1) ? amount : finalAmt,
         journal);
 }
 

include/xrpl/ledger/helpers/MPTokenHelpers.h

@@ -86,7 +86,7 @@ canAddHolding(ReadView const& view, MPTIssue const& mptIssue);
 
 [[nodiscard]] TER
 authorizeMPToken(
-    ApplyView& view,
+    ApplyViewContext ctx,
     XRPAmount const& priorBalance,
     MPTID const& mptIssuanceID,
     AccountID const& account,
@@ -117,7 +117,7 @@ requireAuth(
  */
 [[nodiscard]] TER
 enforceMPTokenAuthorization(
-    ApplyView& view,
+    ApplyViewContext ctx,
     MPTID const& mptIssuanceID,
     AccountID const& account,
     XRPAmount const& priorBalance,
@@ -203,7 +203,7 @@ canMPTTradeAndTransfer(
 
 [[nodiscard]] TER
 addEmptyHolding(
-    ApplyView& view,
+    ApplyViewContext ctx,
     AccountID const& accountID,
     XRPAmount priorBalance,
     MPTIssue const& mptIssue,
@@ -211,7 +211,7 @@ addEmptyHolding(
 
 [[nodiscard]] TER
 removeEmptyHolding(
-    ApplyView& view,
+    ApplyViewContext ctx,
     AccountID const& accountID,
     MPTIssue const& mptIssue,
     beast::Journal journal);
@@ -243,6 +243,7 @@ createMPToken(
     ApplyView& view,
     MPTID const& mptIssuanceID,
     AccountID const& account,
+    SLE::ref sponsorSle,
     std::uint32_t const flags);
 
 TER
@@ -250,6 +251,7 @@ checkCreateMPT(
     xrpl::ApplyView& view,
     xrpl::MPTIssue const& mptIssue,
     xrpl::AccountID const& holder,
+    SLE::ref sponsorSle,
     beast::Journal j);
 
 //------------------------------------------------------------------------------

include/xrpl/ledger/helpers/OracleHelpers.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <xrpl/protocol/SField.h>
+#include <xrpl/protocol/STArray.h>  // IWYU pragma: keep
+#include <xrpl/protocol/STLedgerEntry.h>
+
+#include <cstddef>
+#include <cstdint>
+
+namespace xrpl {
+
+constexpr std::uint32_t kMinOracleReserveCount = 1;
+constexpr std::uint32_t kMaxOracleReserveCount = 2;
+constexpr std::size_t kOracleReserveCountThreshold = 5;
+
+template <typename T>
+    requires requires(T const& t) { t.size(); }
+inline std::uint32_t
+calculateOracleReserve(T const& priceDataSeries)
+{
+    return priceDataSeries.size() > kOracleReserveCountThreshold ? kMaxOracleReserveCount
+                                                                 : kMinOracleReserveCount;
+}
+
+inline std::uint32_t
+calculateOracleReserve(SLE::const_ref oracleSle)
+{
+    return calculateOracleReserve(oracleSle->getFieldArray(sfPriceDataSeries));
+}
+
+}  // namespace xrpl

include/xrpl/ledger/helpers/RippleStateHelpers.h

@@ -156,6 +156,7 @@ trustCreate(
                                 // Issuer should be the account being set.
     std::uint32_t uQualityIn,
     std::uint32_t uQualityOut,
+    SLE::ref sponsorSle,
     beast::Journal j);
 
 [[nodiscard]] TER
@@ -178,6 +179,7 @@ issueIOU(
     AccountID const& account,
     STAmount const& amount,
     Issue const& issue,
+    SLE::ref sponsorSle,
     beast::Journal j);
 
 [[nodiscard]] TER
@@ -235,7 +237,7 @@ canTransfer(ReadView const& view, Issue const& issue, AccountID const& from, Acc
 /// canAddHolding() in preflight with the same View and Asset
 [[nodiscard]] TER
 addEmptyHolding(
-    ApplyView& view,
+    ApplyViewContext ctx,
     AccountID const& accountID,
     XRPAmount priorBalance,
     Issue const& issue,
@@ -243,7 +245,7 @@ addEmptyHolding(
 
 [[nodiscard]] TER
 removeEmptyHolding(
-    ApplyView& view,
+    ApplyViewContext ctx,
     AccountID const& accountID,
     Issue const& issue,
     beast::Journal journal);

include/xrpl/ledger/helpers/SponsorHelpers.h

@@ -0,0 +1,184 @@
+#pragma once
+
+#include <xrpl/ledger/ApplyView.h>
+#include <xrpl/ledger/ReadView.h>
+#include <xrpl/protocol/AccountID.h>
+#include <xrpl/protocol/SField.h>
+#include <xrpl/protocol/STLedgerEntry.h>
+#include <xrpl/protocol/STTx.h>
+#include <xrpl/protocol/TER.h>
+#include <xrpl/protocol/TxFlags.h>
+#include <xrpl/protocol/TxFormats.h>
+
+#include <cstdint>
+#include <expected>
+#include <optional>
+
+namespace xrpl {
+
+/** Whether the given transaction type may use reserve sponsorship (v1).
+ *
+ *  Reserve sponsorship is restricted to an explicit allow-list of transaction
+ *  types; all others reject spfSponsorReserve at preflight.
+ */
+bool
+isReserveSponsorAllowed(TxType txType);
+
+/** Whether the transaction's fee is sponsored (sfSponsor present + spfSponsorFee set). */
+inline bool
+isFeeSponsored(STTx const& tx)
+{
+    return tx.isFieldPresent(sfSponsor) && ((tx.getFieldU32(sfSponsorFlags) & spfSponsorFee) != 0u);
+}
+
+/** Whether the transaction's reserve is sponsored (sfSponsor present + spfSponsorReserve set). */
+inline bool
+isReserveSponsored(STTx const& tx)
+{
+    return tx.isFieldPresent(sfSponsor) &&
+        ((tx.getFieldU32(sfSponsorFlags) & spfSponsorReserve) != 0u);
+}
+
+/** Return the AccountID of the transaction's reserve sponsor, or nullopt if unsponsored. */
+std::optional<AccountID>
+getTxReserveSponsorID(STTx const& tx);
+
+/** Return a mutable SLE for the transaction's reserve sponsor account.
+ *
+ *  @param ctx The apply-view context (view + tx)
+ *  @return The sponsor account SLE, a null pointer if the tx is not
+ *          reserve-sponsored, or tecINTERNAL if the sponsor account cannot
+ *          be loaded (an already-checked invariant).
+ */
+std::expected<SLE::pointer, TER>
+getTxReserveSponsor(ApplyViewContext ctx);
+
+/** Return a read-only SLE for the transaction's reserve sponsor account.
+ *
+ *  @param view The ledger read view
+ *  @param tx   The transaction to inspect
+ *  @return The sponsor account SLE, a null pointer if the tx is not
+ *          reserve-sponsored, or tecINTERNAL if the sponsor account cannot
+ *          be loaded (an already-checked invariant).
+ */
+std::expected<SLE::const_pointer, TER>
+getTxReserveSponsor(ReadView const& view, STTx const& tx);
+
+/** The transaction's reserve sponsor for the given account, if applicable.
+ *
+ *  A reserve sponsor only covers the transaction submitter's own objects, so
+ *  this returns the tx reserve sponsor SLE only when accountSle is the tx's own
+ *  (non-pseudo) account; otherwise it returns a null sponsor pointer. This is
+ *  the single source of truth for the "sponsor applies to tx.Account only" rule
+ *  that the sponsor-deriving helper overloads in AccountRootHelpers rely on.
+ *
+ *  @param ctx The apply-view context (view + tx)
+ *  @param accountSle The account whose sponsor is being resolved
+ *  @return The sponsor SLE (nullptr if unsponsored), or tecINTERNAL if the
+ *          sponsor account cannot be loaded (an already-checked invariant)
+ */
+[[nodiscard]] std::expected<SLE::pointer, TER>
+getEffectiveTxReserveSponsor(ApplyViewContext ctx, SLE::const_ref accountSle);
+
+/** Return the AccountID stored in the given sponsor field of a ledger entry, or nullopt if absent.
+ */
+std::optional<AccountID>
+getLedgerEntryReserveSponsorID(SLE::const_ref sle, SF_ACCOUNT const& field = sfSponsor);
+
+/** Return a mutable SLE for the reserve sponsor recorded on a ledger entry.
+ *
+ *  Reads the sponsor AccountID from @p field on @p sle and peeks the
+ *  corresponding account root in @p view.
+ *
+ *  @param view  The mutable apply view
+ *  @param sle   The ledger entry whose sponsor field is inspected
+ *  @param field The field that holds the sponsor AccountID (defaults to sfSponsor)
+ *  @return The sponsor account SLE, or a null pointer if the entry is unsponsored.
+ */
+SLE::pointer
+getLedgerEntryReserveSponsor(
+    ApplyView& view,
+    SLE::const_ref sle,
+    SF_ACCOUNT const& field = sfSponsor);
+
+/** Stamp a reserve sponsor onto a ledger entry using an explicit sponsor SLE.
+ *
+ *  Sets @p field on @p sle to the AccountID from @p sponsorSle. A no-op when
+ *  @p sponsorSle is null (unsponsored). For RippleState entries the field must
+ *  be sfHighSponsor or sfLowSponsor; for all other entry types it must be
+ *  sfSponsor.
+ *
+ *  @param sle       The ledger entry to stamp
+ *  @param sponsorSle The sponsor's account root SLE (null → no-op)
+ *  @param field     The sponsor field to set (defaults to sfSponsor)
+ */
+void
+addSponsorToLedgerEntry(
+    SLE::ref sle,
+    SLE::const_ref sponsorSle,
+    SF_ACCOUNT const& field = sfSponsor);
+
+/** Stamp the transaction's reserve sponsor onto a newly-created ledger entry.
+ *
+ *  Equivalent to the overload above, but resolves the sponsor via
+ *  getTxReserveSponsor(ctx) instead of taking it explicitly. A no-op when the
+ *  transaction is not reserve-sponsored. The entry is assumed to be owned by
+ *  the transaction submitter, which is the only account a tx reserve sponsor
+ *  can cover.
+ */
+void
+addSponsorToLedgerEntry(ApplyViewContext ctx, SLE::ref sle, SF_ACCOUNT const& field = sfSponsor);
+
+/** Remove the reserve sponsor field from a ledger entry.
+ *
+ *  A no-op when @p field is not present on @p sle. For RippleState entries
+ *  the field must be sfHighSponsor or sfLowSponsor; for all other entry types
+ *  it must be sfSponsor.
+ *
+ *  @param sle   The ledger entry to modify
+ *  @param field The sponsor field to clear (defaults to sfSponsor)
+ */
+void
+removeSponsorFromLedgerEntry(SLE::ref sle, SF_ACCOUNT const& field = sfSponsor);
+
+/** Whether @p account is the owner of a ledger entry for sponsorship purposes.
+ *
+ *  Ownership rules vary by entry type. For RippleState entries the owner is
+ *  whichever side of the trust line holds the reserve. For credentials, the
+ *  owner is the subject once accepted and the issuer before acceptance.
+ *
+ *  @param view    The ledger read view (used for SignerList lookup)
+ *  @param sle     The ledger entry whose owner is checked
+ *  @param account The candidate account to match against
+ *  @return true if @p account owns @p sle, false otherwise.
+ */
+bool
+isLedgerEntryOwner(ReadView const& view, SLE const& sle, AccountID const& account);
+
+/** Whether this ledger entry type can have a reserve sponsor attached to it. */
+bool
+isLedgerEntrySupportedBySponsorship(SLE const& sle);
+
+/** Return the number of owner-count units the ledger entry consumes.
+ *
+ *  Most entries cost 1. Exceptions: Oracles scale with their price-data series
+ *  size, Vaults cost 2 (vault + pseudo-account), and legacy SignerList entries
+ *  (pre-MultiSignReserve) cost 2 + signer count.
+ */
+std::uint32_t
+getLedgerEntryOwnerCount(SLE const& sle);
+
+/** Return the SField used to store the reserve sponsor for @p owner on @p sle.
+ *
+ *  For most entry types this is sfSponsor. RippleState entries use
+ *  sfHighSponsor or sfLowSponsor depending on which side of the trust line
+ *  @p owner holds.
+ *
+ *  @param sle   The ledger entry
+ *  @param owner The account whose sponsor field is needed
+ *  @return sfHighSponsor, sfLowSponsor, or sfSponsor as appropriate.
+ */
+SF_ACCOUNT const&
+getLedgerEntrySponsorField(SLE const& sle, AccountID const& owner);
+
+}  // namespace xrpl

include/xrpl/ledger/helpers/TokenHelpers.h

@@ -10,6 +10,7 @@
 #include <xrpl/protocol/MPTIssue.h>
 #include <xrpl/protocol/Rate.h>
 #include <xrpl/protocol/STAmount.h>
+#include <xrpl/protocol/STLedgerEntry.h>
 #include <xrpl/protocol/TER.h>
 #include <xrpl/protocol/UintTypes.h>
 #include <xrpl/protocol/XRPAmount.h>
@@ -302,7 +303,7 @@ canAddHolding(ReadView const& view, Asset const& asset);
 
 [[nodiscard]] TER
 addEmptyHolding(
-    ApplyView& view,
+    ApplyViewContext ctx,
     AccountID const& accountID,
     XRPAmount priorBalance,
     Asset const& asset,
@@ -310,7 +311,7 @@ addEmptyHolding(
 
 [[nodiscard]] TER
 removeEmptyHolding(
-    ApplyView& view,
+    ApplyViewContext ctx,
     AccountID const& accountID,
     Asset const& asset,
     beast::Journal journal);
@@ -371,6 +372,7 @@ accountSend(
     AccountID const& to,
     STAmount const& saAmount,
     beast::Journal j,
+    SLE::ref sponsorSle = {},
     WaiveTransferFee waiveFee = WaiveTransferFee::No,
     AllowMPTOverflow allowOverflow = AllowMPTOverflow::No);
 

include/xrpl/protocol/Book.h

@@ -74,9 +74,9 @@ operator==(Book const& lhs, Book const& rhs)
 [[nodiscard]] constexpr std::weak_ordering
 operator<=>(Book const& lhs, Book const& rhs)
 {
-    if (auto const c{lhs.in <=> rhs.in}; c != 0)
+    if (auto const c{lhs.in <=> rhs.in}; c != 0)  // NOLINT(modernize-use-nullptr)
         return c;
-    if (auto const c{lhs.out <=> rhs.out}; c != 0)
+    if (auto const c{lhs.out <=> rhs.out}; c != 0)  // NOLINT(modernize-use-nullptr)
         return c;
 
     // Manually compare optionals

include/xrpl/protocol/Fees.h

@@ -2,7 +2,6 @@
 
 #include <xrpl/protocol/XRPAmount.h>
 
-#include <cstddef>
 #include <cstdint>
 
 namespace xrpl {
@@ -39,13 +38,13 @@ struct Fees
 
     /** Returns the account reserve given the owner count, in drops.
 
-        The reserve is calculated as the reserve base plus
-        the reserve increment times the number of increments.
+        The reserve is calculated as the reserve base times the number of accounts plus the reserve
+        increment times the number of increments.
     */
     [[nodiscard]] XRPAmount
-    accountReserve(std::size_t ownerCount) const
+    accountReserve(std::uint32_t ownerCount, std::uint32_t accountCount) const
     {
-        return reserve + ownerCount * increment;
+        return (reserve * accountCount) + (increment * ownerCount);
     }
 };
 

include/xrpl/protocol/Indexes.h

@@ -142,6 +142,10 @@ ticket(uint256 const& key)
 Keylet
 signerList(AccountID const& account) noexcept;
 
+/** A Sponsorship */
+Keylet
+sponsorship(AccountID const& sponsor, AccountID const& sponsee) noexcept;
+
 /** A Check */
 /** @{ */
 Keylet

include/xrpl/protocol/Issue.h

@@ -84,7 +84,7 @@ operator==(Issue const& lhs, Issue const& rhs)
 [[nodiscard]] constexpr std::weak_ordering
 operator<=>(Issue const& lhs, Issue const& rhs)
 {
-    if (auto const c{lhs.currency <=> rhs.currency}; c != 0)
+    if (auto const c{lhs.currency <=> rhs.currency}; c != 0)  // NOLINT(modernize-use-nullptr)
         return c;
 
     if (isXRP(lhs.currency))

include/xrpl/protocol/LedgerFormats.h

@@ -208,7 +208,11 @@ enum LedgerEntryType : std::uint16_t {
     LEDGER_OBJECT(Loan,                                                                                                            \
         LSF_FLAG(lsfLoanDefault, 0x00010000)                                                                                       \
         LSF_FLAG(lsfLoanImpaired, 0x00020000)                                                                                      \
-        LSF_FLAG(lsfLoanOverpayment, 0x00040000))               /* True, loan allows overpayments */
+        LSF_FLAG(lsfLoanOverpayment, 0x00040000))               /* True, loan allows overpayments */                               \
+                                                                                                                                   \
+    LEDGER_OBJECT(Sponsorship,                                                                                                     \
+        LSF_FLAG(lsfSponsorshipRequireSignForFee, 0x00010000)                                                                      \
+        LSF_FLAG(lsfSponsorshipRequireSignForReserve, 0x00020000))
 
 // clang-format on
 

include/xrpl/protocol/STObject.h

@@ -229,10 +229,10 @@ public:
     [[nodiscard]] AccountID
     getAccountID(SField const& field) const;
 
-    /** The account responsible for the fee and authorization: the delegate when
+    /** The account responsible for the authorization: the delegate when
         sfDelegate is present, otherwise the account. */
     [[nodiscard]] AccountID
-    getFeePayer() const;
+    getInitiator() const;
 
     [[nodiscard]] Blob
     getFieldVL(SField const& field) const;

include/xrpl/protocol/STTx.h

@@ -141,6 +141,9 @@ public:
     [[nodiscard]] std::vector<uint256> const&
     getBatchTransactionIDs() const;
 
+    [[nodiscard]] AccountID
+    getFeePayerID() const;
+
 private:
     /** Check the signature.
         @param rules The current ledger rules.

include/xrpl/protocol/TER.h

@@ -225,6 +225,7 @@ enum TERcodes : TERUnderlyingType {
                                 // create a pseudo-account
     terNO_DELEGATE_PERMISSION,  // Delegate does not have permission
     terLOCKED,                  // MPT is locked
+    terNO_PERMISSION,           // No permission but retry
 };
 
 //------------------------------------------------------------------------------
@@ -368,6 +369,7 @@ enum TECcodes : TERUnderlyingType {
     // reclaimed after those networks reset.
     tecNO_DELEGATE_PERMISSION = 198,
     tecBAD_PROOF = 199,
+    tecNO_SPONSOR_PERMISSION = 200,
 };
 
 //------------------------------------------------------------------------------

include/xrpl/protocol/TxFlags.h

@@ -102,7 +102,8 @@ inline constexpr FlagValue tfUniversalMask = ~tfUniversal;
     TRANSACTION(Payment,                                                                                                                                       \
         TF_FLAG(tfNoRippleDirect, 0x00010000)                                                                                                                  \
         TF_FLAG(tfPartialPayment, 0x00020000)                                                                                                                  \
-        TF_FLAG(tfLimitQuality, 0x00040000),                                                                                                                   \
+        TF_FLAG(tfLimitQuality, 0x00040000)                                                                                                                    \
+        TF_FLAG(tfSponsorCreatedAccount, 0x00080000),                                                                                                          \
         MASK_ADJ(0))                                                                                                                                           \
                                                                                                                                                                \
     TRANSACTION(TrustSet,                                                                                                                                      \
@@ -141,7 +142,7 @@ inline constexpr FlagValue tfUniversalMask = ~tfUniversal;
         TF_FLAG(tfMPTCanTrade, lsfMPTCanTrade)                                                                                                                 \
         TF_FLAG(tfMPTCanTransfer, lsfMPTCanTransfer)                                                                                                           \
         TF_FLAG(tfMPTCanClawback, lsfMPTCanClawback)                                                                                                           \
-        TF_FLAG(tfMPTCanHoldConfidentialBalance, lsfMPTCanHoldConfidentialBalance),                                                                                                            \
+        TF_FLAG(tfMPTCanHoldConfidentialBalance, lsfMPTCanHoldConfidentialBalance),                                                                            \
         MASK_ADJ(0))                                                                                                                                           \
                                                                                                                                                                \
     TRANSACTION(MPTokenAuthorize,                                                                                                                              \
@@ -215,6 +216,20 @@ inline constexpr FlagValue tfUniversalMask = ~tfUniversal;
         TF_FLAG(tfLoanDefault, 0x00010000)                                                                                                                     \
         TF_FLAG(tfLoanImpair, 0x00020000)                                                                                                                      \
         TF_FLAG(tfLoanUnimpair, 0x00040000),                                                                                                                   \
+        MASK_ADJ(0))                                                                                                                                           \
+                                                                                                                                                               \
+    TRANSACTION(SponsorshipSet,                                                                                                                                \
+        TF_FLAG(tfSponsorshipSetRequireSignForFee, 0x00010000)                                                                                                 \
+        TF_FLAG(tfSponsorshipClearRequireSignForFee, 0x00020000)                                                                                               \
+        TF_FLAG(tfSponsorshipSetRequireSignForReserve, 0x00040000)                                                                                             \
+        TF_FLAG(tfSponsorshipClearRequireSignForReserve, 0x00080000)                                                                                           \
+        TF_FLAG(tfDeleteObject, 0x00100000),                                                                                                                   \
+        MASK_ADJ(0))                                                                                                                                           \
+                                                                                                                                                               \
+    TRANSACTION(SponsorshipTransfer,                                                                                                                           \
+        TF_FLAG(tfSponsorshipEnd, 0x00010000)                                                                                                                  \
+        TF_FLAG(tfSponsorshipCreate, 0x00020000)                                                                                                               \
+        TF_FLAG(tfSponsorshipReassign, 0x00040000),                                                                                                            \
         MASK_ADJ(0))
 
 // clang-format on
@@ -444,6 +459,12 @@ getAsfFlagMap()
 #pragma pop_macro("ACCOUNTSET_FLAG_TO_MAP")
 #pragma pop_macro("ACCOUNTSET_FLAGS")
 
+// Sponsor flags (spf)
+
+inline constexpr FlagValue spfSponsorFee = 1;
+inline constexpr FlagValue spfSponsorReserve = 2;
+inline constexpr FlagValue spfSponsorFlagMask = ~(spfSponsorFee | spfSponsorReserve);
+
 }  // namespace xrpl
 
 // NOLINTEND(readability-identifier-naming)

include/xrpl/protocol/detail/features.macro

@@ -15,6 +15,7 @@
 // Add new amendments to the top of this list.
 // Keep it sorted in reverse chronological order.
 
+XRPL_FEATURE(Sponsor,                     Supported::Yes, VoteBehavior::DefaultNo)
 XRPL_FEATURE(BatchV1_1,                   Supported::Yes, VoteBehavior::DefaultNo)
 XRPL_FEATURE(LendingProtocolV1_1,         Supported::No,  VoteBehavior::DefaultNo)
 XRPL_FEATURE(ConfidentialTransfer,        Supported::Yes, VoteBehavior::DefaultNo)

include/xrpl/protocol/detail/ledger_entries.macro

@@ -127,29 +127,32 @@ LEDGER_ENTRY(ltTICKET, 0x0054, Ticket, ticket, ({
     \sa keylet::account
  */
 LEDGER_ENTRY(ltACCOUNT_ROOT, 0x0061, AccountRoot, account, ({
-    {sfAccount,              SoeRequired},
-    {sfSequence,             SoeRequired},
-    {sfBalance,              SoeRequired},
-    {sfOwnerCount,           SoeRequired},
-    {sfPreviousTxnID,        SoeRequired},
-    {sfPreviousTxnLgrSeq,    SoeRequired},
-    {sfAccountTxnID,         SoeOptional},
-    {sfRegularKey,           SoeOptional},
-    {sfEmailHash,            SoeOptional},
-    {sfWalletLocator,        SoeOptional},
-    {sfWalletSize,           SoeOptional},
-    {sfMessageKey,           SoeOptional},
-    {sfTransferRate,         SoeOptional},
-    {sfDomain,               SoeOptional},
-    {sfTickSize,             SoeOptional},
-    {sfTicketCount,          SoeOptional},
-    {sfNFTokenMinter,        SoeOptional},
-    {sfMintedNFTokens,       SoeDefault},
-    {sfBurnedNFTokens,       SoeDefault},
-    {sfFirstNFTokenSequence, SoeOptional},
-    {sfAMMID,                SoeOptional}, // pseudo-account designator
-    {sfVaultID,              SoeOptional}, // pseudo-account designator
-    {sfLoanBrokerID,         SoeOptional}, // pseudo-account designator
+    {sfAccount,                SoeRequired},
+    {sfSequence,               SoeRequired},
+    {sfBalance,                SoeRequired},
+    {sfOwnerCount,             SoeRequired},
+    {sfPreviousTxnID,          SoeRequired},
+    {sfPreviousTxnLgrSeq,      SoeRequired},
+    {sfAccountTxnID,           SoeOptional},
+    {sfRegularKey,             SoeOptional},
+    {sfEmailHash,              SoeOptional},
+    {sfWalletLocator,          SoeOptional},
+    {sfWalletSize,             SoeOptional},
+    {sfMessageKey,             SoeOptional},
+    {sfTransferRate,           SoeOptional},
+    {sfDomain,                 SoeOptional},
+    {sfTickSize,               SoeOptional},
+    {sfTicketCount,            SoeOptional},
+    {sfNFTokenMinter,          SoeOptional},
+    {sfMintedNFTokens,         SoeDefault},
+    {sfBurnedNFTokens,         SoeDefault},
+    {sfFirstNFTokenSequence,   SoeOptional},
+    {sfSponsoredOwnerCount,    SoeDefault},
+    {sfSponsoringOwnerCount,   SoeDefault},
+    {sfSponsoringAccountCount, SoeDefault},
+    {sfAMMID,                  SoeOptional}, // pseudo-account designator
+    {sfVaultID,                SoeOptional}, // pseudo-account designator
+    {sfLoanBrokerID,           SoeOptional}, // pseudo-account designator
 }))
 
 /** A ledger object which contains a list of object identifiers.
@@ -286,6 +289,8 @@ LEDGER_ENTRY(ltRIPPLE_STATE, 0x0072, RippleState, state, ({
     {sfHighNode,             SoeOptional},
     {sfHighQualityIn,        SoeOptional},
     {sfHighQualityOut,       SoeOptional},
+    {sfHighSponsor,          SoeOptional},
+    {sfLowSponsor,           SoeOptional},
 }))
 
 /** The ledger object which lists the network's fee settings.
@@ -616,5 +621,20 @@ LEDGER_ENTRY(ltLOAN, 0x0089, Loan, loan, ({
     {sfLoanScale,                SoeDefault},
 }))
 
+/** A ledger object representing a sponsorship.
+    \sa keylet::sponsorship
+ */
+LEDGER_ENTRY(ltSPONSORSHIP, 0x0090, Sponsorship, sponsorship, ({
+    {sfPreviousTxnID,        SoeRequired},
+    {sfPreviousTxnLgrSeq,    SoeRequired},
+    {sfOwner,                SoeRequired},
+    {sfSponsee,              SoeRequired},
+    {sfFeeAmount,            SoeOptional},
+    {sfMaxFee,               SoeOptional},
+    {sfRemainingOwnerCount,  SoeDefault},
+    {sfOwnerNode,            SoeRequired},
+    {sfSponseeNode,          SoeRequired},
+}))
+
 #undef EXPAND
 #undef LEDGER_ENTRY_DUPLICATE

include/xrpl/protocol/detail/sfields.macro

@@ -114,6 +114,11 @@ TYPED_SFIELD(sfLateInterestRate,         UINT32,    66) // 1/10 basis points (bi
 TYPED_SFIELD(sfCloseInterestRate,        UINT32,    67) // 1/10 basis points (bips)
 TYPED_SFIELD(sfOverpaymentInterestRate,  UINT32,    68) // 1/10 basis points (bips)
 TYPED_SFIELD(sfConfidentialBalanceVersion, UINT32,  69)
+TYPED_SFIELD(sfSponsoredOwnerCount,      UINT32,    70)
+TYPED_SFIELD(sfSponsoringOwnerCount,     UINT32,    71)
+TYPED_SFIELD(sfSponsoringAccountCount,   UINT32,    72)
+TYPED_SFIELD(sfRemainingOwnerCount,      UINT32,    73)
+TYPED_SFIELD(sfSponsorFlags,             UINT32,    74)
 
 // 64-bit integers (common)
 TYPED_SFIELD(sfIndexNext,                UINT64,     1)
@@ -148,6 +153,7 @@ TYPED_SFIELD(sfLockedAmount,             UINT64,    29, SField::kSmdBaseTen|SFie
 TYPED_SFIELD(sfVaultNode,                UINT64,    30)
 TYPED_SFIELD(sfLoanBrokerNode,           UINT64,    31)
 TYPED_SFIELD(sfConfidentialOutstandingAmount, UINT64, 32, SField::kSmdBaseTen|SField::kSmdDefault)
+TYPED_SFIELD(sfSponseeNode,              UINT64,    33)
 
 // 128-bit
 TYPED_SFIELD(sfEmailHash,                UINT128,    1)
@@ -209,6 +215,7 @@ TYPED_SFIELD(sfLoanBrokerID,             UINT256,   37,
 TYPED_SFIELD(sfLoanID,                   UINT256,   38)
 TYPED_SFIELD(sfReferenceHolding,         UINT256,   39)
 TYPED_SFIELD(sfBlindingFactor,           UINT256,   40)
+TYPED_SFIELD(sfObjectID,                 UINT256,   41)
 
 // number (common)
 TYPED_SFIELD(sfNumber,                   NUMBER,     1)
@@ -268,6 +275,8 @@ TYPED_SFIELD(sfPrice,                    AMOUNT,    28)
 TYPED_SFIELD(sfSignatureReward,          AMOUNT,    29)
 TYPED_SFIELD(sfMinAccountCreateAmount,   AMOUNT,    30)
 TYPED_SFIELD(sfLPTokenBalance,           AMOUNT,    31)
+TYPED_SFIELD(sfFeeAmount,                AMOUNT,    32)
+TYPED_SFIELD(sfMaxFee,                   AMOUNT,    33)
 
 // variable length (common)
 TYPED_SFIELD(sfPublicKey,                VL,         1)
@@ -343,6 +352,11 @@ TYPED_SFIELD(sfIssuingChainDoor,         ACCOUNT,   23)
 TYPED_SFIELD(sfSubject,                  ACCOUNT,   24)
 TYPED_SFIELD(sfBorrower,                 ACCOUNT,   25)
 TYPED_SFIELD(sfCounterparty,             ACCOUNT,   26)
+TYPED_SFIELD(sfSponsor,                  ACCOUNT,   27)
+TYPED_SFIELD(sfHighSponsor,              ACCOUNT,   28)
+TYPED_SFIELD(sfLowSponsor,               ACCOUNT,   29)
+TYPED_SFIELD(sfCounterpartySponsor,      ACCOUNT,   30)
+TYPED_SFIELD(sfSponsee,                  ACCOUNT,   31)
 
 // vector of 256-bit
 TYPED_SFIELD(sfIndexes,                  VECTOR256,  1, SField::kSmdNever)
@@ -407,6 +421,7 @@ UNTYPED_SFIELD(sfRawTransaction,         OBJECT,    34)
 UNTYPED_SFIELD(sfBatchSigner,            OBJECT,    35)
 UNTYPED_SFIELD(sfBook,                   OBJECT,    36)
 UNTYPED_SFIELD(sfCounterpartySignature,  OBJECT,    37, SField::kSmdDefault, SField::kNotSigning)
+UNTYPED_SFIELD(sfSponsorSignature,       OBJECT,    38, SField::kSmdDefault, SField::kNotSigning)
 
 // array of objects (common)
 // ARRAY/1 is reserved for end of array

include/xrpl/protocol/detail/transactions.macro

@@ -1165,6 +1165,35 @@ TRANSACTION(ttCONFIDENTIAL_MPT_CLAWBACK, 89, ConfidentialMPTClawback,
     {sfZKProof, SoeRequired},
 }))
 
+/** This transaction transfers sponsorship on an object/account. */
+#if TRANSACTION_INCLUDE
+#   include <xrpl/tx/transactors/sponsor/SponsorshipTransfer.h>
+#endif
+TRANSACTION(ttSPONSORSHIP_TRANSFER, 90, SponsorshipTransfer,
+    Delegation::NotDelegable,
+    featureSponsor,
+    NoPriv,
+    ({
+    {sfObjectID, SoeOptional},
+    {sfSponsee, SoeOptional},
+}))
+
+/** This transaction creates a Sponsorship object. */
+#if TRANSACTION_INCLUDE
+#   include <xrpl/tx/transactors/sponsor/SponsorshipSet.h>
+#endif
+TRANSACTION(ttSPONSORSHIP_SET, 91, SponsorshipSet,
+    Delegation::Delegable,
+    featureSponsor,
+    NoPriv,
+    ({
+    {sfCounterpartySponsor, SoeOptional},
+    {sfSponsee, SoeOptional},
+    {sfFeeAmount, SoeOptional},
+    {sfMaxFee, SoeOptional},
+    {sfRemainingOwnerCount, SoeOptional},
+}))
+
 /** This system-generated transaction type is used to update the status of the various amendments.
 
     For details, see: https://xrpl.org/amendments.html

include/xrpl/protocol/jss.h

@@ -558,6 +558,9 @@ JSS(source_account);              // in: PathRequest, RipplePathFind
 JSS(source_amount);               // in: PathRequest, RipplePathFind
 JSS(source_currencies);           // in: PathRequest, RipplePathFind
 JSS(source_tag);                  // out: AccountChannels
+JSS(sponsee);                     // in: LedgerEntry
+JSS(sponsor);                     // in: LedgerEntry
+JSS(sponsored);                   // in: AccountObjects
 JSS(stand_alone);                 // out: NetworkOPs
 JSS(standard_deviation);          // out: get_aggregate_price
 JSS(start);                       // in: TxHistory

include/xrpl/protocol_autogen/ledger_entries/AccountRoot.h

@@ -447,6 +447,78 @@ public:
         return this->sle_->isFieldPresent(sfFirstNFTokenSequence);
     }
 
+    /**
+     * @brief Get sfSponsoredOwnerCount (SoeDefault)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_UINT32::type::value_type>
+    getSponsoredOwnerCount() const
+    {
+        if (hasSponsoredOwnerCount())
+            return this->sle_->at(sfSponsoredOwnerCount);
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfSponsoredOwnerCount is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasSponsoredOwnerCount() const
+    {
+        return this->sle_->isFieldPresent(sfSponsoredOwnerCount);
+    }
+
+    /**
+     * @brief Get sfSponsoringOwnerCount (SoeDefault)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_UINT32::type::value_type>
+    getSponsoringOwnerCount() const
+    {
+        if (hasSponsoringOwnerCount())
+            return this->sle_->at(sfSponsoringOwnerCount);
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfSponsoringOwnerCount is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasSponsoringOwnerCount() const
+    {
+        return this->sle_->isFieldPresent(sfSponsoringOwnerCount);
+    }
+
+    /**
+     * @brief Get sfSponsoringAccountCount (SoeDefault)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_UINT32::type::value_type>
+    getSponsoringAccountCount() const
+    {
+        if (hasSponsoringAccountCount())
+            return this->sle_->at(sfSponsoringAccountCount);
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfSponsoringAccountCount is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasSponsoringAccountCount() const
+    {
+        return this->sle_->isFieldPresent(sfSponsoringAccountCount);
+    }
+
     /**
      * @brief Get sfAMMID (SoeOptional)
      * @return The field value, or std::nullopt if not present.
@@ -786,6 +858,39 @@ public:
         return *this;
     }
 
+    /**
+     * @brief Set sfSponsoredOwnerCount (SoeDefault)
+     * @return Reference to this builder for method chaining.
+     */
+    AccountRootBuilder&
+    setSponsoredOwnerCount(std::decay_t<typename SF_UINT32::type::value_type> const& value)
+    {
+        object_[sfSponsoredOwnerCount] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfSponsoringOwnerCount (SoeDefault)
+     * @return Reference to this builder for method chaining.
+     */
+    AccountRootBuilder&
+    setSponsoringOwnerCount(std::decay_t<typename SF_UINT32::type::value_type> const& value)
+    {
+        object_[sfSponsoringOwnerCount] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfSponsoringAccountCount (SoeDefault)
+     * @return Reference to this builder for method chaining.
+     */
+    AccountRootBuilder&
+    setSponsoringAccountCount(std::decay_t<typename SF_UINT32::type::value_type> const& value)
+    {
+        object_[sfSponsoringAccountCount] = value;
+        return *this;
+    }
+
     /**
      * @brief Set sfAMMID (SoeOptional)
      * @return Reference to this builder for method chaining.

include/xrpl/protocol_autogen/ledger_entries/RippleState.h

@@ -243,6 +243,54 @@ public:
     {
         return this->sle_->isFieldPresent(sfHighQualityOut);
     }
+
+    /**
+     * @brief Get sfHighSponsor (SoeOptional)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_ACCOUNT::type::value_type>
+    getHighSponsor() const
+    {
+        if (hasHighSponsor())
+            return this->sle_->at(sfHighSponsor);
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfHighSponsor is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasHighSponsor() const
+    {
+        return this->sle_->isFieldPresent(sfHighSponsor);
+    }
+
+    /**
+     * @brief Get sfLowSponsor (SoeOptional)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_ACCOUNT::type::value_type>
+    getLowSponsor() const
+    {
+        if (hasLowSponsor())
+            return this->sle_->at(sfLowSponsor);
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfLowSponsor is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasLowSponsor() const
+    {
+        return this->sle_->isFieldPresent(sfLowSponsor);
+    }
 };
 
 /**
@@ -410,6 +458,28 @@ public:
         return *this;
     }
 
+    /**
+     * @brief Set sfHighSponsor (SoeOptional)
+     * @return Reference to this builder for method chaining.
+     */
+    RippleStateBuilder&
+    setHighSponsor(std::decay_t<typename SF_ACCOUNT::type::value_type> const& value)
+    {
+        object_[sfHighSponsor] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfLowSponsor (SoeOptional)
+     * @return Reference to this builder for method chaining.
+     */
+    RippleStateBuilder&
+    setLowSponsor(std::decay_t<typename SF_ACCOUNT::type::value_type> const& value)
+    {
+        object_[sfLowSponsor] = value;
+        return *this;
+    }
+
     /**
      * @brief Build and return the completed RippleState wrapper.
      * @param index The ledger entry index.

include/xrpl/protocol_autogen/ledger_entries/Sponsorship.h

@@ -0,0 +1,344 @@
+// This file is auto-generated. Do not edit.
+#pragma once
+
+#include <xrpl/protocol/STLedgerEntry.h>
+#include <xrpl/protocol/STParsedJSON.h>
+#include <xrpl/protocol/jss.h>
+#include <xrpl/protocol_autogen/LedgerEntryBase.h>
+#include <xrpl/protocol_autogen/LedgerEntryBuilderBase.h>
+#include <xrpl/json/json_value.h>
+
+#include <stdexcept>
+#include <optional>
+
+namespace xrpl::ledger_entries {
+
+class SponsorshipBuilder;
+
+/**
+ * @brief Ledger Entry: Sponsorship
+ *
+ * Type: ltSPONSORSHIP (0x0090)
+ * RPC Name: sponsorship
+ *
+ * Immutable wrapper around SLE providing type-safe field access.
+ * Use SponsorshipBuilder to construct new ledger entries.
+ */
+class Sponsorship : public LedgerEntryBase
+{
+public:
+    static constexpr LedgerEntryType entryType = ltSPONSORSHIP;
+
+    /**
+     * @brief Construct a Sponsorship ledger entry wrapper from an existing SLE object.
+     * @throws std::runtime_error if the ledger entry type doesn't match.
+     */
+    explicit Sponsorship(SLE::const_pointer sle)
+        : LedgerEntryBase(std::move(sle))
+    {
+        // Verify ledger entry type
+        if (sle_->getType() != entryType)
+        {
+            throw std::runtime_error("Invalid ledger entry type for Sponsorship");
+        }
+    }
+
+    // Ledger entry-specific field getters
+
+    /**
+     * @brief Get sfPreviousTxnID (SoeRequired)
+     * @return The field value.
+     */
+    [[nodiscard]]
+    SF_UINT256::type::value_type
+    getPreviousTxnID() const
+    {
+        return this->sle_->at(sfPreviousTxnID);
+    }
+
+    /**
+     * @brief Get sfPreviousTxnLgrSeq (SoeRequired)
+     * @return The field value.
+     */
+    [[nodiscard]]
+    SF_UINT32::type::value_type
+    getPreviousTxnLgrSeq() const
+    {
+        return this->sle_->at(sfPreviousTxnLgrSeq);
+    }
+
+    /**
+     * @brief Get sfOwner (SoeRequired)
+     * @return The field value.
+     */
+    [[nodiscard]]
+    SF_ACCOUNT::type::value_type
+    getOwner() const
+    {
+        return this->sle_->at(sfOwner);
+    }
+
+    /**
+     * @brief Get sfSponsee (SoeRequired)
+     * @return The field value.
+     */
+    [[nodiscard]]
+    SF_ACCOUNT::type::value_type
+    getSponsee() const
+    {
+        return this->sle_->at(sfSponsee);
+    }
+
+    /**
+     * @brief Get sfFeeAmount (SoeOptional)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_AMOUNT::type::value_type>
+    getFeeAmount() const
+    {
+        if (hasFeeAmount())
+            return this->sle_->at(sfFeeAmount);
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfFeeAmount is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasFeeAmount() const
+    {
+        return this->sle_->isFieldPresent(sfFeeAmount);
+    }
+
+    /**
+     * @brief Get sfMaxFee (SoeOptional)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_AMOUNT::type::value_type>
+    getMaxFee() const
+    {
+        if (hasMaxFee())
+            return this->sle_->at(sfMaxFee);
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfMaxFee is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasMaxFee() const
+    {
+        return this->sle_->isFieldPresent(sfMaxFee);
+    }
+
+    /**
+     * @brief Get sfRemainingOwnerCount (SoeDefault)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_UINT32::type::value_type>
+    getRemainingOwnerCount() const
+    {
+        if (hasRemainingOwnerCount())
+            return this->sle_->at(sfRemainingOwnerCount);
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfRemainingOwnerCount is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasRemainingOwnerCount() const
+    {
+        return this->sle_->isFieldPresent(sfRemainingOwnerCount);
+    }
+
+    /**
+     * @brief Get sfOwnerNode (SoeRequired)
+     * @return The field value.
+     */
+    [[nodiscard]]
+    SF_UINT64::type::value_type
+    getOwnerNode() const
+    {
+        return this->sle_->at(sfOwnerNode);
+    }
+
+    /**
+     * @brief Get sfSponseeNode (SoeRequired)
+     * @return The field value.
+     */
+    [[nodiscard]]
+    SF_UINT64::type::value_type
+    getSponseeNode() const
+    {
+        return this->sle_->at(sfSponseeNode);
+    }
+};
+
+/**
+ * @brief Builder for Sponsorship ledger entries.
+ *
+ * Provides a fluent interface for constructing ledger entries with method chaining.
+ * Uses STObject internally for flexible ledger entry construction.
+ * Inherits common field setters from LedgerEntryBuilderBase.
+ */
+class SponsorshipBuilder : public LedgerEntryBuilderBase<SponsorshipBuilder>
+{
+public:
+    /**
+     * @brief Construct a new SponsorshipBuilder with required fields.
+     * @param previousTxnID The sfPreviousTxnID field value.
+     * @param previousTxnLgrSeq The sfPreviousTxnLgrSeq field value.
+     * @param owner The sfOwner field value.
+     * @param sponsee The sfSponsee field value.
+     * @param ownerNode The sfOwnerNode field value.
+     * @param sponseeNode The sfSponseeNode field value.
+     */
+    SponsorshipBuilder(std::decay_t<typename SF_UINT256::type::value_type> const& previousTxnID,std::decay_t<typename SF_UINT32::type::value_type> const& previousTxnLgrSeq,std::decay_t<typename SF_ACCOUNT::type::value_type> const& owner,std::decay_t<typename SF_ACCOUNT::type::value_type> const& sponsee,std::decay_t<typename SF_UINT64::type::value_type> const& ownerNode,std::decay_t<typename SF_UINT64::type::value_type> const& sponseeNode)
+        : LedgerEntryBuilderBase<SponsorshipBuilder>(ltSPONSORSHIP)
+    {
+        setPreviousTxnID(previousTxnID);
+        setPreviousTxnLgrSeq(previousTxnLgrSeq);
+        setOwner(owner);
+        setSponsee(sponsee);
+        setOwnerNode(ownerNode);
+        setSponseeNode(sponseeNode);
+    }
+
+    /**
+     * @brief Construct a SponsorshipBuilder from an existing SLE object.
+     * @param sle The existing ledger entry to copy from.
+     * @throws std::runtime_error if the ledger entry type doesn't match.
+     */
+    SponsorshipBuilder(SLE::const_pointer sle)
+    {
+        if (sle->at(sfLedgerEntryType) != ltSPONSORSHIP)
+        {
+            throw std::runtime_error("Invalid ledger entry type for Sponsorship");
+        }
+        object_ = *sle;
+    }
+
+    /** @brief Ledger entry-specific field setters */
+
+    /**
+     * @brief Set sfPreviousTxnID (SoeRequired)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipBuilder&
+    setPreviousTxnID(std::decay_t<typename SF_UINT256::type::value_type> const& value)
+    {
+        object_[sfPreviousTxnID] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfPreviousTxnLgrSeq (SoeRequired)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipBuilder&
+    setPreviousTxnLgrSeq(std::decay_t<typename SF_UINT32::type::value_type> const& value)
+    {
+        object_[sfPreviousTxnLgrSeq] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfOwner (SoeRequired)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipBuilder&
+    setOwner(std::decay_t<typename SF_ACCOUNT::type::value_type> const& value)
+    {
+        object_[sfOwner] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfSponsee (SoeRequired)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipBuilder&
+    setSponsee(std::decay_t<typename SF_ACCOUNT::type::value_type> const& value)
+    {
+        object_[sfSponsee] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfFeeAmount (SoeOptional)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipBuilder&
+    setFeeAmount(std::decay_t<typename SF_AMOUNT::type::value_type> const& value)
+    {
+        object_[sfFeeAmount] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfMaxFee (SoeOptional)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipBuilder&
+    setMaxFee(std::decay_t<typename SF_AMOUNT::type::value_type> const& value)
+    {
+        object_[sfMaxFee] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfRemainingOwnerCount (SoeDefault)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipBuilder&
+    setRemainingOwnerCount(std::decay_t<typename SF_UINT32::type::value_type> const& value)
+    {
+        object_[sfRemainingOwnerCount] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfOwnerNode (SoeRequired)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipBuilder&
+    setOwnerNode(std::decay_t<typename SF_UINT64::type::value_type> const& value)
+    {
+        object_[sfOwnerNode] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfSponseeNode (SoeRequired)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipBuilder&
+    setSponseeNode(std::decay_t<typename SF_UINT64::type::value_type> const& value)
+    {
+        object_[sfSponseeNode] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Build and return the completed Sponsorship wrapper.
+     * @param index The ledger entry index.
+     * @return The constructed ledger entry wrapper.
+     */
+    Sponsorship
+    build(uint256 const& index)
+    {
+        return Sponsorship{std::make_shared<SLE>(std::move(object_), index)};
+    }
+};
+
+}  // namespace xrpl::ledger_entries

include/xrpl/protocol_autogen/transactions/SponsorshipSet.h

@@ -0,0 +1,290 @@
+// This file is auto-generated. Do not edit.
+#pragma once
+
+#include <xrpl/protocol/STTx.h>
+#include <xrpl/protocol/STParsedJSON.h>
+#include <xrpl/protocol/jss.h>
+#include <xrpl/protocol_autogen/TransactionBase.h>
+#include <xrpl/protocol_autogen/TransactionBuilderBase.h>
+#include <xrpl/json/json_value.h>
+
+#include <stdexcept>
+#include <optional>
+
+namespace xrpl::transactions {
+
+class SponsorshipSetBuilder;
+
+/**
+ * @brief Transaction: SponsorshipSet
+ *
+ * Type: ttSPONSORSHIP_SET (91)
+ * Delegable: Delegation::Delegable
+ * Amendment: featureSponsor
+ * Privileges: NoPriv
+ *
+ * Immutable wrapper around STTx providing type-safe field access.
+ * Use SponsorshipSetBuilder to construct new transactions.
+ */
+class SponsorshipSet : public TransactionBase
+{
+public:
+    static constexpr xrpl::TxType txType = ttSPONSORSHIP_SET;
+
+    /**
+     * @brief Construct a SponsorshipSet transaction wrapper from an existing STTx object.
+     * @throws std::runtime_error if the transaction type doesn't match.
+     */
+    explicit SponsorshipSet(std::shared_ptr<STTx const> tx)
+        : TransactionBase(std::move(tx))
+    {
+        // Verify transaction type
+        if (tx_->getTxnType() != txType)
+        {
+            throw std::runtime_error("Invalid transaction type for SponsorshipSet");
+        }
+    }
+
+    // Transaction-specific field getters
+
+    /**
+     * @brief Get sfCounterpartySponsor (SoeOptional)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_ACCOUNT::type::value_type>
+    getCounterpartySponsor() const
+    {
+        if (hasCounterpartySponsor())
+        {
+            return this->tx_->at(sfCounterpartySponsor);
+        }
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfCounterpartySponsor is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasCounterpartySponsor() const
+    {
+        return this->tx_->isFieldPresent(sfCounterpartySponsor);
+    }
+
+    /**
+     * @brief Get sfSponsee (SoeOptional)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_ACCOUNT::type::value_type>
+    getSponsee() const
+    {
+        if (hasSponsee())
+        {
+            return this->tx_->at(sfSponsee);
+        }
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfSponsee is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasSponsee() const
+    {
+        return this->tx_->isFieldPresent(sfSponsee);
+    }
+
+    /**
+     * @brief Get sfFeeAmount (SoeOptional)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_AMOUNT::type::value_type>
+    getFeeAmount() const
+    {
+        if (hasFeeAmount())
+        {
+            return this->tx_->at(sfFeeAmount);
+        }
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfFeeAmount is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasFeeAmount() const
+    {
+        return this->tx_->isFieldPresent(sfFeeAmount);
+    }
+
+    /**
+     * @brief Get sfMaxFee (SoeOptional)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_AMOUNT::type::value_type>
+    getMaxFee() const
+    {
+        if (hasMaxFee())
+        {
+            return this->tx_->at(sfMaxFee);
+        }
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfMaxFee is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasMaxFee() const
+    {
+        return this->tx_->isFieldPresent(sfMaxFee);
+    }
+
+    /**
+     * @brief Get sfRemainingOwnerCount (SoeOptional)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_UINT32::type::value_type>
+    getRemainingOwnerCount() const
+    {
+        if (hasRemainingOwnerCount())
+        {
+            return this->tx_->at(sfRemainingOwnerCount);
+        }
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfRemainingOwnerCount is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasRemainingOwnerCount() const
+    {
+        return this->tx_->isFieldPresent(sfRemainingOwnerCount);
+    }
+};
+
+/**
+ * @brief Builder for SponsorshipSet transactions.
+ *
+ * Provides a fluent interface for constructing transactions with method chaining.
+ * Uses STObject internally for flexible transaction construction.
+ * Inherits common field setters from TransactionBuilderBase.
+ */
+class SponsorshipSetBuilder : public TransactionBuilderBase<SponsorshipSetBuilder>
+{
+public:
+    /**
+     * @brief Construct a new SponsorshipSetBuilder with required fields.
+     * @param account The account initiating the transaction.
+     * @param sequence Optional sequence number for the transaction.
+     * @param fee Optional fee for the transaction.
+     */
+    SponsorshipSetBuilder(SF_ACCOUNT::type::value_type account,
+                    std::optional<SF_UINT32::type::value_type> sequence = std::nullopt,
+                    std::optional<SF_AMOUNT::type::value_type> fee = std::nullopt
+)
+        : TransactionBuilderBase<SponsorshipSetBuilder>(ttSPONSORSHIP_SET, account, sequence, fee)
+    {
+    }
+
+    /**
+     * @brief Construct a SponsorshipSetBuilder from an existing STTx object.
+     * @param tx The existing transaction to copy from.
+     * @throws std::runtime_error if the transaction type doesn't match.
+     */
+    SponsorshipSetBuilder(std::shared_ptr<STTx const> tx)
+    {
+        if (tx->getTxnType() != ttSPONSORSHIP_SET)
+        {
+            throw std::runtime_error("Invalid transaction type for SponsorshipSetBuilder");
+        }
+        object_ = *tx;
+    }
+
+    /** @brief Transaction-specific field setters */
+
+    /**
+     * @brief Set sfCounterpartySponsor (SoeOptional)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipSetBuilder&
+    setCounterpartySponsor(std::decay_t<typename SF_ACCOUNT::type::value_type> const& value)
+    {
+        object_[sfCounterpartySponsor] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfSponsee (SoeOptional)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipSetBuilder&
+    setSponsee(std::decay_t<typename SF_ACCOUNT::type::value_type> const& value)
+    {
+        object_[sfSponsee] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfFeeAmount (SoeOptional)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipSetBuilder&
+    setFeeAmount(std::decay_t<typename SF_AMOUNT::type::value_type> const& value)
+    {
+        object_[sfFeeAmount] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfMaxFee (SoeOptional)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipSetBuilder&
+    setMaxFee(std::decay_t<typename SF_AMOUNT::type::value_type> const& value)
+    {
+        object_[sfMaxFee] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfRemainingOwnerCount (SoeOptional)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipSetBuilder&
+    setRemainingOwnerCount(std::decay_t<typename SF_UINT32::type::value_type> const& value)
+    {
+        object_[sfRemainingOwnerCount] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Build and return the SponsorshipSet wrapper.
+     * @param publicKey The public key for signing.
+     * @param secretKey The secret key for signing.
+     * @return The constructed transaction wrapper.
+     */
+    SponsorshipSet
+    build(PublicKey const& publicKey, SecretKey const& secretKey)
+    {
+        sign(publicKey, secretKey);
+        return SponsorshipSet{std::make_shared<STTx>(std::move(object_))};
+    }
+};
+
+}  // namespace xrpl::transactions

include/xrpl/protocol_autogen/transactions/SponsorshipTransfer.h

@@ -0,0 +1,179 @@
+// This file is auto-generated. Do not edit.
+#pragma once
+
+#include <xrpl/protocol/STTx.h>
+#include <xrpl/protocol/STParsedJSON.h>
+#include <xrpl/protocol/jss.h>
+#include <xrpl/protocol_autogen/TransactionBase.h>
+#include <xrpl/protocol_autogen/TransactionBuilderBase.h>
+#include <xrpl/json/json_value.h>
+
+#include <stdexcept>
+#include <optional>
+
+namespace xrpl::transactions {
+
+class SponsorshipTransferBuilder;
+
+/**
+ * @brief Transaction: SponsorshipTransfer
+ *
+ * Type: ttSPONSORSHIP_TRANSFER (90)
+ * Delegable: Delegation::NotDelegable
+ * Amendment: featureSponsor
+ * Privileges: NoPriv
+ *
+ * Immutable wrapper around STTx providing type-safe field access.
+ * Use SponsorshipTransferBuilder to construct new transactions.
+ */
+class SponsorshipTransfer : public TransactionBase
+{
+public:
+    static constexpr xrpl::TxType txType = ttSPONSORSHIP_TRANSFER;
+
+    /**
+     * @brief Construct a SponsorshipTransfer transaction wrapper from an existing STTx object.
+     * @throws std::runtime_error if the transaction type doesn't match.
+     */
+    explicit SponsorshipTransfer(std::shared_ptr<STTx const> tx)
+        : TransactionBase(std::move(tx))
+    {
+        // Verify transaction type
+        if (tx_->getTxnType() != txType)
+        {
+            throw std::runtime_error("Invalid transaction type for SponsorshipTransfer");
+        }
+    }
+
+    // Transaction-specific field getters
+
+    /**
+     * @brief Get sfObjectID (SoeOptional)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_UINT256::type::value_type>
+    getObjectID() const
+    {
+        if (hasObjectID())
+        {
+            return this->tx_->at(sfObjectID);
+        }
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfObjectID is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasObjectID() const
+    {
+        return this->tx_->isFieldPresent(sfObjectID);
+    }
+
+    /**
+     * @brief Get sfSponsee (SoeOptional)
+     * @return The field value, or std::nullopt if not present.
+     */
+    [[nodiscard]]
+    protocol_autogen::Optional<SF_ACCOUNT::type::value_type>
+    getSponsee() const
+    {
+        if (hasSponsee())
+        {
+            return this->tx_->at(sfSponsee);
+        }
+        return std::nullopt;
+    }
+
+    /**
+     * @brief Check if sfSponsee is present.
+     * @return True if the field is present, false otherwise.
+     */
+    [[nodiscard]]
+    bool
+    hasSponsee() const
+    {
+        return this->tx_->isFieldPresent(sfSponsee);
+    }
+};
+
+/**
+ * @brief Builder for SponsorshipTransfer transactions.
+ *
+ * Provides a fluent interface for constructing transactions with method chaining.
+ * Uses STObject internally for flexible transaction construction.
+ * Inherits common field setters from TransactionBuilderBase.
+ */
+class SponsorshipTransferBuilder : public TransactionBuilderBase<SponsorshipTransferBuilder>
+{
+public:
+    /**
+     * @brief Construct a new SponsorshipTransferBuilder with required fields.
+     * @param account The account initiating the transaction.
+     * @param sequence Optional sequence number for the transaction.
+     * @param fee Optional fee for the transaction.
+     */
+    SponsorshipTransferBuilder(SF_ACCOUNT::type::value_type account,
+                    std::optional<SF_UINT32::type::value_type> sequence = std::nullopt,
+                    std::optional<SF_AMOUNT::type::value_type> fee = std::nullopt
+)
+        : TransactionBuilderBase<SponsorshipTransferBuilder>(ttSPONSORSHIP_TRANSFER, account, sequence, fee)
+    {
+    }
+
+    /**
+     * @brief Construct a SponsorshipTransferBuilder from an existing STTx object.
+     * @param tx The existing transaction to copy from.
+     * @throws std::runtime_error if the transaction type doesn't match.
+     */
+    SponsorshipTransferBuilder(std::shared_ptr<STTx const> tx)
+    {
+        if (tx->getTxnType() != ttSPONSORSHIP_TRANSFER)
+        {
+            throw std::runtime_error("Invalid transaction type for SponsorshipTransferBuilder");
+        }
+        object_ = *tx;
+    }
+
+    /** @brief Transaction-specific field setters */
+
+    /**
+     * @brief Set sfObjectID (SoeOptional)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipTransferBuilder&
+    setObjectID(std::decay_t<typename SF_UINT256::type::value_type> const& value)
+    {
+        object_[sfObjectID] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Set sfSponsee (SoeOptional)
+     * @return Reference to this builder for method chaining.
+     */
+    SponsorshipTransferBuilder&
+    setSponsee(std::decay_t<typename SF_ACCOUNT::type::value_type> const& value)
+    {
+        object_[sfSponsee] = value;
+        return *this;
+    }
+
+    /**
+     * @brief Build and return the SponsorshipTransfer wrapper.
+     * @param publicKey The public key for signing.
+     * @param secretKey The secret key for signing.
+     * @return The constructed transaction wrapper.
+     */
+    SponsorshipTransfer
+    build(PublicKey const& publicKey, SecretKey const& secretKey)
+    {
+        sign(publicKey, secretKey);
+        return SponsorshipTransfer{std::make_shared<STTx>(std::move(object_))};
+    }
+};
+
+}  // namespace xrpl::transactions

include/xrpl/tx/ApplyContext.h

@@ -127,6 +127,15 @@ public:
     TER
     checkInvariants(TER const result, XRPAmount const fee);
 
+    ApplyViewContext
+    getApplyViewContext()
+    {
+        XRPL_ASSERT(
+            view_.has_value(),
+            "xrpl::ApplyContext::getApplyViewContext : view_ emplaced in constructor");
+        return {.view = *view_, .tx = tx};
+    }
+
 private:
     static TER
     failInvariantCheck(TER const result);

include/xrpl/tx/Transactor.h

@@ -10,8 +10,10 @@
 #include <xrpl/ledger/ReadView.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Fees.h>
+#include <xrpl/protocol/Keylet.h>
 #include <xrpl/protocol/Permissions.h>
 #include <xrpl/protocol/Rules.h>
+#include <xrpl/protocol/SField.h>
 #include <xrpl/protocol/STObject.h>
 #include <xrpl/protocol/TER.h>
 #include <xrpl/protocol/Units.h>
@@ -126,6 +128,21 @@ struct PreflightResult;
 // Needed for preflight specialization
 class Change;
 
+enum class FeePayerType {
+    Account,
+    Delegate,
+    SponsorCoSigned,
+    SponsorPreFunded,
+};
+
+struct FeePayer
+{
+    AccountID id;
+    Keylet keylet;
+    SF_AMOUNT const& balanceField;
+    FeePayerType type{FeePayerType::Account};
+};
+
 class Transactor
 {
 protected:
@@ -298,6 +315,10 @@ public:
 
         return T::checkGranularSemantics(view, tx, heldGranularPermissions);
     }
+
+    static NotTEC
+    checkSponsor(ReadView const& view, STTx const& tx);
+
     /////////////////////////////////////////////////////
 
     // Interface used by AccountDelete
@@ -459,6 +480,9 @@ private:
     std::pair<TER, XRPAmount>
     reset(XRPAmount fee);
 
+    static FeePayer
+    getFeePayer(ReadView const& view, STTx const& tx);
+
     TER
     consumeSeqProxy(SLE::pointer const& sleAccount);
     TER

include/xrpl/tx/invariants/InvariantCheck.h

@@ -15,6 +15,7 @@
 #include <xrpl/tx/invariants/NFTInvariant.h>
 #include <xrpl/tx/invariants/PermissionedDEXInvariant.h>
 #include <xrpl/tx/invariants/PermissionedDomainInvariant.h>
+#include <xrpl/tx/invariants/SponsorshipInvariant.h>
 #include <xrpl/tx/invariants/VaultInvariant.h>
 
 #include <cstdint>
@@ -441,7 +442,9 @@ using InvariantChecks = std::tuple<
     ValidMPTPayment,
     ValidAmounts,
     ValidMPTTransfer,
-    ObjectHasPseudoAccount>;
+    ObjectHasPseudoAccount,
+    SponsorshipOwnerCountsMatch,
+    SponsorshipAccountCountMatchesField>;
 
 /**
  * @brief get a tuple of all invariant checks

include/xrpl/tx/invariants/SponsorshipInvariant.h

@@ -0,0 +1,61 @@
+#pragma once
+
+#include <xrpl/beast/utility/Journal.h>
+#include <xrpl/ledger/ReadView.h>
+#include <xrpl/protocol/STLedgerEntry.h>
+#include <xrpl/protocol/STTx.h>
+#include <xrpl/protocol/TER.h>
+#include <xrpl/protocol/XRPAmount.h>
+
+#include <cstdint>
+
+namespace xrpl {
+
+/**
+ * @brief Invariant: Sponsored owner counts are balanced.
+ *
+ * The following checks are made for every transaction:
+ *  - The sum of all per-account deltas of `sfSponsoredOwnerCount` equals
+ *    the sum of all per-account deltas of `sfSponsoringOwnerCount`.
+ *  - Account OwnerCount must be greater than or equal to SponsoredOwnerCount.
+ *  - The net delta of sponsored object owner counts (the owner-count
+ *    magnitude of sponsored ledger entries) equals the net delta of
+ *    `sfSponsoredOwnerCount`.
+ */
+class SponsorshipOwnerCountsMatch
+{
+    std::int64_t deltaSponsoredOwnerCount_ = 0;
+    std::int64_t deltaSponsoringOwnerCount_ = 0;
+    std::int64_t deltaSponsoredObjectOwnerCount_ = 0;
+    std::uint64_t ownerCountBelowSponsored_ = 0;
+
+public:
+    void
+    visitEntry(bool, SLE::const_ref, SLE::const_ref);
+
+    [[nodiscard]] bool
+    finalize(STTx const&, TER const, XRPAmount const, ReadView const&, beast::Journal const&) const;
+};
+
+/**
+ * @brief Invariant: Sponsoring account relationships tracked consistently.
+ *
+ * The following check is made for every transaction:
+ *  - The net delta of `sfSponsoringAccountCount` across all accounts equals
+ *    the net delta of the count of ltACCOUNT_ROOT entries having
+ *    `sfSponsor` present (presence transitions only: add/remove).
+ */
+class SponsorshipAccountCountMatchesField
+{
+    std::int64_t deltaSponsoringAccountCount_ = 0;
+    std::int64_t deltaSponsorFieldPresence_ = 0;
+
+public:
+    void
+    visitEntry(bool, SLE::const_ref, SLE::const_ref);
+
+    [[nodiscard]] bool
+    finalize(STTx const&, TER const, XRPAmount const, ReadView const&, beast::Journal const&) const;
+};
+
+}  // namespace xrpl

include/xrpl/tx/paths/AMMOffer.h

@@ -7,6 +7,7 @@
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Concepts.h>
 #include <xrpl/protocol/Quality.h>
+#include <xrpl/protocol/STLedgerEntry.h>
 #include <xrpl/protocol/TER.h>
 
 #include <cstdint>
@@ -110,7 +111,10 @@ public:
     send(Args&&... args)
     {
         return accountSend(
-            std::forward<Args>(args)..., WaiveTransferFee::Yes, AllowMPTOverflow::Yes);
+            std::forward<Args>(args)...,
+            SLE::pointer(),
+            WaiveTransferFee::Yes,
+            AllowMPTOverflow::Yes);
     }
 
     [[nodiscard]] bool

include/xrpl/tx/paths/Offer.h

@@ -234,7 +234,8 @@ template <typename... Args>
 TER
 TOffer<TIn, TOut>::send(Args&&... args)
 {
-    return accountSend(std::forward<Args>(args)..., WaiveTransferFee::No, AllowMPTOverflow::Yes);
+    return accountSend(
+        std::forward<Args>(args)..., SLE::pointer(), WaiveTransferFee::No, AllowMPTOverflow::Yes);
 }
 
 template <StepAmount TIn, StepAmount TOut>

include/xrpl/tx/transactors/sponsor/SponsorshipSet.h

@@ -0,0 +1,52 @@
+#pragma once
+
+#include <xrpl/beast/utility/Journal.h>
+#include <xrpl/ledger/ReadView.h>
+#include <xrpl/protocol/STLedgerEntry.h>
+#include <xrpl/protocol/STTx.h>
+#include <xrpl/protocol/TER.h>
+#include <xrpl/protocol/XRPAmount.h>
+#include <xrpl/tx/ApplyContext.h>
+#include <xrpl/tx/Transactor.h>
+
+#include <cstdint>
+
+namespace xrpl {
+
+class SponsorshipSet : public Transactor
+{
+public:
+    static constexpr auto kConsequencesFactory = ConsequencesFactoryType::Normal;
+
+    explicit SponsorshipSet(ApplyContext& ctx) : Transactor(ctx)
+    {
+    }
+
+    static TxConsequences
+    makeTxConsequences(PreflightContext const& ctx);
+
+    static std::uint32_t
+    getFlagsMask(PreflightContext const& ctx);
+
+    static NotTEC
+    preflight(PreflightContext const& ctx);
+
+    static TER
+    preclaim(PreclaimContext const& ctx);
+
+    TER
+    doApply() override;
+
+    void
+    visitInvariantEntry(bool isDelete, SLE::const_ref before, SLE::const_ref after) override;
+
+    [[nodiscard]] bool
+    finalizeInvariants(
+        STTx const& tx,
+        TER result,
+        XRPAmount fee,
+        ReadView const& view,
+        beast::Journal const& j) override;
+};
+
+}  // namespace xrpl

include/xrpl/tx/transactors/sponsor/SponsorshipTransfer.h

@@ -0,0 +1,49 @@
+#pragma once
+
+#include <xrpl/beast/utility/Journal.h>
+#include <xrpl/ledger/ReadView.h>
+#include <xrpl/protocol/STLedgerEntry.h>
+#include <xrpl/protocol/STTx.h>
+#include <xrpl/protocol/TER.h>
+#include <xrpl/protocol/XRPAmount.h>
+#include <xrpl/tx/ApplyContext.h>
+#include <xrpl/tx/Transactor.h>
+
+#include <cstdint>
+
+namespace xrpl {
+
+class SponsorshipTransfer : public Transactor
+{
+public:
+    static constexpr auto kConsequencesFactory = ConsequencesFactoryType::Normal;
+
+    explicit SponsorshipTransfer(ApplyContext& ctx) : Transactor(ctx)
+    {
+    }
+
+    static std::uint32_t
+    getFlagsMask(PreflightContext const& ctx);
+
+    static NotTEC
+    preflight(PreflightContext const& ctx);
+
+    static TER
+    preclaim(PreclaimContext const& ctx);
+
+    TER
+    doApply() override;
+
+    void
+    visitInvariantEntry(bool isDelete, SLE::const_ref before, SLE::const_ref after) override;
+
+    [[nodiscard]] bool
+    finalizeInvariants(
+        STTx const& tx,
+        TER result,
+        XRPAmount fee,
+        ReadView const& view,
+        beast::Journal const& j) override;
+};
+
+}  // namespace xrpl

include/xrpl/tx/transactors/token/MPTokenIssuanceCreate.h

@@ -76,7 +76,7 @@ public:
         beast::Journal const& j) override;
 
     static std::expected<MPTID, TER>
-    create(ApplyView& view, beast::Journal journal, MPTCreateArgs const& args);
+    create(ApplyViewContext ctx, beast::Journal journal, MPTCreateArgs const& args);
 };
 
 }  // namespace xrpl

src/libxrpl/ledger/PaymentSandbox.cpp

@@ -3,6 +3,7 @@
 #include <xrpl/basics/base_uint.h>
 #include <xrpl/beast/utility/Zero.h>
 #include <xrpl/beast/utility/instrumentation.h>
+#include <xrpl/ledger/OwnerCounts.h>
 #include <xrpl/ledger/RawView.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Issue.h>
@@ -170,7 +171,7 @@ DeferredCredits::issuerSelfDebitMPT(
 }
 
 void
-DeferredCredits::ownerCount(AccountID const& id, std::uint32_t cur, std::uint32_t next)
+DeferredCredits::ownerCount(AccountID const& id, OwnerCounts const& cur, OwnerCounts const& next)
 {
     auto const v = std::max(cur, next);
     auto r = ownerCounts_.emplace(id, v);
@@ -181,7 +182,7 @@ DeferredCredits::ownerCount(AccountID const& id, std::uint32_t cur, std::uint32_
     }
 }
 
-std::optional<std::uint32_t>
+std::optional<OwnerCounts>
 DeferredCredits::ownerCount(AccountID const& id) const
 {
     auto i = ownerCounts_.find(id);
@@ -391,10 +392,10 @@ PaymentSandbox::balanceHookSelfIssueMPT(xrpl::MPTIssue const& issue, std::int64_
     return STAmount{issue};
 }
 
-std::uint32_t
-PaymentSandbox::ownerCountHook(AccountID const& account, std::uint32_t count) const
+OwnerCounts
+PaymentSandbox::ownerCountHook(AccountID const& account, OwnerCounts const& count) const
 {
-    std::uint32_t result = count;
+    OwnerCounts result = count;
     for (auto curSB = this; curSB != nullptr; curSB = curSB->ps_)
     {
         if (auto adj = curSB->tab_.ownerCount(account))
@@ -442,8 +443,8 @@ PaymentSandbox::issuerSelfDebitHookMPT(
 void
 PaymentSandbox::adjustOwnerCountHook(
     AccountID const& account,
-    std::uint32_t cur,
-    std::uint32_t next)
+    OwnerCounts const& cur,
+    OwnerCounts const& next)
 {
     tab_.ownerCount(account, cur, next);
 }

src/libxrpl/ledger/View.cpp

@@ -14,6 +14,7 @@
 #include <xrpl/ledger/helpers/DirectoryHelpers.h>
 #include <xrpl/ledger/helpers/MPTokenHelpers.h>
 #include <xrpl/ledger/helpers/RippleStateHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/ledger/helpers/TokenHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Asset.h>
@@ -431,8 +432,7 @@ canWithdraw(ReadView const& view, STTx const& tx)
 
 TER
 doWithdraw(
-    ApplyView& view,
-    STTx const& tx,
+    ApplyViewContext ctx,
     AccountID const& senderAcct,
     AccountID const& dstAcct,
     AccountID const& sourceAcct,
@@ -440,23 +440,24 @@ doWithdraw(
     STAmount const& amount,
     beast::Journal j)
 {
+    auto const dstSle = ctx.view.read(keylet::account(dstAcct));
+
     // Create trust line or MPToken for the receiving account
     if (dstAcct == senderAcct)
     {
-        if (auto const ter = addEmptyHolding(view, senderAcct, priorBalance, amount.asset(), j);
+        if (auto const ter = addEmptyHolding(ctx, senderAcct, priorBalance, amount.asset(), j);
             !isTesSuccess(ter) && ter != tecDUPLICATE)
             return ter;
     }
     else
     {
-        auto dstSle = view.read(keylet::account(dstAcct));
-        if (auto err = verifyDepositPreauth(tx, view, senderAcct, dstAcct, dstSle, j))
+        if (auto err = verifyDepositPreauth(ctx.tx, ctx.view, senderAcct, dstAcct, dstSle, j))
             return err;
     }
 
     // Sanity check
     if (accountHolds(
-            view,
+            ctx.view,
             sourceAcct,
             amount.asset(),
             FreezeHandling::IgnoreFreeze,
@@ -469,9 +470,18 @@ doWithdraw(
         // LCOV_EXCL_STOP
     }
 
+    // A reserve sponsor only covers tx.Account's own objects, so resolve the
+    // sponsor against the destination. accountSend can auto-create a holding
+    // for dstAcct; keying on the destination ensures a third-party destination's
+    // holding is never stamped with the tx's reserve sponsor.
+    auto const sponsorSle = getEffectiveTxReserveSponsor(ctx, dstSle);
+    if (!sponsorSle)
+        return sponsorSle.error();  // LCOV_EXCL_LINE
+
     // Move the funds directly from the broker's pseudo-account to the
     // dstAcct
-    return accountSend(view, sourceAcct, dstAcct, amount, j, WaiveTransferFee::Yes);
+    return accountSend(
+        ctx.view, sourceAcct, dstAcct, amount, j, *sponsorSle, WaiveTransferFee::Yes);
 }
 
 TER

src/libxrpl/ledger/helpers/AccountRootHelpers.cpp

@@ -7,7 +7,9 @@
 #include <xrpl/beast/utility/Zero.h>
 #include <xrpl/beast/utility/instrumentation.h>
 #include <xrpl/ledger/ApplyView.h>
+#include <xrpl/ledger/OwnerCounts.h>
 #include <xrpl/ledger/ReadView.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Feature.h>
 #include <xrpl/protocol/Indexes.h>
@@ -15,6 +17,7 @@
 #include <xrpl/protocol/Rate.h>
 #include <xrpl/protocol/SField.h>
 #include <xrpl/protocol/STLedgerEntry.h>
+#include <xrpl/protocol/STTx.h>
 #include <xrpl/protocol/TER.h>
 #include <xrpl/protocol/XRPAmount.h>
 #include <xrpl/protocol/digest.h>
@@ -41,46 +44,226 @@ isGlobalFrozen(ReadView const& view, AccountID const& issuer)
     return false;
 }
 
+namespace {
+
 // An owner count cannot be negative. If adjustment would cause a negative
 // owner count, clamp the owner count at 0. Similarly for overflow. This
 // adjustment allows the ownerCount to be adjusted up or down in multiple steps.
 // If id != std::nullopt, then do error reporting.
 //
 // Returns adjusted owner count.
-static std::uint32_t
+std::uint32_t
 confineOwnerCount(
-    std::uint32_t current,
-    std::int32_t adjustment,
+    std::uint32_t currentOwnerCount,
+    std::int32_t ownerCountAdj,
     std::optional<AccountID> const& id = std::nullopt,
     beast::Journal j = beast::Journal{beast::Journal::getNullSink()})
 {
-    std::uint32_t adjusted{current + adjustment};
-    if (adjustment > 0)
+    std::uint32_t totalOwnerCount{currentOwnerCount + ownerCountAdj};
+    if (ownerCountAdj > 0)
     {
         // Overflow is well defined on unsigned
-        if (adjusted < current)
+        if (totalOwnerCount < currentOwnerCount)
         {
+            // LCOV_EXCL_START
             if (id)
             {
                 JLOG(j.fatal()) << "Account " << *id << " owner count exceeds max!";
             }
-            adjusted = std::numeric_limits<std::uint32_t>::max();
+            totalOwnerCount = std::numeric_limits<std::uint32_t>::max();
+            // LCOV_EXCL_STOP
         }
     }
     else
     {
         // Underflow is well defined on unsigned
-        if (adjusted > current)
+        if (totalOwnerCount > currentOwnerCount)
         {
+            // LCOV_EXCL_START
             if (id)
             {
                 JLOG(j.fatal()) << "Account " << *id << " owner count set below 0!";
             }
-            adjusted = 0;
+            totalOwnerCount = 0;
             XRPL_ASSERT(!id, "xrpl::confineOwnerCount : id is not set");
+            // LCOV_EXCL_STOP
         }
     }
-    return adjusted;
+    return totalOwnerCount;
+}
+
+// Returns the number of account reserves funded by this account: 1 for itself (0 if sponsored by
+// another account) plus the count of accounts it sponsors.
+std::uint32_t
+accountCountImpl(SLE::const_ref sle, std::int32_t accountCountAdj, beast::Journal j)
+{
+    bool const isSponsored = sle->isFieldPresent(sfSponsor);
+    std::int64_t const sponsoringAccountCount = sle->getFieldU32(sfSponsoringAccountCount);
+    std::int64_t const currentAccountCount = (isSponsored ? 0 : 1) + sponsoringAccountCount;
+
+    std::int64_t totalAccountCount{currentAccountCount + accountCountAdj};
+    if (totalAccountCount > std::numeric_limits<std::uint32_t>::max())
+    {
+        // LCOV_EXCL_START
+        JLOG(j.fatal()) << "Reserve count exceeds max!";
+        totalAccountCount = std::numeric_limits<std::uint32_t>::max();
+        // LCOV_EXCL_STOP
+    }
+    else if (totalAccountCount < 0)
+    {
+        // LCOV_EXCL_START
+        UNREACHABLE("xrpl::accountCountImpl : Reserve count set below 0");
+        JLOG(j.fatal()) << "Reserve count set below 0";
+        totalAccountCount = 0;
+        // LCOV_EXCL_STOP
+    }
+
+    return totalAccountCount;
+}
+
+std::uint32_t
+adjustOwnerCountImpl(
+    ApplyView& view,
+    SLE::ref sle,
+    SF_UINT32 const& sfield,
+    AccountID const& accID,
+    std::int32_t ownerCountAdj,
+    beast::Journal j)
+{
+    std::uint32_t const currentOwnerCount = sle->at(sfield);
+    std::uint32_t const totalOwnerCount =
+        confineOwnerCount(currentOwnerCount, ownerCountAdj, accID, j);
+    sle->at(sfield) = totalOwnerCount;
+    view.update(sle);
+    return totalOwnerCount;
+}
+
+void
+adjustOwnerCountSigned(
+    ApplyView& view,
+    SLE::ref accountSle,
+    SLE::ref sponsorSle,
+    std::int32_t adjustment,
+    beast::Journal j)
+{
+    if (view.rules().enabled(featureSponsor))
+    {
+        XRPL_ASSERT(accountSle, "xrpl::adjustOwnerCountSigned : valid account sle");
+        if (!accountSle)
+            return;  // LCOV_EXCL_LINE
+
+        auto const accountID = accountSle->getAccountID(sfAccount);
+        bool const validType = accountSle->getType() == ltACCOUNT_ROOT;
+        XRPL_ASSERT(validType, "xrpl::adjustOwnerCountSigned : valid account sle type");
+        if (!validType)
+            return;  // LCOV_EXCL_LINE
+
+        XRPL_ASSERT(adjustment, "xrpl::adjustOwnerCountSigned : nonzero adjustment input");
+
+        OwnerCounts const currentOwnerCount(accountSle);
+        OwnerCounts totalOwnerCount(currentOwnerCount);
+
+        if (sponsorSle)
+        {
+            bool const validSponsorType = sponsorSle->getType() == ltACCOUNT_ROOT;
+            XRPL_ASSERT(validSponsorType, "xrpl::adjustOwnerCountSigned : valid sponsor sle type");
+            if (!validSponsorType)
+                return;  // LCOV_EXCL_LINE
+            auto const sponsorID = sponsorSle->getAccountID(sfAccount);
+
+            totalOwnerCount.sponsored = adjustOwnerCountImpl(
+                view, accountSle, sfSponsoredOwnerCount, accountID, adjustment, j);
+
+            {
+                OwnerCounts const sponsorCurrent(sponsorSle);
+                OwnerCounts sponsorAdjustment(sponsorCurrent);
+                sponsorAdjustment.sponsoring = adjustOwnerCountImpl(
+                    view, sponsorSle, sfSponsoringOwnerCount, sponsorID, adjustment, j);
+                view.adjustOwnerCountHook(sponsorID, sponsorCurrent, sponsorAdjustment);
+            }
+
+            auto sponsorshipSle = view.peek(keylet::sponsorship(sponsorID, accountID));
+            if (sponsorshipSle && adjustment > 0)
+            {
+                // Only decrease the pre-funded ReserveCount on Sponsorship if we assign new
+                // objects. Removing/reassigning ownership of the object doesn't increase
+                // RemainingOwnerCount back. Don't call hook because this counter is not something
+                // that requires reserve (like other sf...OwnerCounts do).
+                adjustOwnerCountImpl(
+                    view, sponsorshipSle, sfRemainingOwnerCount, sponsorID, -adjustment, j);
+            }
+        }
+
+        totalOwnerCount.owner =
+            adjustOwnerCountImpl(view, accountSle, sfOwnerCount, accountID, adjustment, j);
+        view.adjustOwnerCountHook(accountID, currentOwnerCount, totalOwnerCount);
+    }
+    else
+    {
+        XRPL_ASSERT(accountSle, "xrpl::adjustOwnerCountSigned : valid account sle");
+        if (!accountSle)
+            return;
+        // the remaining are only asserts to preserve existing behavior
+        XRPL_ASSERT(sponsorSle == nullptr, "xrpl::adjustOwnerCountSigned : sponsor not enabled");
+        XRPL_ASSERT(
+            accountSle->getType() == ltACCOUNT_ROOT,
+            "xrpl::adjustOwnerCountSigned : valid account sle type");
+        XRPL_ASSERT(adjustment, "xrpl::adjustOwnerCount : nonzero adjustment input");
+        std::uint32_t const current{accountSle->getFieldU32(sfOwnerCount)};
+        AccountID const id = (*accountSle)[sfAccount];
+        std::uint32_t const adjusted = confineOwnerCount(current, adjustment, id, j);
+
+        OwnerCounts const currentOwnerCount(accountSle);
+        OwnerCounts finalOwnerCount(currentOwnerCount);
+        finalOwnerCount.owner = adjusted;
+
+        view.adjustOwnerCountHook(id, currentOwnerCount, finalOwnerCount);
+        accountSle->at(sfOwnerCount) = adjusted;
+        view.update(accountSle);
+    }
+}
+
+}  // namespace
+
+std::uint32_t
+ownerCount(SLE::const_ref sle, beast::Journal j, std::int32_t ownerCountAdj)
+{
+    XRPL_ASSERT(sle && sle->getType() == ltACCOUNT_ROOT, "xrpl::ownerCount : sle is account root");
+
+    AccountID const id = sle->getAccountID(sfAccount);
+    std::uint32_t const currentOwnerCount = sle->at(sfOwnerCount);
+    std::uint32_t const sponsoredOwnerCount = sle->at(sfSponsoredOwnerCount);
+    std::uint32_t const sponsoringOwnerCount = sle->at(sfSponsoringOwnerCount);
+
+    XRPL_ASSERT(
+        currentOwnerCount >= sponsoredOwnerCount,
+        "xrpl::ownerCount : OwnerCount must be greater than or equal to SponsoredOwnerCount");
+
+    std::int64_t deltaCount =
+        static_cast<std::int64_t>(ownerCountAdj) - sponsoredOwnerCount + sponsoringOwnerCount;
+
+    if (deltaCount > std::numeric_limits<std::int32_t>::max())
+    {
+        // LCOV_EXCL_START
+        deltaCount = std::numeric_limits<std::int32_t>::max();
+        JLOG(j.fatal()) << "Account " << id << " delta count exceeds max, "
+                        << "adjustment: " << ownerCountAdj
+                        << ", sponsoredCount: " << sponsoredOwnerCount
+                        << ", sponsoringOwnerCount: " << sponsoringOwnerCount;
+        // LCOV_EXCL_STOP
+    }
+    else if (deltaCount < std::numeric_limits<std::int32_t>::min())
+    {
+        // LCOV_EXCL_START
+        deltaCount = std::numeric_limits<std::int32_t>::min();
+        JLOG(j.fatal()) << "Account " << id << " delta count is below min, "
+                        << "adjustment: " << ownerCountAdj
+                        << ", sponsoredCount: " << sponsoredOwnerCount
+                        << ", sponsoringCount: " << sponsoringOwnerCount;
+        // LCOV_EXCL_STOP
+    }
+
+    return confineOwnerCount(currentOwnerCount, deltaCount);
 }
 
 XRPAmount
@@ -91,12 +274,14 @@ xrpLiquid(ReadView const& view, AccountID const& id, std::int32_t ownerCountAdj,
         return beast::kZero;
 
     // Return balance minus reserve
-    std::uint32_t const ownerCount =
-        confineOwnerCount(view.ownerCountHook(id, sle->getFieldU32(sfOwnerCount)), ownerCountAdj);
+    std::uint32_t const currentOwnerCount =
+        confineOwnerCount(view.ownerCountHook(id, OwnerCounts(sle)).count(), ownerCountAdj);
+    std::uint32_t const currentAccountCount = accountCountImpl(sle, 0, j);
 
     // Pseudo-accounts have no reserve requirement
-    auto const reserve =
-        isPseudoAccount(sle) ? XRPAmount{0} : view.fees().accountReserve(ownerCount);
+    auto const reserve = isPseudoAccount(sle)
+        ? XRPAmount{0}
+        : view.fees().accountReserve(currentOwnerCount, currentAccountCount);
 
     auto const fullBalance = sle->getFieldAmount(sfBalance);
 
@@ -108,7 +293,7 @@ xrpLiquid(ReadView const& view, AccountID const& id, std::int32_t ownerCountAdj,
                     << " amount=" << amount.getFullText()
                     << " fullBalance=" << fullBalance.getFullText()
                     << " balance=" << balance.getFullText() << " reserve=" << reserve
-                    << " ownerCount=" << ownerCount << " ownerCountAdj=" << ownerCountAdj;
+                    << " ownerCount=" << currentOwnerCount << " ownerCountAdj=" << ownerCountAdj;
 
     return amount.xrp();
 }
@@ -125,19 +310,193 @@ transferRate(ReadView const& view, AccountID const& issuer)
 }
 
 void
-adjustOwnerCount(ApplyView& view, SLE::ref sle, std::int32_t amount, beast::Journal j)
+increaseOwnerCount(
+    ApplyView& view,
+    SLE::ref accountSle,
+    SLE::ref sponsorSle,
+    std::uint32_t count,
+    beast::Journal j)
 {
-    if (!sle)
-        return;
-    XRPL_ASSERT(amount, "xrpl::adjustOwnerCount : nonzero amount input");
-    std::uint32_t const current{sle->getFieldU32(sfOwnerCount)};
-    AccountID const id = (*sle)[sfAccount];
-    std::uint32_t const adjusted = confineOwnerCount(current, amount, id, j);
-    view.adjustOwnerCountHook(id, current, adjusted);
-    sle->at(sfOwnerCount) = adjusted;
-    view.update(sle);
+    XRPL_ASSERT(
+        count != 0 && count <= std::numeric_limits<std::int32_t>::max(),
+        "xrpl::increaseOwnerCount : count in signed delta range");
+    if (count == 0 || count > std::numeric_limits<std::int32_t>::max())
+        return;  // LCOV_EXCL_LINE
+
+    adjustOwnerCountSigned(view, accountSle, sponsorSle, static_cast<std::int32_t>(count), j);
 }
 
+void
+increaseOwnerCount(ApplyViewContext ctx, SLE::ref accountSle, std::uint32_t count, beast::Journal j)
+{
+    auto const sponsorExp = getEffectiveTxReserveSponsor(ctx, accountSle);
+
+    // The sponsor's existence is validated by checkReserve/checkSponsor before
+    // any owner-count mutation, so loading it here cannot fail.
+    XRPL_ASSERT(
+        sponsorExp.has_value(), "xrpl::increaseOwnerCount : sponsor validated before mutation");
+
+    increaseOwnerCount(ctx.view, accountSle, sponsorExp ? *sponsorExp : SLE::pointer(), count, j);
+}
+
+void
+decreaseOwnerCount(
+    ApplyView& view,
+    SLE::ref accountSle,
+    SLE::ref sponsorSle,
+    std::uint32_t count,
+    beast::Journal j)
+{
+    XRPL_ASSERT(
+        count != 0 && count <= std::numeric_limits<std::int32_t>::max(),
+        "xrpl::decreaseOwnerCount : count in signed delta range");
+    if (count == 0 || count > std::numeric_limits<std::int32_t>::max())
+        return;  // LCOV_EXCL_LINE
+
+    adjustOwnerCountSigned(view, accountSle, sponsorSle, -static_cast<std::int32_t>(count), j);
+}
+
+void
+decreaseOwnerCountForObject(
+    ApplyView& view,
+    SLE::ref accountSle,
+    SLE::ref objectSle,
+    std::uint32_t count,
+    beast::Journal j)
+{
+    XRPL_ASSERT(objectSle, "xrpl::decreaseOwnerCountForObject : valid object sle");
+    if (!objectSle)
+        return;  // LCOV_EXCL_LINE
+
+    bool const validObjectType = objectSle->getType() != ltACCOUNT_ROOT;
+    XRPL_ASSERT(validObjectType, "xrpl::decreaseOwnerCountForObject : valid object sle type");
+    if (!validObjectType)
+        return;  // LCOV_EXCL_LINE
+
+    SLE::ref sponsorSle = getLedgerEntryReserveSponsor(view, objectSle);
+    decreaseOwnerCount(view, accountSle, sponsorSle, count, j);
+}
+
+void
+adjustLoanBrokerOwnerCount(
+    ApplyView& view,
+    SLE::ref brokerSle,
+    std::int32_t delta,
+    beast::Journal j)
+{
+    XRPL_ASSERT(
+        brokerSle && brokerSle->getType() == ltLOAN_BROKER,
+        "xrpl::adjustLoanBrokerOwnerCount : valid loan broker sle");
+    if (!brokerSle || brokerSle->getType() != ltLOAN_BROKER)
+        return;  // LCOV_EXCL_LINE
+
+    XRPL_ASSERT(delta != 0, "xrpl::adjustLoanBrokerOwnerCount : nonzero delta input");
+    if (delta == 0)
+        return;  // LCOV_EXCL_LINE
+
+    adjustOwnerCountImpl(
+        view, brokerSle, sfOwnerCount, brokerSle->getAccountID(sfAccount), delta, j);
+}
+
+XRPAmount
+accountReserve(ReadView const& view, SLE::const_ref sle, beast::Journal j, Adjustment adj)
+{
+    XRPL_ASSERT(sle && sle->getType() == ltACCOUNT_ROOT, "xrpl::accountReserve : valid sle");
+
+    if (!view.rules().enabled(featureSponsor))
+    {
+        XRPL_ASSERT(adj.accountCountDelta == 0, "xrpl::accountReserve : no account count delta");
+        return view.fees().accountReserve(sle->getFieldU32(sfOwnerCount) + adj.ownerCountDelta, 1);
+    }
+    std::uint32_t const currentOwnerCount = ownerCount(sle, j, adj.ownerCountDelta);
+    std::uint32_t const currentAccountCount = accountCountImpl(sle, adj.accountCountDelta, j);
+
+    return view.fees().accountReserve(currentOwnerCount, currentAccountCount);
+}
+
+TER
+checkReserve(
+    ApplyViewContext ctx,
+    SLE::const_ref accSle,
+    XRPAmount accBalance,
+    SLE::const_ref sponsorSle,
+    Adjustment adj,
+    beast::Journal j,
+    TER insufReserveCode)
+{
+    // TODO: swap to assert after fixCleanup3_2_0 is retired
+    if (!accSle || accSle->getType() != ltACCOUNT_ROOT)
+        return tefINTERNAL;  // LCOV_EXCL_LINE
+    XRPL_ASSERT(
+        !isTesSuccess(insufReserveCode), "xrpl::checkReserve : insufReserveCode is not tesSUCCESS");
+    if (ctx.view.rules().enabled(featureSponsor))
+    {
+        if (sponsorSle)
+        {
+            if (sponsorSle->getType() != ltACCOUNT_ROOT)
+                return tefINTERNAL;  // LCOV_EXCL_LINE
+
+            auto const sle = ctx.view.read(
+                keylet::sponsorship(
+                    sponsorSle->getAccountID(sfAccount), accSle->getAccountID(sfAccount)));
+
+            // A reserve-sponsored tx must carry a sponsor signature
+            // (cosigning path) and/or have a pre-existing sponsorship SLE
+            // (prefunded path). Absence of both is an internal invariant break.
+            if (isReserveSponsored(ctx.tx) && !sle && !ctx.tx.isFieldPresent(sfSponsorSignature))
+                return tecINTERNAL;  // LCOV_EXCL_LINE
+
+            if (sle)
+            {
+                auto const ownerCountAllowed = sle->getFieldU32(sfRemainingOwnerCount);
+                if (adj.ownerCountDelta > 0 &&
+                    ownerCountAllowed < static_cast<std::uint32_t>(adj.ownerCountDelta))
+                    return insufReserveCode;
+            }
+
+            auto const sponsorBalance = sponsorSle->getFieldAmount(sfBalance).xrp();
+            XRPAmount const sponsorReserve = accountReserve(ctx.view, sponsorSle, j, adj);
+
+            if (sponsorBalance < sponsorReserve)
+                return insufReserveCode;
+        }
+        else
+        {
+            XRPAmount const reserve = accountReserve(ctx.view, accSle, j, adj);
+            if (accBalance < reserve)
+                return insufReserveCode;
+        }
+    }
+    else
+    {
+        XRPL_ASSERT(
+            !sponsorSle,
+            "xrpl::checkReserve : featureSponsor disabled and sponsorSle not provided");
+        XRPL_ASSERT(adj.accountCountDelta == 0, "xrpl::checkReserve : accountCountDelta is 0");
+        auto const reserve = ctx.view.fees().accountReserve(
+            accSle->getFieldU32(sfOwnerCount) + adj.ownerCountDelta, 1);
+        if (accBalance < reserve)
+            return insufReserveCode;
+    }
+    return tesSUCCESS;
+}
+
+TER
+checkReserve(
+    ApplyViewContext ctx,
+    SLE::const_ref accSle,
+    XRPAmount accBalance,
+    Adjustment adj,
+    beast::Journal j)
+{
+    auto const sponsorExp = getEffectiveTxReserveSponsor(ctx, accSle);
+    if (!sponsorExp)
+        return sponsorExp.error();  // LCOV_EXCL_LINE
+    return checkReserve(ctx, accSle, accBalance, *sponsorExp, adj, j);
+}
+
+// ----------------------------------------------------
+
 AccountID
 pseudoAccountAddress(ReadView const& view, uint256 const& pseudoOwnerKey)
 {

src/libxrpl/ledger/helpers/CredentialHelpers.cpp

@@ -97,7 +97,7 @@ deleteSLE(ApplyView& view, SLE::ref sleCredential, beast::Journal j)
         }
 
         if (isOwner)
-            adjustOwnerCount(view, sleAccount, -1, j);
+            decreaseOwnerCountForObject(view, sleAccount, sleCredential, 1, j);
 
         return tesSUCCESS;
     };

src/libxrpl/ledger/helpers/MPTokenHelpers.cpp

@@ -3,7 +3,6 @@
 #include <xrpl/basics/Log.h>
 #include <xrpl/basics/contract.h>
 #include <xrpl/beast/utility/Journal.h>
-#include <xrpl/beast/utility/Zero.h>
 #include <xrpl/beast/utility/instrumentation.h>
 #include <xrpl/ledger/ApplyView.h>
 #include <xrpl/ledger/ReadView.h>
@@ -11,6 +10,7 @@
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/CredentialHelpers.h>
 #include <xrpl/ledger/helpers/DirectoryHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/ledger/helpers/TokenHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Feature.h>
@@ -125,29 +125,29 @@ canAddHolding(ReadView const& view, MPTIssue const& mptIssue)
 
 [[nodiscard]] TER
 addEmptyHolding(
-    ApplyView& view,
+    ApplyViewContext ctx,
     AccountID const& accountID,
     XRPAmount priorBalance,
     MPTIssue const& mptIssue,
     beast::Journal journal)
 {
     auto const& mptID = mptIssue.getMptID();
-    auto const mpt = view.peek(keylet::mptokenIssuance(mptID));
+    auto const mpt = ctx.view.peek(keylet::mptokenIssuance(mptID));
     if (!mpt)
         return tefINTERNAL;  // LCOV_EXCL_LINE
     if (mpt->isFlag(lsfMPTLocked))
         return tefINTERNAL;  // LCOV_EXCL_LINE
-    if (view.peek(keylet::mptoken(mptID, accountID)))
+    if (ctx.view.peek(keylet::mptoken(mptID, accountID)))
         return tecDUPLICATE;
     if (accountID == mptIssue.getIssuer())
         return tesSUCCESS;
 
-    return authorizeMPToken(view, priorBalance, mptID, accountID, journal);
+    return authorizeMPToken(ctx, priorBalance, mptID, accountID, journal);
 }
 
 [[nodiscard]] TER
 authorizeMPToken(
-    ApplyView& view,
+    ApplyViewContext ctx,
     XRPAmount const& priorBalance,
     MPTID const& mptIssuanceID,
     AccountID const& account,
@@ -155,7 +155,7 @@ authorizeMPToken(
     std::uint32_t flags,
     std::optional<AccountID> holderID)
 {
-    auto const sleAcct = view.peek(keylet::account(account));
+    auto const sleAcct = ctx.view.peek(keylet::account(account));
     if (!sleAcct)
         return tecINTERNAL;  // LCOV_EXCL_LINE
 
@@ -170,19 +170,19 @@ authorizeMPToken(
         if ((flags & tfMPTUnauthorize) != 0u)
         {
             auto const mptokenKey = keylet::mptoken(mptIssuanceID, account);
-            auto const sleMpt = view.peek(mptokenKey);
+            auto const sleMpt = ctx.view.peek(mptokenKey);
             if (!sleMpt || (*sleMpt)[sfMPTAmount] != 0 ||
-                (view.rules().enabled(fixCleanup3_1_3) &&
+                (ctx.view.rules().enabled(fixCleanup3_1_3) &&
                  (*sleMpt)[~sfLockedAmount].valueOr(0) != 0))
                 return tecINTERNAL;  // LCOV_EXCL_LINE
 
-            if (!view.dirRemove(
+            if (!ctx.view.dirRemove(
                     keylet::ownerDir(account), (*sleMpt)[sfOwnerNode], sleMpt->key(), false))
                 return tecINTERNAL;  // LCOV_EXCL_LINE
 
-            adjustOwnerCount(view, sleAcct, -1, journal);
+            decreaseOwnerCountForObject(ctx.view, sleAcct, sleMpt, 1, journal);
 
-            view.erase(sleMpt);
+            ctx.view.erase(sleMpt);
             return tesSUCCESS;
         }
 
@@ -190,47 +190,57 @@ authorizeMPToken(
         //      - add the new mptokenKey to the owner directory
         //      - create the MPToken object for the holder
 
+        // A reserve sponsor only covers tx.Account's own objects.
+        auto const sponsorExp = getEffectiveTxReserveSponsor(ctx, sleAcct);
+        if (!sponsorExp)
+            return sponsorExp.error();  // LCOV_EXCL_LINE
+        auto const sponsorSle = *sponsorExp;
+
         // The reserve that is required to create the MPToken. Note
         // that although the reserve increases with every item
         // an account owns, in the case of MPTokens we only
         // *enforce* a reserve if the user owns more than two
         // items. This is similar to the reserve requirements of trust lines.
-        std::uint32_t const uOwnerCount = sleAcct->getFieldU32(sfOwnerCount);
-        XRPAmount const reserveCreate(
-            (uOwnerCount < 2) ? XRPAmount(beast::kZero)
-                              : view.fees().accountReserve(uOwnerCount + 1));
-
-        if (priorBalance < reserveCreate)
-            return tecINSUFFICIENT_RESERVE;
+        // The "free-tier" shortcut (ownerCount < 2) does not apply once a sponsor is on
+        // the tx — the sponsor must always cover the reserve (via balance or prefunded
+        // budget), so this check always runs for sponsored transactions.
+        if (sponsorSle || ownerCount(sleAcct, journal) >= 2)
+        {
+            if (auto const ret = checkReserve(
+                    ctx, sleAcct, priorBalance, sponsorSle, {.ownerCountDelta = 1}, journal);
+                !isTesSuccess(ret))
+                return ret;
+        }
 
         // Defensive check before we attempt to create MPToken for the issuer
-        auto const mpt = view.read(keylet::mptokenIssuance(mptIssuanceID));
+        auto const mpt = ctx.view.read(keylet::mptokenIssuance(mptIssuanceID));
         if (!mpt || mpt->getAccountID(sfIssuer) == account)
         {
             // LCOV_EXCL_START
             UNREACHABLE("xrpl::authorizeMPToken : invalid issuance or issuers token");
-            if (view.rules().enabled(featureLendingProtocol))
+            if (ctx.view.rules().enabled(featureLendingProtocol))
                 return tecINTERNAL;
             // LCOV_EXCL_STOP
         }
 
         auto const mptokenKey = keylet::mptoken(mptIssuanceID, account);
         auto mptoken = std::make_shared<SLE>(mptokenKey);
-        if (auto ter = dirLink(view, account, mptoken))
+        if (auto ter = dirLink(ctx.view, account, mptoken))
             return ter;  // LCOV_EXCL_LINE
 
         (*mptoken)[sfAccount] = account;
         (*mptoken)[sfMPTokenIssuanceID] = mptIssuanceID;
         (*mptoken)[sfFlags] = 0;
-        view.insert(mptoken);
+        ctx.view.insert(mptoken);
 
         // Update owner count.
-        adjustOwnerCount(view, sleAcct, 1, journal);
+        increaseOwnerCount(ctx.view, sleAcct, sponsorSle, 1, journal);
+        addSponsorToLedgerEntry(mptoken, sponsorSle);
 
         return tesSUCCESS;
     }
 
-    auto const sleMptIssuance = view.read(keylet::mptokenIssuance(mptIssuanceID));
+    auto const sleMptIssuance = ctx.view.read(keylet::mptokenIssuance(mptIssuanceID));
     if (!sleMptIssuance)
         return tecINTERNAL;  // LCOV_EXCL_LINE
 
@@ -240,7 +250,7 @@ authorizeMPToken(
     if (account != (*sleMptIssuance)[sfIssuer])
         return tecINTERNAL;  // LCOV_EXCL_LINE
 
-    auto const sleMpt = view.peek(keylet::mptoken(mptIssuanceID, *holderID));
+    auto const sleMpt = ctx.view.peek(keylet::mptoken(mptIssuanceID, *holderID));
     if (!sleMpt)
         return tecINTERNAL;  // LCOV_EXCL_LINE
 
@@ -263,13 +273,13 @@ authorizeMPToken(
     if (flagsIn != flagsOut)
         sleMpt->setFieldU32(sfFlags, flagsOut);
 
-    view.update(sleMpt);
+    ctx.view.update(sleMpt);
     return tesSUCCESS;
 }
 
 [[nodiscard]] TER
 removeEmptyHolding(
-    ApplyView& view,
+    ApplyViewContext ctx,
     AccountID const& accountID,
     MPTIssue const& mptIssue,
     beast::Journal journal)
@@ -279,7 +289,7 @@ removeEmptyHolding(
     // a token does exist, it will get deleted. If not, return success.
     bool const accountIsIssuer = accountID == mptIssue.getIssuer();
     auto const& mptID = mptIssue.getMptID();
-    auto const mptoken = view.peek(keylet::mptoken(mptID, accountID));
+    auto const mptoken = ctx.view.peek(keylet::mptoken(mptID, accountID));
     if (!mptoken)
         return accountIsIssuer ? (TER)tesSUCCESS : (TER)tecOBJECT_NOT_FOUND;
     // Unlike a trust line, if the account is the issuer, and the token has a
@@ -287,7 +297,7 @@ removeEmptyHolding(
     // accounting out of balance, so fail. Since this should be impossible
     // anyway, I'm not going to put any effort into it.
     if (mptoken->at(sfMPTAmount) != 0 ||
-        (view.rules().enabled(fixCleanup3_1_3) && (*mptoken)[~sfLockedAmount].valueOr(0) != 0))
+        (ctx.view.rules().enabled(fixCleanup3_1_3) && (*mptoken)[~sfLockedAmount].valueOr(0) != 0))
         return tecHAS_OBLIGATIONS;
 
     // Don't delete if the token still has confidential balances
@@ -300,7 +310,7 @@ removeEmptyHolding(
     }
 
     return authorizeMPToken(
-        view,
+        ctx,
         {},  // priorBalance
         mptID,
         accountID,
@@ -419,13 +429,13 @@ requireAuth(
 
 [[nodiscard]] TER
 enforceMPTokenAuthorization(
-    ApplyView& view,
+    ApplyViewContext ctx,
     MPTID const& mptIssuanceID,
     AccountID const& account,
     XRPAmount const& priorBalance,  // for MPToken authorization
     beast::Journal j)
 {
-    auto const sleIssuance = view.read(keylet::mptokenIssuance(mptIssuanceID));
+    auto const sleIssuance = ctx.view.read(keylet::mptokenIssuance(mptIssuanceID));
     if (!sleIssuance)
         return tefINTERNAL;  // LCOV_EXCL_LINE
 
@@ -437,7 +447,7 @@ enforceMPTokenAuthorization(
         return tefINTERNAL;  // LCOV_EXCL_LINE
 
     auto const keylet = keylet::mptoken(mptIssuanceID, account);
-    auto const sleToken = view.read(keylet);  //  NOTE: might be null
+    auto const sleToken = ctx.view.read(keylet);  //  NOTE: might be null
     auto const maybeDomainID = sleIssuance->at(~sfDomainID);
     bool expired = false;
     bool const authorizedByDomain = [&]() -> bool {
@@ -445,7 +455,7 @@ enforceMPTokenAuthorization(
         if (!maybeDomainID.has_value())
             return false;  // LCOV_EXCL_LINE
 
-        auto const ter = verifyValidDomain(view, account, *maybeDomainID, j);
+        auto const ter = verifyValidDomain(ctx.view, account, *maybeDomainID, j);
         if (isTesSuccess(ter))
             return true;
         if (ter == tecEXPIRED)
@@ -500,7 +510,7 @@ enforceMPTokenAuthorization(
             maybeDomainID.has_value() && sleToken == nullptr,
             "xrpl::enforceMPTokenAuthorization : new MPToken for domain");
         if (auto const err = authorizeMPToken(
-                view,
+                ctx,
                 priorBalance,   // priorBalance
                 mptIssuanceID,  // mptIssuanceID
                 account,        // account
@@ -915,6 +925,7 @@ createMPToken(
     ApplyView& view,
     MPTID const& mptIssuanceID,
     AccountID const& account,
+    SLE::ref sponsorSle,
     std::uint32_t const flags)
 {
     auto const mptokenKey = keylet::mptoken(mptIssuanceID, account);
@@ -931,6 +942,8 @@ createMPToken(
     (*mptoken)[sfFlags] = flags;
     (*mptoken)[sfOwnerNode] = *ownerNode;
 
+    addSponsorToLedgerEntry(mptoken, sponsorSle);
+
     view.insert(mptoken);
 
     return tesSUCCESS;
@@ -941,6 +954,7 @@ checkCreateMPT(
     xrpl::ApplyView& view,
     xrpl::MPTIssue const& mptIssue,
     xrpl::AccountID const& holder,
+    SLE::ref sponsorSle,
     beast::Journal j)
 {
     if (mptIssue.getIssuer() == holder)
@@ -950,7 +964,7 @@ checkCreateMPT(
     auto const mptokenID = keylet::mptoken(mptIssuanceID.key, holder);
     if (!view.exists(mptokenID))
     {
-        if (auto const err = createMPToken(view, mptIssue.getMptID(), holder, 0);
+        if (auto const err = createMPToken(view, mptIssue.getMptID(), holder, sponsorSle, 0);
             !isTesSuccess(err))
         {
             return err;
@@ -960,7 +974,8 @@ checkCreateMPT(
         {
             return tecINTERNAL;
         }
-        adjustOwnerCount(view, sleAcct, 1, j);
+
+        increaseOwnerCount(view, sleAcct, sponsorSle, 1, j);
     }
     return tesSUCCESS;
 }

src/libxrpl/ledger/helpers/NFTokenHelpers.cpp

@@ -269,11 +269,7 @@ insertToken(ApplyView& view, AccountID owner, STObject&& nft)
     // the NFT.
     SLE::pointer const page =
         getPageForToken(view, owner, nft[sfNFTokenID], [](ApplyView& view, AccountID const& owner) {
-            adjustOwnerCount(
-                view,
-                view.peek(keylet::account(owner)),
-                1,
-                beast::Journal{beast::Journal::getNullSink()});
+            increaseOwnerCount(view, owner, {}, 1, beast::Journal{beast::Journal::getNullSink()});
         });
 
     if (!page)
@@ -411,21 +407,17 @@ removeToken(ApplyView& view, AccountID const& owner, uint256 const& nftokenID, S
         curr->setFieldArray(sfNFTokens, arr);
         view.update(curr);
 
-        int cnt = 0;
+        std::uint32_t cnt = 0;
 
         if (prev && mergePages(view, prev, curr))
-            cnt--;
+            ++cnt;
 
         if (next && mergePages(view, curr, next))
-            cnt--;
+            ++cnt;
 
         if (cnt != 0)
         {
-            adjustOwnerCount(
-                view,
-                view.peek(keylet::account(owner)),
-                cnt,
-                beast::Journal{beast::Journal::getNullSink()});
+            decreaseOwnerCount(view, owner, {}, cnt, beast::Journal{beast::Journal::getNullSink()});
         }
 
         return tesSUCCESS;
@@ -460,11 +452,7 @@ removeToken(ApplyView& view, AccountID const& owner, uint256 const& nftokenID, S
                 curr->makeFieldAbsent(sfPreviousPageMin);
             }
 
-            adjustOwnerCount(
-                view,
-                view.peek(keylet::account(owner)),
-                -1,
-                beast::Journal{beast::Journal::getNullSink()});
+            decreaseOwnerCount(view, owner, {}, 1, beast::Journal{beast::Journal::getNullSink()});
 
             view.update(curr);
             view.erase(prev);
@@ -502,7 +490,7 @@ removeToken(ApplyView& view, AccountID const& owner, uint256 const& nftokenID, S
 
     view.erase(curr);
 
-    int cnt = 1;
+    uint32_t cnt = 1;
 
     // Since we're here, try to consolidate the previous and current pages
     // of the page we removed (if any) into one.  mergePages() _should_
@@ -519,11 +507,7 @@ removeToken(ApplyView& view, AccountID const& owner, uint256 const& nftokenID, S
             view.peek(Keylet(ltNFTOKEN_PAGE, next->key()))))
         cnt++;
 
-    adjustOwnerCount(
-        view,
-        view.peek(keylet::account(owner)),
-        -1 * cnt,
-        beast::Journal{beast::Journal::getNullSink()});
+    decreaseOwnerCount(view, owner, {}, cnt, beast::Journal{beast::Journal::getNullSink()});
 
     return tesSUCCESS;
 }
@@ -639,8 +623,7 @@ deleteTokenOffer(ApplyView& view, SLE::ref offer)
             false))
         return false;
 
-    adjustOwnerCount(
-        view, view.peek(keylet::account(owner)), -1, beast::Journal{beast::Journal::getNullSink()});
+    decreaseOwnerCount(view, owner, {}, 1, beast::Journal{beast::Journal::getNullSink()});
 
     view.erase(offer);
     return true;
@@ -743,9 +726,11 @@ repairNFTokenDirectoryLinks(ApplyView& view, AccountID const& owner)
             auto const newPrev = view.peek(Keylet(ltNFTOKEN_PAGE, *prevLink));
             if (!newPrev)
             {
+                // LCOV_EXCL_START
                 Throw<std::runtime_error>(
                     "NFTokenPage directory for " + to_string(owner) +
-                    " cannot be repaired.  Unexpected link problem.");
+                    " cannot be repaired. Unexpected link problem.");
+                // LCOV_EXCL_STOP
             }
             newPrev->at(sfNextPageMin) = nextPage->key();
             view.update(newPrev);
@@ -931,7 +916,7 @@ tokenOfferCreateApply(
 {
     Keylet const acctKeylet = keylet::account(acctID);
     if (auto const acct = view.read(acctKeylet);
-        priorBalance < view.fees().accountReserve((*acct)[sfOwnerCount] + 1))
+        priorBalance < accountReserve(view, acct, j, {.ownerCountDelta = 1}))
         return tecINSUFFICIENT_RESERVE;
 
     auto const offerID = keylet::nftokenOffer(acctID, seqProxy.value());
@@ -983,7 +968,7 @@ tokenOfferCreateApply(
     }
 
     // Update owner count.
-    adjustOwnerCount(view, view.peek(acctKeylet), 1, j);
+    increaseOwnerCount(view, acctID, {}, 1, j);
 
     return tesSUCCESS;
 }

src/libxrpl/ledger/helpers/OfferHelpers.cpp

@@ -55,7 +55,7 @@ offerDelete(ApplyView& view, SLE::ref sle, beast::Journal j)
         }
     }
 
-    adjustOwnerCount(view, view.peek(keylet::account(owner)), -1, j);
+    decreaseOwnerCountForObject(view, owner, sle, 1, j);
 
     view.erase(sle);
 

src/libxrpl/ledger/helpers/PaymentChannelHelpers.cpp

@@ -58,7 +58,7 @@ closeChannel(SLE::ref slep, ApplyView& view, uint256 const& key, beast::Journal
     XRPL_ASSERT(
         (*slep)[sfAmount] >= (*slep)[sfBalance], "xrpl::closeChannel : minimum channel amount");
     (*sle)[sfBalance] = (*sle)[sfBalance] + (*slep)[sfAmount] - (*slep)[sfBalance];
-    adjustOwnerCount(view, sle, -1, j);
+    decreaseOwnerCountForObject(view, sle, slep, 1, j);
     view.update(sle);
 
     // Remove PayChan from ledger

src/libxrpl/ledger/helpers/RippleStateHelpers.cpp

@@ -9,6 +9,7 @@
 #include <xrpl/ledger/ReadView.h>
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/DirectoryHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/ledger/helpers/TokenHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/AmountConversions.h>
@@ -195,6 +196,7 @@ trustCreate(
                                 // Issuer should be the account being set.
     std::uint32_t uQualityIn,
     std::uint32_t uQualityOut,
+    SLE::ref sponsorSle,
     beast::Journal j)
 {
     JLOG(j.trace()) << "trustCreate: " << to_string(uSrcAccountID) << ", "
@@ -281,7 +283,9 @@ trustCreate(
     }
 
     sleRippleState->setFieldU32(sfFlags, uFlags);
-    adjustOwnerCount(view, sleAccount, 1, j);
+    increaseOwnerCount(view, sleAccount, sponsorSle, 1, j);
+
+    addSponsorToLedgerEntry(sleRippleState, sponsorSle, bSetHigh ? sfHighSponsor : sfLowSponsor);
 
     // ONLY: Create ripple balance.
     sleRippleState->setFieldAmount(sfBalance, bSetHigh ? -saBalance : saBalance);
@@ -317,6 +321,9 @@ trustDelete(
         return tefBAD_LEDGER;  // LCOV_EXCL_LINE
     }
 
+    removeSponsorFromLedgerEntry(sleRippleState, sfHighSponsor);
+    removeSponsorFromLedgerEntry(sleRippleState, sfLowSponsor);
+
     JLOG(j.trace()) << "trustDelete: Deleting ripple line: state";
     view.erase(sleRippleState);
 
@@ -369,11 +376,15 @@ updateTrustLine(
     {
         // VFALCO Where is the line being deleted?
         // Clear the reserve of the sender, possibly delete the line!
-        adjustOwnerCount(view, sle, -1, j);
+        auto const currentSponsor =
+            getLedgerEntryReserveSponsor(view, state, bSenderHigh ? sfHighSponsor : sfLowSponsor);
+        decreaseOwnerCount(view, sle, currentSponsor, 1, j);
 
         // Clear reserve flag.
         state->clearFlag(senderReserveFlag);
 
+        removeSponsorFromLedgerEntry(state, !bSenderHigh ? sfLowSponsor : sfHighSponsor);
+
         // Balance is zero, receiver reserve is clear.
         if (!after && !state->isFlag(receiverReserveFlag))
             return true;
@@ -381,12 +392,14 @@ updateTrustLine(
     return false;
 }
 
+// Only used in tests
 TER
 issueIOU(
     ApplyView& view,
     AccountID const& account,
     STAmount const& amount,
     Issue const& issue,
+    SLE::ref sponsorSle,
     beast::Journal j)
 {
     XRPL_ASSERT(
@@ -472,6 +485,7 @@ issueIOU(
         limit,
         0,
         0,
+        sponsorSle,
         j);
 }
 
@@ -620,7 +634,7 @@ canTransfer(ReadView const& view, Issue const& issue, AccountID const& from, Acc
 
 TER
 addEmptyHolding(
-    ApplyView& view,
+    ApplyViewContext ctx,
     AccountID const& accountID,
     XRPAmount priorBalance,
     Issue const& issue,
@@ -632,30 +646,45 @@ addEmptyHolding(
 
     auto const& issuerId = issue.getIssuer();
     auto const& currency = issue.currency;
-    if (isGlobalFrozen(view, issuerId))
+    if (isGlobalFrozen(ctx.view, issuerId))
         return tecFROZEN;  // LCOV_EXCL_LINE
 
     auto const& srcId = issuerId;
     auto const& dstId = accountID;
     auto const high = srcId > dstId;
     auto const index = keylet::trustLine(srcId, dstId, currency);
-    auto const sleSrc = view.peek(keylet::account(srcId));
-    auto const sleDst = view.peek(keylet::account(dstId));
+    auto const sleSrc = ctx.view.peek(keylet::account(srcId));
+    auto const sleDst = ctx.view.peek(keylet::account(dstId));
     if (!sleDst || !sleSrc)
         return tefINTERNAL;  // LCOV_EXCL_LINE
     if (!sleSrc->isFlag(lsfDefaultRipple))
         return tecINTERNAL;  // LCOV_EXCL_LINE
     // If the line already exists, don't create it again.
-    if (view.read(index))
+    if (ctx.view.read(index))
         return tecDUPLICATE;
 
+    // A reserve sponsor only covers tx.Account's own objects.
+    auto const sponsorExp = getEffectiveTxReserveSponsor(ctx, sleDst);
+    if (!sponsorExp)
+        return sponsorExp.error();  // LCOV_EXCL_LINE
+    auto const sponsorSle = *sponsorExp;
+
     // Can the account cover the trust line reserve ?
-    std::uint32_t const ownerCount = sleDst->at(sfOwnerCount);
-    if (priorBalance < view.fees().accountReserve(ownerCount + 1))
-        return tecNO_LINE_INSUF_RESERVE;
+    if (auto const ret = checkReserve(
+            ctx,
+            sleDst,
+            priorBalance,
+            sponsorSle,
+            {.ownerCountDelta = 1},
+            journal,
+            tecNO_LINE_INSUF_RESERVE);
+        !isTesSuccess(ret))
+    {
+        return ret;
+    }
 
     return trustCreate(
-        view,
+        ctx.view,
         high,
         srcId,
         dstId,
@@ -669,19 +698,20 @@ addEmptyHolding(
         /*saLimit=*/STAmount{Issue{currency, dstId}},
         /*uQualityIn=*/0,
         /*uQualityOut=*/0,
+        sponsorSle,
         journal);
 }
 
 TER
 removeEmptyHolding(
-    ApplyView& view,
+    ApplyViewContext ctx,
     AccountID const& accountID,
     Issue const& issue,
     beast::Journal journal)
 {
     if (issue.native())
     {
-        auto const sle = view.read(keylet::account(accountID));
+        auto const sle = ctx.view.read(keylet::account(accountID));
         if (!sle)
             return tecINTERNAL;  // LCOV_EXCL_LINE
 
@@ -696,7 +726,7 @@ removeEmptyHolding(
     // If the account is the issuer, then no line should exist. Check anyway.
     // If a line does exist, it will get deleted. If not, return success.
     bool const accountIsIssuer = accountID == issue.account;
-    auto const line = view.peek(keylet::trustLine(accountID, issue));
+    auto const line = ctx.view.peek(keylet::trustLine(accountID, issue));
     if (!line)
         return accountIsIssuer ? (TER)tesSUCCESS : (TER)tecOBJECT_NOT_FOUND;
     if (!accountIsIssuer && line->at(sfBalance)->iou() != beast::kZero)
@@ -706,33 +736,43 @@ removeEmptyHolding(
     if (line->isFlag(lsfLowReserve))
     {
         // Clear reserve for low account.
-        auto sleLowAccount = view.peek(keylet::account(line->at(sfLowLimit)->getIssuer()));
+        auto sleLowAccount = ctx.view.peek(keylet::account(line->at(sfLowLimit)->getIssuer()));
         if (!sleLowAccount)
             return tecINTERNAL;  // LCOV_EXCL_LINE
 
-        adjustOwnerCount(view, sleLowAccount, -1, journal);
+        auto const currentLowSponsor = getLedgerEntryReserveSponsor(ctx.view, line, sfLowSponsor);
+
+        decreaseOwnerCount(ctx.view, sleLowAccount, currentLowSponsor, 1, journal);
         // It's not really necessary to clear the reserve flag, since the line
         // is about to be deleted, but this will make the metadata reflect an
         // accurate state at the time of deletion.
         line->clearFlag(lsfLowReserve);
+        removeSponsorFromLedgerEntry(line, sfLowSponsor);
     }
 
     if (line->isFlag(lsfHighReserve))
     {
         // Clear reserve for high account.
-        auto sleHighAccount = view.peek(keylet::account(line->at(sfHighLimit)->getIssuer()));
+        auto sleHighAccount = ctx.view.peek(keylet::account(line->at(sfHighLimit)->getIssuer()));
         if (!sleHighAccount)
             return tecINTERNAL;  // LCOV_EXCL_LINE
 
-        adjustOwnerCount(view, sleHighAccount, -1, journal);
+        auto const currentHighSponsor = getLedgerEntryReserveSponsor(ctx.view, line, sfHighSponsor);
+
+        decreaseOwnerCount(ctx.view, sleHighAccount, currentHighSponsor, 1, journal);
         // It's not really necessary to clear the reserve flag, since the line
         // is about to be deleted, but this will make the metadata reflect an
         // accurate state at the time of deletion.
         line->clearFlag(lsfHighReserve);
+        removeSponsorFromLedgerEntry(line, sfHighSponsor);
     }
 
     return trustDelete(
-        view, line, line->at(sfLowLimit)->getIssuer(), line->at(sfHighLimit)->getIssuer(), journal);
+        ctx.view,
+        line,
+        line->at(sfLowLimit)->getIssuer(),
+        line->at(sfHighLimit)->getIssuer(),
+        journal);
 }
 
 TER
@@ -768,6 +808,9 @@ deleteAMMTrustLine(
     if (ammAccountID && (low != *ammAccountID && high != *ammAccountID))
         return terNO_AMM;
 
+    auto const sponsorSle =
+        getLedgerEntryReserveSponsor(view, sleState, !ammLow ? sfLowSponsor : sfHighSponsor);
+
     if (auto const ter = trustDelete(view, sleState, low, high, j); !isTesSuccess(ter))
     {
         JLOG(j.error()) << "deleteAMMTrustLine: failed to delete the trustline.";
@@ -778,7 +821,7 @@ deleteAMMTrustLine(
     if (!sleState->isFlag(uFlags))
         return tecINTERNAL;  // LCOV_EXCL_LINE
 
-    adjustOwnerCount(view, !ammLow ? sleLow : sleHigh, -1, j);
+    decreaseOwnerCount(view, !ammLow ? sleLow : sleHigh, sponsorSle, 1, j);
 
     return tesSUCCESS;
 }

src/libxrpl/ledger/helpers/SponsorHelpers.cpp

@@ -0,0 +1,345 @@
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
+
+#include <xrpl/beast/utility/instrumentation.h>
+#include <xrpl/ledger/ApplyView.h>
+#include <xrpl/ledger/ReadView.h>
+#include <xrpl/ledger/helpers/AccountRootHelpers.h>
+#include <xrpl/ledger/helpers/OracleHelpers.h>
+#include <xrpl/protocol/AccountID.h>
+#include <xrpl/protocol/Feature.h>
+#include <xrpl/protocol/Indexes.h>
+#include <xrpl/protocol/LedgerFormats.h>
+#include <xrpl/protocol/Rules.h>
+#include <xrpl/protocol/SField.h>
+#include <xrpl/protocol/STArray.h>
+#include <xrpl/protocol/STLedgerEntry.h>
+#include <xrpl/protocol/STTx.h>
+#include <xrpl/protocol/TER.h>
+#include <xrpl/protocol/TxFormats.h>
+
+#include <cstdint>
+#include <expected>
+#include <optional>
+#include <unordered_set>
+
+namespace xrpl {
+
+bool
+isReserveSponsorAllowed(TxType txType)
+{
+    // Transaction types explicitly allow-listed for reserve sponsorship, for
+    // v1. Lazily-initialized function-local static: constructed once on first
+    // use, with no startup cost paid by clients that never call this.
+    static std::unordered_set<TxType> const kReserveSponsorAllowed = {
+        ttDELEGATE_SET,
+        ttDEPOSIT_PREAUTH,
+        ttPAYMENT,
+        ttSIGNER_LIST_SET,
+        ttCHECK_CANCEL,
+        ttCHECK_CASH,
+        ttCHECK_CREATE,
+        ttESCROW_CANCEL,
+        ttESCROW_CREATE,
+        ttESCROW_FINISH,
+        ttPAYCHAN_CLAIM,
+        ttPAYCHAN_CREATE,
+        ttPAYCHAN_FUND,
+        ttCLAWBACK,
+        ttMPTOKEN_AUTHORIZE,
+        ttMPTOKEN_ISSUANCE_CREATE,
+        ttMPTOKEN_ISSUANCE_DESTROY,
+        ttMPTOKEN_ISSUANCE_SET,
+        ttTRUST_SET,
+        ttCREDENTIAL_ACCEPT,
+        ttCREDENTIAL_CREATE,
+        ttCREDENTIAL_DELETE,
+        ttACCOUNT_SET,
+        ttREGULAR_KEY_SET,
+        ttSPONSORSHIP_TRANSFER,
+    };
+    return kReserveSponsorAllowed.contains(txType);
+}
+
+std::optional<AccountID>
+getTxReserveSponsorID(STTx const& tx)
+{
+    if (tx.isFieldPresent(sfSponsor) && isReserveSponsored(tx))
+    {
+        XRPL_ASSERT(
+            getCurrentTransactionRules()->enabled(  // NOLINT(bugprone-unchecked-optional-access)
+                featureSponsor),
+            "xrpl::getTxReserveSponsorID : sponsor exists + Sponsor enabled");
+        return tx.getAccountID(sfSponsor);
+    }
+    return {};
+}
+
+std::expected<SLE::pointer, TER>
+getTxReserveSponsor(ApplyViewContext ctx)
+{
+    auto const sponsorID = getTxReserveSponsorID(ctx.tx);
+    if (sponsorID)
+    {
+        XRPL_ASSERT(
+            ctx.view.rules().enabled(featureSponsor),
+            "xrpl::getTxReserveSponsor : sponsor exists + Sponsor enabled");
+        auto sle = ctx.view.peek(keylet::account(*sponsorID));
+
+        // already checked in Transactor::checkSponsor
+        if (!sle)
+            return std::unexpected(tecINTERNAL);  // LCOV_EXCL_LINE
+        return sle;
+    }
+    return SLE::pointer();
+}
+
+std::expected<SLE::const_pointer, TER>
+getTxReserveSponsor(ReadView const& view, STTx const& tx)
+{
+    auto const sponsorID = getTxReserveSponsorID(tx);
+    if (sponsorID)
+    {
+        XRPL_ASSERT(
+            view.rules().enabled(featureSponsor),
+            "xrpl::getTxReserveSponsor : sponsor exists + Sponsor enabled");
+        auto sle = view.read(keylet::account(*sponsorID));
+
+        // already checked in Transactor::checkSponsor
+        if (!sle)
+            return std::unexpected(tecINTERNAL);  // LCOV_EXCL_LINE
+        return sle;
+    }
+    return SLE::pointer();
+}
+
+std::expected<SLE::pointer, TER>
+getEffectiveTxReserveSponsor(ApplyViewContext ctx, SLE::const_ref accountSle)
+{
+    // A reserve sponsor only covers tx.Account's own objects.
+    if (ctx.view.rules().enabled(fixCleanup3_2_0))
+    {
+        XRPL_ASSERT(
+            accountSle && accountSle->getType() == ltACCOUNT_ROOT,
+            "xrpl::getEffectiveTxReserveSponsor : accountSle exists and is account type");
+    }
+    else
+    {
+        XRPL_ASSERT(
+            accountSle &&
+                ((accountSle->getType() == ltACCOUNT_ROOT) || (accountSle->getType() == ltESCROW)),
+            "xrpl::getEffectiveTxReserveSponsor : accountSle exists and is account type");
+    }
+
+    if (isPseudoAccount(accountSle) || accountSle->getAccountID(sfAccount) != ctx.tx[sfAccount])
+        return SLE::pointer();
+    return getTxReserveSponsor(ctx);
+}
+
+std::optional<AccountID>
+getLedgerEntryReserveSponsorID(SLE::const_ref sle, SF_ACCOUNT const& field)
+{
+    XRPL_ASSERT(
+        (sle &&
+         ((sle->getType() == ltRIPPLE_STATE && (field == sfHighSponsor || field == sfLowSponsor)) ||
+          (sle->getType() != ltRIPPLE_STATE && field == sfSponsor))),
+        "xrpl::getLedgerEntryReserveSponsorID : correct sfield");
+
+    if (sle->isFieldPresent(field))
+        return sle->getAccountID(field);
+    return {};
+}
+
+SLE::pointer
+getLedgerEntryReserveSponsor(ApplyView& view, SLE::const_ref sle, SF_ACCOUNT const& field)
+{
+    auto const sponsorID = getLedgerEntryReserveSponsorID(sle, field);
+    if (sponsorID)
+    {
+        XRPL_ASSERT(
+            view.rules().enabled(featureSponsor),
+            "xrpl::getLedgerEntryReserveSponsor : sponsor exists + Sponsor enabled");
+        return view.peek(keylet::account(*sponsorID));
+    }
+    return {};
+}
+
+void
+addSponsorToLedgerEntry(SLE::ref sle, SLE::const_ref sponsorSle, SF_ACCOUNT const& field)
+{
+    XRPL_ASSERT(
+        (sle->getType() == ltRIPPLE_STATE && (field == sfHighSponsor || field == sfLowSponsor)) ||
+            (sle->getType() != ltRIPPLE_STATE && field == sfSponsor),
+        "addSponsorToLedgerEntry : Invalid field to the LedgerEntry");
+    if (sponsorSle)
+    {
+        XRPL_ASSERT(
+            getCurrentTransactionRules()->enabled(  // NOLINT(bugprone-unchecked-optional-access)
+                featureSponsor),
+            "xrpl::addSponsorToLedgerEntry : sponsor exists + Sponsor enabled");
+        sle->setAccountID(field, sponsorSle->getAccountID(sfAccount));
+    }
+}
+
+void
+addSponsorToLedgerEntry(ApplyViewContext ctx, SLE::ref sle, SF_ACCOUNT const& field)
+{
+    // getTxReserveSponsor yields a null pointer when the tx is not
+    // reserve-sponsored, so addSponsorToLedgerEntry becomes a no-op then. The
+    // error case (tecINTERNAL) is an already-checked invariant; skip stamping.
+    auto const sponsorSle = getTxReserveSponsor(ctx);
+    if (sponsorSle && *sponsorSle)
+    {
+        XRPL_ASSERT(
+            ctx.view.rules().enabled(featureSponsor),
+            "xrpl::addSponsorToLedgerEntry : sponsor exists + Sponsor enabled");
+        addSponsorToLedgerEntry(sle, *sponsorSle, field);
+    }
+}
+
+void
+removeSponsorFromLedgerEntry(SLE::ref sle, SF_ACCOUNT const& field)
+{
+    XRPL_ASSERT(
+        (sle->getType() == ltRIPPLE_STATE && (field == sfHighSponsor || field == sfLowSponsor)) ||
+            (sle->getType() != ltRIPPLE_STATE && field == sfSponsor),
+        "removeSponsorFromLedgerEntry : Invalid field to the LedgerEntry");
+    if (sle->isFieldPresent(field))
+    {
+        XRPL_ASSERT(
+            getCurrentTransactionRules()->enabled(  // NOLINT(bugprone-unchecked-optional-access)
+                featureSponsor),
+            "xrpl::removeSponsorFromLedgerEntry : sponsor exists + Sponsor enabled");
+        sle->makeFieldAbsent(field);
+    }
+}
+
+bool
+isLedgerEntryOwner(ReadView const& view, SLE const& sle, AccountID const& account)
+{
+    switch (sle.getType())
+    {
+        case ltCHECK:
+        case ltESCROW:
+        case ltPAYCHAN:
+        case ltMPTOKEN:
+        case ltDELEGATE:
+        case ltDEPOSIT_PREAUTH:
+            return sle.getAccountID(sfAccount) == account;
+        case ltMPTOKEN_ISSUANCE:
+            return sle.getAccountID(sfIssuer) == account;
+        case ltSIGNER_LIST: {
+            auto const signerList = view.read(keylet::signerList(account));
+            if (!signerList)
+                return false;
+            return signerList->key() == sle.key();
+        }
+        case ltCREDENTIAL: {
+            auto const& ownerField = sle.isFlag(lsfAccepted) ? sfSubject : sfIssuer;
+            return sle.getAccountID(ownerField) == account;
+        }
+        case ltRIPPLE_STATE: {
+            if (sle.isFlag(lsfHighReserve))
+            {
+                auto const highAccount = sle.getFieldAmount(sfHighLimit).getIssuer();
+                if (highAccount == account)
+                    return true;
+            }
+            if (sle.isFlag(lsfLowReserve))
+            {
+                auto const lowAccount = sle.getFieldAmount(sfLowLimit).getIssuer();
+                if (lowAccount == account)
+                    return true;
+            }
+            // Reachable: the sponsee may be a third party or the side of the
+            // line that holds no reserve (e.g. the issuer). Callers map this
+            // to tecNO_PERMISSION.
+            return false;
+        }
+        default:
+            // LCOV_EXCL_START
+            UNREACHABLE("xrpl::isLedgerEntryOwner : object is not supported by sponsorship.");
+            return false;
+            // LCOV_EXCL_STOP
+    };
+}
+
+bool
+isLedgerEntrySupportedBySponsorship(SLE const& sle)
+{
+    switch (sle.getType())
+    {
+        case ltCHECK:
+        case ltESCROW:
+        case ltPAYCHAN:
+        case ltMPTOKEN:
+        case ltDELEGATE:
+        case ltDEPOSIT_PREAUTH:
+        case ltMPTOKEN_ISSUANCE:
+        case ltSIGNER_LIST:
+        case ltCREDENTIAL:
+        case ltRIPPLE_STATE:
+            return true;
+        default:
+            return false;
+    };
+}
+
+std::uint32_t
+getLedgerEntryOwnerCount(SLE const& sle)
+{
+    switch (sle.getType())
+    {
+        case ltORACLE: {
+            return calculateOracleReserve(sle.getFieldArray(sfPriceDataSeries));
+        }
+        // Vaults require 2 owner counts (the vault and a pseudo-account)
+        case ltVAULT:
+            return 2;
+        case ltSIGNER_LIST: {
+            // Mirror SignerListSet's owner-count accounting so that create and
+            // delete agree. Modern lists (post-MultiSignReserve) carry the
+            // lsfOneOwnerCount flag and cost a single owner count. Legacy
+            // pre-MultiSignReserve lists cost 2 + signer_count owner counts
+            if (sle.isFlag(lsfOneOwnerCount))
+                return 1;
+            return 2 + static_cast<std::uint32_t>(sle.getFieldArray(sfSignerEntries).size());
+        }
+        case ltACCOUNT_ROOT:
+            // LCOV_EXCL_START
+            UNREACHABLE("AccountRoots are not supported by object sponsorship.");
+            return 0;
+            // LCOV_EXCL_STOP
+        default:
+            return 1;
+    }
+}
+
+SF_ACCOUNT const&
+getLedgerEntrySponsorField(SLE const& sle, AccountID const& owner)
+{
+    switch (sle.getType())
+    {
+        case ltRIPPLE_STATE: {
+            if (sle.isFlag(lsfHighReserve))
+            {
+                auto const highAccount = sle.getFieldAmount(sfHighLimit).getIssuer();
+                if (highAccount == owner)
+                    return sfHighSponsor;
+            }
+            if (sle.isFlag(lsfLowReserve))
+            {
+                auto const lowAccount = sle.getFieldAmount(sfLowLimit).getIssuer();
+                if (lowAccount == owner)
+                    return sfLowSponsor;
+            }
+            // LCOV_EXCL_START
+            UNREACHABLE("xrpl::getLedgerEntrySponsorField : unknown owner for RippleState");
+            return sfSponsor;
+            // LCOV_EXCL_STOP
+        }
+        default:
+            return sfSponsor;
+    }
+}
+
+}  // namespace xrpl

src/libxrpl/ledger/helpers/TokenHelpers.cpp

@@ -10,6 +10,7 @@
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/MPTokenHelpers.h>
 #include <xrpl/ledger/helpers/RippleStateHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Asset.h>
 #include <xrpl/protocol/Concepts.h>
@@ -571,7 +572,7 @@ canAddHolding(ReadView const& view, Asset const& asset)
 
 TER
 addEmptyHolding(
-    ApplyView& view,
+    ApplyViewContext ctx,
     AccountID const& accountID,
     XRPAmount priorBalance,
     Asset const& asset,
@@ -579,21 +580,21 @@ addEmptyHolding(
 {
     return std::visit(
         [&]<ValidIssueType TIss>(TIss const& issue) -> TER {
-            return addEmptyHolding(view, accountID, priorBalance, issue, journal);
+            return addEmptyHolding(ctx, accountID, priorBalance, issue, journal);
         },
         asset.value());
 }
 
 TER
 removeEmptyHolding(
-    ApplyView& view,
+    ApplyViewContext ctx,
     AccountID const& accountID,
     Asset const& asset,
     beast::Journal journal)
 {
     return std::visit(
         [&]<ValidIssueType TIss>(TIss const& issue) -> TER {
-            return removeEmptyHolding(view, accountID, issue, journal);
+            return removeEmptyHolding(ctx, accountID, issue, journal);
         },
         asset.value());
 }
@@ -647,6 +648,7 @@ directSendNoFeeIOU(
     AccountID const& uReceiverID,
     STAmount const& saAmount,
     bool bCheckIssuer,
+    SLE::ref sponsorSle,
     beast::Journal j)
 {
     AccountID const& issuer = saAmount.getIssuer();
@@ -717,7 +719,12 @@ directSendNoFeeIOU(
         // Sender quality out is 0.
         {
             // Clear the reserve of the sender, possibly delete the line!
-            adjustOwnerCount(view, view.peek(keylet::account(uSenderID)), -1, j);
+            auto const currentSponsor = getLedgerEntryReserveSponsor(
+                view, sleRippleState, !bSenderHigh ? sfLowSponsor : sfHighSponsor);
+            decreaseOwnerCount(view, view.peek(keylet::account(uSenderID)), currentSponsor, 1, j);
+
+            removeSponsorFromLedgerEntry(
+                sleRippleState, !bSenderHigh ? sfLowSponsor : sfHighSponsor);
 
             // Clear reserve flag.
             sleRippleState->clearFlag(senderReserveFlag);
@@ -780,6 +787,7 @@ directSendNoFeeIOU(
         saReceiverLimit,
         0,
         0,
+        sponsorSle,
         j);
 }
 
@@ -794,6 +802,7 @@ directSendNoLimitIOU(
     STAmount const& saAmount,
     STAmount& saActual,
     beast::Journal j,
+    SLE::ref sponsorSle,
     WaiveTransferFee waiveFee)
 {
     auto const& issuer = saAmount.getIssuer();
@@ -806,7 +815,8 @@ directSendNoLimitIOU(
     if (uSenderID == issuer || uReceiverID == issuer || issuer == noAccount())
     {
         // Direct send: redeeming IOUs and/or sending own IOUs.
-        auto const ter = directSendNoFeeIOU(view, uSenderID, uReceiverID, saAmount, false, j);
+        auto const ter =
+            directSendNoFeeIOU(view, uSenderID, uReceiverID, saAmount, false, sponsorSle, j);
         if (!isTesSuccess(ter))
             return ter;
         saActual = saAmount;
@@ -824,10 +834,12 @@ directSendNoLimitIOU(
                     << to_string(uReceiverID) << " : deliver=" << saAmount.getFullText()
                     << " cost=" << saActual.getFullText();
 
-    TER terResult = directSendNoFeeIOU(view, issuer, uReceiverID, saAmount, true, j);
+    TER terResult = directSendNoFeeIOU(view, issuer, uReceiverID, saAmount, true, sponsorSle, j);
 
     if (tesSUCCESS == terResult)
-        terResult = directSendNoFeeIOU(view, uSenderID, issuer, saActual, true, j);
+    {
+        terResult = directSendNoFeeIOU(view, uSenderID, issuer, saActual, true, sponsorSle, j);
+    }
 
     return terResult;
 }
@@ -870,7 +882,8 @@ directSendNoLimitMultiIOU(
         if (senderID == issuer || receiverID == issuer || issuer == noAccount())
         {
             // Direct send: redeeming IOUs and/or sending own IOUs.
-            if (auto const ter = directSendNoFeeIOU(view, senderID, receiverID, amount, false, j);
+            if (auto const ter =
+                    directSendNoFeeIOU(view, senderID, receiverID, amount, false, {}, j);
                 !isTesSuccess(ter))
                 return ter;
             actual += amount;
@@ -894,14 +907,14 @@ directSendNoLimitMultiIOU(
                         << to_string(receiverID) << " : deliver=" << amount.getFullText()
                         << " cost=" << actual.getFullText();
 
-        if (TER const terResult = directSendNoFeeIOU(view, issuer, receiverID, amount, true, j))
+        if (TER const terResult = directSendNoFeeIOU(view, issuer, receiverID, amount, true, {}, j))
             return terResult;
     }
 
     if (senderID != issuer && takeFromSender)
     {
         if (TER const terResult =
-                directSendNoFeeIOU(view, senderID, issuer, takeFromSender, true, j))
+                directSendNoFeeIOU(view, senderID, issuer, takeFromSender, true, {}, j))
             return terResult;
     }
 
@@ -915,6 +928,7 @@ accountSendIOU(
     AccountID const& uReceiverID,
     STAmount const& saAmount,
     beast::Journal j,
+    SLE::ref sponsorSle,
     WaiveTransferFee waiveFee)
 {
     if (view.rules().enabled(fixAMMv1_1))
@@ -946,7 +960,8 @@ accountSendIOU(
         JLOG(j.trace()) << "accountSendIOU: " << to_string(uSenderID) << " -> "
                         << to_string(uReceiverID) << " : " << saAmount.getFullText();
 
-        return directSendNoLimitIOU(view, uSenderID, uReceiverID, saAmount, saActual, j, waiveFee);
+        return directSendNoLimitIOU(
+            view, uSenderID, uReceiverID, saAmount, saActual, j, sponsorSle, waiveFee);
     }
 
     /* XRP send which does not check reserve and can do pure adjustment.
@@ -1475,7 +1490,7 @@ directSendNoFee(
 {
     return saAmount.asset().visit(
         [&](Issue const&) {
-            return directSendNoFeeIOU(view, uSenderID, uReceiverID, saAmount, bCheckIssuer, j);
+            return directSendNoFeeIOU(view, uSenderID, uReceiverID, saAmount, bCheckIssuer, {}, j);
         },
         [&](MPTIssue const&) {
             XRPL_ASSERT(!bCheckIssuer, "xrpl::directSendNoFee : not checking issuer");
@@ -1490,12 +1505,13 @@ accountSend(
     AccountID const& uReceiverID,
     STAmount const& saAmount,
     beast::Journal j,
+    SLE::ref sponsorSle,
     WaiveTransferFee waiveFee,
     AllowMPTOverflow allowOverflow)
 {
     return saAmount.asset().visit(
         [&](Issue const&) {
-            return accountSendIOU(view, uSenderID, uReceiverID, saAmount, j, waiveFee);
+            return accountSendIOU(view, uSenderID, uReceiverID, saAmount, j, sponsorSle, waiveFee);
         },
         [&](MPTIssue const&) {
             return accountSendMPT(

src/libxrpl/protocol/Indexes.cpp

@@ -84,6 +84,7 @@ enum class LedgerNameSpace : std::uint16_t {
     Vault = 'V',
     LoanBroker = 'l',  // lower-case L
     Loan = 'L',
+    Sponsorship = '>',
 
     // No longer used or supported. Left here to reserve the space to avoid accidental reuse.
     Contract [[deprecated]] = 'c',
@@ -326,6 +327,12 @@ signerList(AccountID const& account) noexcept
     return signerList(account, 0);
 }
 
+Keylet
+sponsorship(AccountID const& sponsor, AccountID const& sponsee) noexcept
+{
+    return {ltSPONSORSHIP, indexHash(LedgerNameSpace::Sponsorship, sponsor, sponsee)};
+}
+
 Keylet
 check(AccountID const& id, std::uint32_t seq) noexcept
 {

src/libxrpl/protocol/InnerObjectFormats.cpp

@@ -160,6 +160,14 @@ InnerObjectFormats::InnerObjectFormats()
             {sfTxnSignature, SoeOptional},
             {sfSigners, SoeOptional},
         });
+
+    add(sfSponsorSignature.jsonName.cStr(),
+        sfSponsorSignature.getCode(),
+        {
+            {sfSigningPubKey, SoeOptional},
+            {sfTxnSignature, SoeOptional},
+            {sfSigners, SoeOptional},
+        });
 }
 
 InnerObjectFormats const&

src/libxrpl/protocol/LedgerFormats.cpp

@@ -15,6 +15,7 @@ LedgerFormats::getCommonFields()
         {sfLedgerIndex, SoeOptional},
         {sfLedgerEntryType, SoeRequired},
         {sfFlags, SoeRequired},
+        {sfSponsor, SoeOptional},
     };
     return kCommonFields;
 }

src/libxrpl/protocol/STObject.cpp

@@ -634,16 +634,16 @@ STObject::getAccountID(SField const& field) const
 }
 
 AccountID
-STObject::getFeePayer() const
+STObject::getInitiator() const
 {
-    // If sfDelegate is present, the delegate account is the payer
+    // If sfDelegate is present, the delegate account is the initiator
     // note: if a delegate is specified, its authorization to act on behalf of the account is
     // enforced in `Transactor::invokeCheckPermission`
     // cryptographic signature validity is checked separately (e.g., in `Transactor::checkSign`)
     if (isFieldPresent(sfDelegate))
         return getAccountID(sfDelegate);
 
-    // Default payer
+    // Default initiator
     return getAccountID(sfAccount);
 }
 

src/libxrpl/protocol/STTx.cpp

@@ -28,6 +28,7 @@
 #include <xrpl/protocol/SeqProxy.h>
 #include <xrpl/protocol/Serializer.h>
 #include <xrpl/protocol/Sign.h>
+#include <xrpl/protocol/TxFlags.h>
 #include <xrpl/protocol/TxFormats.h>
 #include <xrpl/protocol/jss.h>
 
@@ -271,6 +272,13 @@ STTx::checkSign(Rules const& rules) const
             return std::unexpected("Counterparty: " + ret.error());
     }
 
+    if (isFieldPresent(sfSponsorSignature))
+    {
+        auto const sponsorSignatureObj = getFieldObject(sfSponsorSignature);
+        if (auto const ret = checkSign(rules, sponsorSignatureObj); !ret)
+            return std::unexpected("Sponsor: " + ret.error());
+    }
+
     // Verify the batch signer signatures here too, so they are cached with the
     // rest of signature checking (checkValidity / SF_SIGGOOD) and stay out of
     // the transaction engine. Gated on a batch (batchTxnIds_ seated) that
@@ -551,7 +559,7 @@ STTx::checkMultiSign(Rules const& rules, STObject const& sigObject) const
     // For delegated transactions sfDelegate is the account whose signer list is checked,
     // the delegate account itself can not be among the signers.
     auto const txnAccountID =
-        &sigObject != this ? std::nullopt : std::optional<AccountID>(getFeePayer());
+        &sigObject != this ? std::nullopt : std::optional<AccountID>(getInitiator());
 
     // We can ease the computational load inside the loop a bit by
     // pre-constructing part of the data that we hash.  Fill a Serializer
@@ -603,6 +611,15 @@ STTx::getBatchTransactionIDs() const
     return *batchTxnIds_;
 }
 
+AccountID
+STTx::getFeePayerID() const
+{
+    if (isFieldPresent(sfSponsor) && ((getFieldU32(sfSponsorFlags) & spfSponsorFee) != 0u))
+        return at(sfSponsor);
+
+    return getInitiator();
+}
+
 //------------------------------------------------------------------------------
 
 static bool

src/libxrpl/protocol/TER.cpp

@@ -107,6 +107,7 @@ transResults()
         MAKE_ERROR(tecPSEUDO_ACCOUNT,                "This operation is not allowed against a pseudo-account."),
         MAKE_ERROR(tecPRECISION_LOSS,                "The amounts used by the transaction cannot interact."),
         MAKE_ERROR(tecBAD_PROOF,                     "Proof cannot be verified"),
+        MAKE_ERROR(tecNO_SPONSOR_PERMISSION,         "Sponsor has not authorized this transaction."),
 
         MAKE_ERROR(tefALREADY,                     "The exact transaction was already in this ledger."),
         MAKE_ERROR(tefBAD_ADD_AUTH,                "Not authorized to add account."),
@@ -220,6 +221,7 @@ transResults()
         MAKE_ERROR(terADDRESS_COLLISION,      "Failed to allocate an unique account address."),
         MAKE_ERROR(terNO_DELEGATE_PERMISSION, "Delegated account lacks permission to perform this transaction."),
         MAKE_ERROR(terLOCKED,                 "Fund is locked."),
+        MAKE_ERROR(terNO_PERMISSION,          "No permission to perform requested operation."),
 
         MAKE_ERROR(tesSUCCESS,                "The transaction was applied. Only final in a validated ledger."),
     };

src/libxrpl/protocol/TxFormats.cpp

@@ -30,6 +30,9 @@ TxFormats::getCommonFields()
         {sfSigners, SoeOptional},  // submit_multisigned
         {sfNetworkID, SoeOptional},
         {sfDelegate, SoeOptional},
+        {sfSponsor, SoeOptional},
+        {sfSponsorFlags, SoeOptional},
+        {sfSponsorSignature, SoeOptional},
     };
     return kCommonFields;
 }

src/libxrpl/tx/Transactor.cpp

@@ -17,6 +17,7 @@
 #include <xrpl/ledger/helpers/NFTokenHelpers.h>
 #include <xrpl/ledger/helpers/OfferHelpers.h>
 #include <xrpl/ledger/helpers/RippleStateHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Feature.h>
 #include <xrpl/protocol/Indexes.h>
@@ -41,6 +42,7 @@
 #include <xrpl/tx/apply.h>
 #include <xrpl/tx/applySteps.h>
 
+#include <algorithm>
 #include <cstddef>
 #include <cstdint>
 #include <exception>
@@ -167,6 +169,58 @@ preflightCheckSimulateKeys(ApplyFlags flags, STObject const& sigObject, beast::J
 
 }  // namespace detail
 
+static NotTEC
+preflight1Sponsor(PreflightContext const& ctx)
+{
+    bool const hasSponsor = ctx.tx.isFieldPresent(sfSponsor);
+    bool const hasSponsorFlags = ctx.tx.isFieldPresent(sfSponsorFlags);
+    bool const hasSponsorSig = ctx.tx.isFieldPresent(sfSponsorSignature);
+
+    if ((hasSponsor || hasSponsorFlags || hasSponsorSig) && !ctx.rules.enabled(featureSponsor))
+        return temDISABLED;
+
+    if (hasSponsor != hasSponsorFlags)
+    {
+        JLOG(ctx.j.debug()) << "preflight1: sponsor and sponsor flags mismatch";
+        return temINVALID_FLAG;
+    }
+    if (hasSponsorSig && (!hasSponsor || !hasSponsorFlags))
+    {
+        JLOG(ctx.j.debug()) << "preflight1: sponsor signature without sponsor definition";
+        return temMALFORMED;
+    }
+
+    if (hasSponsorFlags)
+    {
+        auto const sponsorFlags = ctx.tx.getFieldU32(sfSponsorFlags);
+        if (((sponsorFlags & spfSponsorFlagMask) != 0u) || sponsorFlags == 0)
+        {
+            JLOG(ctx.j.debug()) << "preflight1: invalid sponsor flags";
+            return temINVALID_FLAG;
+        }
+
+        // Reserve sponsorship is only permitted for an explicit allow-list of
+        // transaction types, for v1. All other tx types reject spfSponsorReserve here.
+        if (isReserveSponsored(ctx.tx))
+        {
+            if (!isReserveSponsorAllowed(ctx.tx.getTxnType()))
+            {
+                JLOG(ctx.j.debug())
+                    << "preflight1: spfSponsorReserve not allowed for this transaction type";
+                return temINVALID_FLAG;
+            }
+        }
+    }
+
+    if (hasSponsor && ctx.tx.getAccountID(sfSponsor) == ctx.tx.getAccountID(sfAccount))
+    {
+        JLOG(ctx.j.debug()) << "preflight1: Sponsor account cannot be the same as the account";
+        return temMALFORMED;
+    }
+
+    return tesSUCCESS;
+}
+
 /** Performs early sanity checks on the account and fee fields */
 NotTEC
 Transactor::preflight1(PreflightContext const& ctx, std::uint32_t flagMask)
@@ -230,6 +284,9 @@ Transactor::preflight1(PreflightContext const& ctx, std::uint32_t flagMask)
     if (ctx.tx.isFlag(tfInnerBatchTxn) != ctx.parentBatchId.has_value())
         return temINVALID_INNER_BATCH;
 
+    if (auto const ter = preflight1Sponsor(ctx); !isTesSuccess(ter))
+        return ter;
+
     return tesSUCCESS;
 }
 
@@ -343,6 +400,44 @@ Transactor::checkPermission(
     return tesSUCCESS;
 }
 
+NotTEC
+Transactor::checkSponsor(ReadView const& view, STTx const& tx)
+{
+    if (!tx.isFieldPresent(sfSponsor))
+        return tesSUCCESS;
+
+    // Reserve sponsorship with permissioned delegation is disallowed.
+    if (tx.isFieldPresent(sfDelegate) && isReserveSponsored(tx))
+        return temINVALID;
+
+    if (!view.exists(keylet::account(tx.getAccountID(sfSponsor))))
+        return terNO_ACCOUNT;
+
+    // Skip Sponsorship existence checks if the sponsor has signed the transaction - this
+    // transaction is valid regardless of the Sponsorship object.
+    // The use of the Sponsorship object is properly handled in
+    // getFeePayer/checkReserve/increaseOwnerCount/decreaseOwnerCount.
+    if (tx.isFieldPresent(sfSponsorSignature))
+        return tesSUCCESS;
+
+    // If the transaction contains sfDelegate, the Sponsorship object should be
+    // between the sponsor and the delegate.
+    auto const sponsorshipSle =
+        view.read(keylet::sponsorship(tx.getAccountID(sfSponsor), tx.getInitiator()));
+
+    // sponsorship object missing for pre-funded (no co-signing) tx
+    if (!sponsorshipSle)
+        return terNO_PERMISSION;
+
+    if (isFeeSponsored(tx) && sponsorshipSle->isFlag(lsfSponsorshipRequireSignForFee))
+        return terNO_PERMISSION;
+
+    if (isReserveSponsored(tx) && sponsorshipSle->isFlag(lsfSponsorshipRequireSignForReserve))
+        return terNO_PERMISSION;
+
+    return tesSUCCESS;
+}
+
 XRPAmount
 Transactor::calculateBaseFee(ReadView const& view, STTx const& tx)
 {
@@ -351,6 +446,7 @@ Transactor::calculateBaseFee(ReadView const& view, STTx const& tx)
     // The computation has two parts:
     //  * The base fee, which is the same for most transactions.
     //  * The additional cost of each multisignature on the transaction.
+    //  * The additional cost of each multisignature on the sponsor.
     XRPAmount const baseFee = view.fees().base;
 
     // Each signer adds one more baseFee to the minimum required fee
@@ -358,7 +454,15 @@ Transactor::calculateBaseFee(ReadView const& view, STTx const& tx)
     std::size_t const signerCount =
         tx.isFieldPresent(sfSigners) ? tx.getFieldArray(sfSigners).size() : 0;
 
-    return baseFee + (signerCount * baseFee);
+    std::size_t sponsorSignerCount = 0;
+    if (tx.isFieldPresent(sfSponsorSignature))
+    {
+        auto const sponsorObj = tx.getFieldObject(sfSponsorSignature);
+        if (sponsorObj.isFieldPresent(sfSigners))
+            sponsorSignerCount += sponsorObj.getFieldArray(sfSigners).size();
+    }
+
+    return baseFee + ((signerCount + sponsorSignerCount) * baseFee);
 }
 
 XRPAmount
@@ -437,12 +541,51 @@ Transactor::checkFee(PreclaimContext const& ctx, XRPAmount baseFee)
     if (feePaid == beast::kZero)
         return tesSUCCESS;
 
-    auto const id = ctx.tx.getFeePayer();
-    auto const sle = ctx.view.read(keylet::account(id));
-    if (!sle)
-        return terNO_ACCOUNT;
+    auto const feePayer = getFeePayer(ctx.view, ctx.tx);
+    auto const payerSle = ctx.view.read(feePayer.keylet);
 
-    auto const balance = (*sle)[sfBalance].xrp();
+    if (!payerSle)
+    {
+        if (feePayer.type == FeePayerType::SponsorPreFunded)
+        {
+            // Sanity check: already checked in checkSponsor
+            return tefINTERNAL;  // LCOV_EXCL_LINE
+        }
+
+        return terNO_ACCOUNT;
+    }
+
+    XRPAmount maxSpendable = beast::kZero;
+
+    if (feePayer.type == FeePayerType::SponsorPreFunded)
+    {
+        if (payerSle->getType() != ltSPONSORSHIP)
+            return tefINTERNAL;  // LCOV_EXCL_LINE
+
+        if (payerSle->isFieldPresent(feePayer.balanceField))
+            maxSpendable = payerSle->getFieldAmount(feePayer.balanceField).xrp();
+
+        if (payerSle->isFieldPresent(sfMaxFee))
+        {
+            auto const cap = payerSle->getFieldAmount(sfMaxFee).xrp();
+            maxSpendable = std::min(maxSpendable, cap);
+        }
+    }
+    else
+    {
+        if (payerSle->getType() != ltACCOUNT_ROOT)
+            return tefINTERNAL;  // LCOV_EXCL_LINE
+
+        if (feePayer.type == FeePayerType::SponsorCoSigned)
+        {
+            auto const sponsorReserve = accountReserve(ctx.view, payerSle, ctx.j);
+            maxSpendable = payerSle->getFieldAmount(sfBalance).xrp() - sponsorReserve;
+        }
+        else
+        {
+            maxSpendable = payerSle->getFieldAmount(feePayer.balanceField).xrp();
+        }
+    }
 
     // NOTE: Because preclaim evaluates against a static readview, it
     // does not reflect fee deductions from other transactions paid by
@@ -451,12 +594,12 @@ Transactor::checkFee(PreclaimContext const& ctx, XRPAmount baseFee)
     // transactions, this check may pass optimistically.
     // The fee shortfall will be handled by the Transactor::reset mechanism,
     // which caps the fee to the remaining actual balance.
-    if (balance < feePaid)
+    if (maxSpendable < feePaid)
     {
-        JLOG(ctx.j.trace()) << "Insufficient balance:" << " balance=" << to_string(balance)
+        JLOG(ctx.j.trace()) << "Insufficient balance:" << " balance=" << to_string(maxSpendable)
                             << " paid=" << to_string(feePaid);
 
-        if ((balance > beast::kZero) && !ctx.view.open())
+        if ((maxSpendable > beast::kZero) && !ctx.view.open())
         {
             // Closed ledger, non-zero balance, less than fee
             return tecINSUFF_FEE;
@@ -473,16 +616,72 @@ Transactor::payFee()
 {
     auto const feePaid = ctx_.tx[sfFee].xrp();
 
-    auto const feePayer = ctx_.tx.getFeePayer();
-    auto const sle = view().peek(keylet::account(feePayer));
+    auto const feePayer = getFeePayer(view(), ctx_.tx);
+    auto const sle = view().peek(feePayer.keylet);
+
+    JLOG(j_.trace()) << "Fee payer: " + to_string(feePayer.id);
+
     if (!sle)
         return tefINTERNAL;  // LCOV_EXCL_LINE
 
-    // Deduct the fee, so it's not available during the transaction.
-    // Will only write the account back if the transaction succeeds.
-    sle->setFieldAmount(sfBalance, sle->getFieldAmount(sfBalance) - feePaid);
-    if (feePayer != accountID_)
-        view().update(sle);  // done in `apply()` for the account
+    if (feePaid == beast::kZero)
+        return tesSUCCESS;
+
+    XRPAmount balance = beast::kZero;
+    if (sle->isFieldPresent(feePayer.balanceField))
+    {
+        balance = sle->getFieldAmount(feePayer.balanceField).xrp();
+    }
+    else if (feePayer.balanceField != sfFeeAmount)
+    {
+        return tefINTERNAL;  // LCOV_EXCL_LINE
+    }
+
+    // A co-signed sponsor pays the fee out of its own account balance, but must
+    // never be charged into its account reserve, and a pre-funded sponsorship's
+    // fee is capped by sfMaxFee. Mirror the spendable amount computed in
+    // checkFee() so both limits are enforced on the apply path too.
+    XRPAmount spendable = balance;
+    if (feePayer.type == FeePayerType::SponsorCoSigned)
+    {
+        auto const sponsorReserve = accountReserve(view(), sle, j_);
+        // max(balance - reserve, 0) with overflow handling
+        spendable = balance > sponsorReserve ? balance - sponsorReserve : beast::kZero;
+    }
+    else if (feePayer.type == FeePayerType::SponsorPreFunded && sle->isFieldPresent(sfMaxFee))
+    {
+        auto const cap = sle->getFieldAmount(sfMaxFee).xrp();
+        spendable = std::min(spendable, cap);
+    }
+
+    // Only sponsor fee-payers reject here on insufficient funds. For an
+    // ordinary account, the fee falls through and is capped by reset(), which
+    // caps to the account's balance. That capping is wrong for sponsors: a
+    // co-signed sponsor would be charged into its own reserve, and a prefunded
+    // sponsorship's fee amount should be rejected rather than partially spent.
+    if (feePaid > spendable &&
+        (feePayer.type == FeePayerType::SponsorPreFunded ||
+         feePayer.type == FeePayerType::SponsorCoSigned))
+    {
+        if ((spendable > beast::kZero) && !view().open())
+            return tecINSUFF_FEE;
+
+        return terINSUF_FEE_B;
+    }
+
+    auto const feeAmountAfter = balance - feePaid;
+
+    if (feeAmountAfter == beast::kZero && feePayer.balanceField == sfFeeAmount)
+    {
+        // Because ltSponsorship.sfFeeAmount is soeOptional
+        sle->makeFieldAbsent(feePayer.balanceField);
+    }
+    else
+    {
+        sle->setFieldAmount(feePayer.balanceField, feeAmountAfter);
+    }
+
+    view().update(sle);
 
     // VFALCO Should we call view().rawDestroyXRP() here as well?
     return tesSUCCESS;
@@ -656,7 +855,7 @@ Transactor::ticketDelete(
     }
 
     // Update the Ticket owner's reserve.
-    adjustOwnerCount(view, sleAccount, -1, j);
+    decreaseOwnerCountForObject(view, sleAccount, sleTicket, 1, j);
 
     // Remove Ticket from ledger.
     view.erase(sleTicket);
@@ -750,6 +949,21 @@ Transactor::checkSign(
         return tesSUCCESS;
     }
 
+    if (sigObject.isFieldPresent(sfSponsorSignature))
+    {
+        // Co-signed sponsorship
+
+        // Sanity check: already checked in preflight1
+        if (!sigObject.isFieldPresent(sfSponsor))
+            return tefINTERNAL;  // LCOV_EXCL_LINE
+
+        auto const sponsorID = sigObject.getAccountID(sfSponsor);
+        auto const sponsorSignature = sigObject.getFieldObject(sfSponsorSignature);
+        if (auto const ret = checkSign(view, flags, std::nullopt, sponsorID, sponsorSignature, j);
+            !isTesSuccess(ret))
+            return ret;
+    }
+
     // If the pk is empty and not simulate or simulate and signers,
     // then we must be multi-signing.
     if (sigObject.isFieldPresent(sfSigners))
@@ -1079,11 +1293,38 @@ Transactor::reset(XRPAmount fee)
     if (!txnAcct)
         return {tefINTERNAL, beast::kZero};
 
-    auto const payerSle = view().peek(keylet::account(ctx_.tx.getFeePayer()));
+    auto const feePayer = getFeePayer(view(), ctx_.tx);
+    auto const payerSle = view().peek(feePayer.keylet);
+
     if (!payerSle)
         return {tefINTERNAL, beast::kZero};  // LCOV_EXCL_LINE
 
-    auto const balance = payerSle->getFieldAmount(sfBalance).xrp();
+    XRPAmount balance = beast::kZero;
+    if (payerSle->isFieldPresent(feePayer.balanceField))
+    {
+        balance = payerSle->getFieldAmount(feePayer.balanceField).xrp();
+    }
+    else if (feePayer.balanceField != sfFeeAmount)
+    {
+        return {tefINTERNAL, beast::kZero};  // LCOV_EXCL_LINE
+    }
+
+    if (feePayer.type == FeePayerType::SponsorPreFunded && payerSle->isFieldPresent(sfMaxFee))
+    {
+        auto const cap = payerSle->getFieldAmount(sfMaxFee).xrp();
+        fee = std::min(fee, cap);
+    }
+
+    // A co-signed sponsor must never be charged into its own account reserve,
+    // so the fee is capped to the balance above the reserve rather than to the
+    // full balance.
+    XRPAmount spendable = balance;
+    if (feePayer.type == FeePayerType::SponsorCoSigned)
+    {
+        auto const sponsorReserve = accountReserve(view(), payerSle, j_);
+        // max(balance - reserve, 0) with overflow handling
+        spendable = balance > sponsorReserve ? balance - sponsorReserve : beast::kZero;
+    }
 
     // balance should have already been checked in checkFee / preFlight.
     XRPL_ASSERT(
@@ -1093,8 +1334,8 @@ Transactor::reset(XRPAmount fee)
     // We retry/reject the transaction if the account balance is zero or
     // we're applying against an open ledger and the balance is less than
     // the fee
-    if (fee > balance)
-        fee = balance;
+    if (fee > spendable)
+        fee = spendable;
 
     // Since we reset the context, we need to charge the fee and update
     // the account's sequence number (or consume the Ticket) again.
@@ -1102,7 +1343,17 @@ Transactor::reset(XRPAmount fee)
     // If for some reason we are unable to consume the ticket or sequence
     // then the ledger is corrupted.  Rather than make things worse we
     // reject the transaction.
-    payerSle->setFieldAmount(sfBalance, balance - fee);
+    auto const feeAmountAfter = balance - fee;
+    if (feeAmountAfter == beast::kZero && feePayer.balanceField == sfFeeAmount)
+    {
+        // Because ltSponsorship.sfFeeAmount is soeOptional
+        payerSle->makeFieldAbsent(feePayer.balanceField);
+    }
+    else
+    {
+        payerSle->setFieldAmount(feePayer.balanceField, feeAmountAfter);
+    }
+
     TER const ter{consumeSeqProxy(txnAcct)};
     XRPL_ASSERT(isTesSuccess(ter), "xrpl::Transactor::reset : result is tesSUCCESS");
 
@@ -1116,6 +1367,48 @@ Transactor::reset(XRPAmount fee)
     return {ter, fee};
 }
 
+FeePayer
+Transactor::getFeePayer(ReadView const& view, STTx const& tx)
+{
+    if (tx.isFieldPresent(sfSponsor) && isFeeSponsored(tx))
+    {
+        auto const sponsorID = tx.getAccountID(sfSponsor);
+        auto const sponseeID = tx.getInitiator();
+        auto const sponsorshipKeylet = keylet::sponsorship(sponsorID, sponseeID);
+
+        // if pre-funded sponsorship exists, prefer it
+        if (view.exists(sponsorshipKeylet))
+        {
+            // pre funded
+            return FeePayer{
+                .id = sponsorID,
+                .keylet = sponsorshipKeylet,
+                .balanceField = sfFeeAmount,
+                .type = FeePayerType::SponsorPreFunded};
+        }
+
+        // Checked in Transactor::checkSponsor
+        XRPL_ASSERT(
+            tx.isFieldPresent(sfSponsorSignature),
+            "xrpl::getFeePayer has sponsor signature without a sponsorship object");
+
+        // co-signed
+        return FeePayer{
+            .id = sponsorID,
+            .keylet = keylet::account(sponsorID),
+            .balanceField = sfBalance,
+            .type = FeePayerType::SponsorCoSigned};
+    }
+
+    AccountID const payerID = tx.getInitiator();
+    auto const payerAccountKeylet = keylet::account(payerID);
+    auto const payerType =
+        tx.isFieldPresent(sfDelegate) ? FeePayerType::Delegate : FeePayerType::Account;
+
+    return FeePayer{
+        .id = payerID, .keylet = payerAccountKeylet, .balanceField = sfBalance, .type = payerType};
+}
+
 // The sole purpose of this function is to provide a convenient, named
 // location to set a breakpoint, to be used when replaying transactions.
 void

src/libxrpl/tx/applySteps.cpp

@@ -181,6 +181,9 @@ invokePreclaim(PreclaimContext const& ctx)
                         if (NotTEC const result = T::checkPriorTxAndLastLedger(ctx))
                             return result;
 
+                        if (NotTEC const result = T::checkSponsor(ctx.view, ctx.tx))
+                            return result;
+
                         if (NotTEC const result =
                                 Transactor::invokeCheckPermission<T>(ctx.view, ctx.tx))
                             return result;

src/libxrpl/tx/invariants/InvariantCheck.cpp

@@ -148,6 +148,15 @@ XRPNotCreated::visitEntry(bool isDelete, SLE::const_ref before, SLE::const_ref a
                 if (isXRP((*before)[sfAmount]))
                     drops_ -= (*before)[sfAmount].xrp().drops();
                 break;
+            case ltSPONSORSHIP:
+                if (before->isFieldPresent(sfFeeAmount))
+                {
+                    XRPL_ASSERT(
+                        isXRP((*before)[sfFeeAmount]),
+                        "XRPNotCreated::visitEntry : Sponsorship.FeeAmount is XRP");
+                    drops_ -= (*before)[sfFeeAmount].xrp().drops();
+                }
+                break;
             default:
                 break;
         }
@@ -168,6 +177,15 @@ XRPNotCreated::visitEntry(bool isDelete, SLE::const_ref before, SLE::const_ref a
                 if (!isDelete && isXRP((*after)[sfAmount]))
                     drops_ += (*after)[sfAmount].xrp().drops();
                 break;
+            case ltSPONSORSHIP:
+                if (!isDelete && after->isFieldPresent(sfFeeAmount))
+                {
+                    XRPL_ASSERT(
+                        isXRP((*after)[sfFeeAmount]),
+                        "XRPNotCreated::visitEntry : Sponsorship.FeeAmount is XRP");
+                    drops_ += (*after)[sfFeeAmount].xrp().drops();
+                }
+                break;
             default:
                 break;
         }
@@ -515,6 +533,20 @@ AccountRootsDeletedClean::finalize(
             if (enforce)
                 return false;
         }
+        // An account should not be deleted with sponsorship fields
+        if (after->isFieldPresent(sfSponsoredOwnerCount) ||
+            after->isFieldPresent(sfSponsoringOwnerCount) ||
+            after->isFieldPresent(sfSponsoringAccountCount) || after->isFieldPresent(sfSponsor))
+        {
+            JLOG(j.fatal()) << "Invariant failed: account deletion left "
+                               "behind a sponsorship field";
+            XRPL_ASSERT(
+                enforce,
+                "xrpl::AccountRootsDeletedClean::finalize : "
+                "deleted account has no sponsorship fields");
+            if (enforce)
+                return false;
+        }
         // Simple types
         for (auto const& [keyletfunc, _1, _2] : kDirectAccountKeylets)
         {
@@ -881,8 +913,10 @@ ValidPseudoAccounts::visitEntry(bool isDelete, SLE::const_ref before, SLE::const
             // 1. Exactly one of the pseudo-account fields is set.
             // 2. The sequence number is not changed.
             // 3. The lsfDisableMaster, lsfDefaultRipple, and lsfDepositAuth
-            // flags are set.
+            //    flags are set.
             // 4. The RegularKey is not set.
+            // 5. The SponsoredOwnerCount, SponsoringOwnerCount, SponsoringAccountCount, Sponsor
+            //    fields are not set.
             {
                 std::vector<SField const*> const& fields = getPseudoAccountFields();
 
@@ -908,6 +942,12 @@ ValidPseudoAccounts::visitEntry(bool isDelete, SLE::const_ref before, SLE::const
             {
                 errors_.emplace_back("pseudo-account has a regular key");
             }
+            if (after->isFieldPresent(sfSponsoredOwnerCount) ||
+                after->isFieldPresent(sfSponsoringOwnerCount) || after->isFieldPresent(sfSponsor) ||
+                after->isFieldPresent(sfSponsoringAccountCount))
+            {
+                errors_.emplace_back("pseudo-account has a sponsorship field");
+            }
         }
     }
 }

src/libxrpl/tx/invariants/SponsorshipInvariant.cpp

@@ -0,0 +1,158 @@
+#include <xrpl/tx/invariants/SponsorshipInvariant.h>
+//
+#include <xrpl/basics/Log.h>
+#include <xrpl/beast/utility/Journal.h>
+#include <xrpl/core/ServiceRegistry.h>
+#include <xrpl/ledger/ReadView.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
+#include <xrpl/protocol/LedgerFormats.h>
+#include <xrpl/protocol/SField.h>
+#include <xrpl/protocol/STTx.h>
+#include <xrpl/protocol/TER.h>
+#include <xrpl/protocol/XRPAmount.h>
+
+#include <cstdint>
+
+namespace xrpl {
+
+// Add new sponsorship-related invariants implementations
+void
+SponsorshipOwnerCountsMatch::visitEntry(bool isDelete, SLE::const_ref before, SLE::const_ref after)
+{
+    auto getSponsored = [](SLE::const_ref sle) -> std::uint32_t {
+        if (sle && sle->getType() == ltACCOUNT_ROOT)
+            return sle->getFieldU32(sfSponsoredOwnerCount);
+        return 0;
+    };
+    auto getSponsoring = [](SLE::const_ref sle) -> std::uint32_t {
+        if (sle && sle->getType() == ltACCOUNT_ROOT)
+            return sle->getFieldU32(sfSponsoringOwnerCount);
+        return 0;
+    };
+
+    auto getOwnerCount = [](SLE::const_ref sle) -> std::uint32_t {
+        if (sle && sle->getType() == ltACCOUNT_ROOT)
+            return sle->getFieldU32(sfOwnerCount);
+        return 0;
+    };
+
+    auto getSponsoredObjectOwnerCount = [&](SLE::const_ref sle) -> std::uint32_t {
+        if (!sle)
+            return 0;
+        switch (sle->getType())
+        {
+            case ltACCOUNT_ROOT:
+                return 0;
+            case ltRIPPLE_STATE: {
+                // A trust line can be reserve-sponsored independently on each
+                // side, so it may contribute up to two sponsored owner counts.
+                uint32_t ownerCount = 0;
+                if (sle->isFieldPresent(sfHighSponsor))
+                    ownerCount++;
+                if (sle->isFieldPresent(sfLowSponsor))
+                    ownerCount++;
+                return ownerCount;
+            }
+            default:
+                // Every other supported type carries a single sfSponsor field
+                // and contributes its full owner-count magnitude only when it is
+                // sponsored.
+                if (!sle->isFieldPresent(sfSponsor))
+                    return 0;
+                return getLedgerEntryOwnerCount(*sle);
+        }
+    };
+
+    // The values are implicitly casted to std::int64_t to calculate deltas.
+    std::int64_t const beforeSponsored = getSponsored(before);
+    std::int64_t const afterSponsored = getSponsored(after);
+    std::int64_t const beforeSponsoring = getSponsoring(before);
+    std::int64_t const afterSponsoring = getSponsoring(after);
+
+    std::int64_t const beforeSponsoredObjectOwnerCount = getSponsoredObjectOwnerCount(before);
+    std::int64_t const afterSponsoredObjectOwnerCount =
+        isDelete ? 0 : getSponsoredObjectOwnerCount(after);
+
+    deltaSponsoredOwnerCount_ += (afterSponsored - beforeSponsored);
+    deltaSponsoringOwnerCount_ += (afterSponsoring - beforeSponsoring);
+
+    deltaSponsoredObjectOwnerCount_ +=
+        (afterSponsoredObjectOwnerCount - beforeSponsoredObjectOwnerCount);
+
+    if (getOwnerCount(after) < getSponsored(after))
+        ownerCountBelowSponsored_ += 1;
+}
+
+bool
+SponsorshipOwnerCountsMatch::finalize(
+    STTx const&,
+    TER const,
+    XRPAmount const,
+    ReadView const&,
+    beast::Journal const& j) const
+{
+    if (deltaSponsoredOwnerCount_ != deltaSponsoringOwnerCount_)
+    {
+        JLOG(j.fatal()) << "Invariant failed: SponsoredOwnerCount does not "
+                           "equal SponsoringOwnerCount delta.";
+        return false;
+    }
+
+    if (ownerCountBelowSponsored_ > 0)
+    {
+        JLOG(j.fatal())
+            << "Invariant failed: OwnerCount must be greater than or equal to SponsoredOwnerCount.";
+        return false;
+    }
+
+    if (deltaSponsoredObjectOwnerCount_ != deltaSponsoredOwnerCount_)
+    {
+        JLOG(j.fatal()) << "Invariant failed: SponsoredObjectOwnerCount does not "
+                           "equal SponsoredOwnerCount delta.";
+        return false;
+    }
+
+    return true;
+}
+
+void
+SponsorshipAccountCountMatchesField::visitEntry(bool, SLE::const_ref before, SLE::const_ref after)
+{
+    auto getSponsoringAccountCount = [](SLE::const_ref sle) -> std::uint32_t {
+        if (sle && sle->getType() == ltACCOUNT_ROOT)
+            return sle->getFieldU32(sfSponsoringAccountCount);
+        return 0;
+    };
+
+    auto hasSponsorField = [](SLE::const_ref sle) -> bool {
+        return sle && sle->getType() == ltACCOUNT_ROOT && sle->isFieldPresent(sfSponsor);
+    };
+
+    std::int64_t const beforeCount = getSponsoringAccountCount(before);
+    std::int64_t const afterCount = getSponsoringAccountCount(after);
+    deltaSponsoringAccountCount_ += (afterCount - beforeCount);
+
+    int const beforePresent = hasSponsorField(before) ? 1 : 0;
+    int const afterPresent = hasSponsorField(after) ? 1 : 0;
+    deltaSponsorFieldPresence_ += (afterPresent - beforePresent);
+}
+
+bool
+SponsorshipAccountCountMatchesField::finalize(
+    STTx const&,
+    TER const,
+    XRPAmount const,
+    ReadView const&,
+    beast::Journal const& j) const
+{
+    if (deltaSponsoringAccountCount_ != deltaSponsorFieldPresence_)
+    {
+        JLOG(j.fatal()) << "Invariant failed: Net delta of SponsoringAccountCount does not "
+                           "match net delta of sfSponsor presence.";
+        return false;
+    }
+
+    return true;
+}
+
+}  // namespace xrpl

src/libxrpl/tx/invariants/VaultInvariant.cpp

@@ -222,7 +222,10 @@ ValidVault::deltaAssetsTxAccount(STTx const& tx, XRPAmount fee) const
     if (!ret.has_value() || !vaultAsset.native())
         return ret;
 
-    if (auto const delegate = tx[~sfDelegate]; delegate.has_value() && *delegate != tx[sfAccount])
+    // Only add the fee back if tx[sfAccount] actually paid it. When the fee is
+    // paid by someone else (a delegate or a fee sponsor), the
+    // account's XRP balance moved only by the vault amount.
+    if (tx.getFeePayerID() != tx[sfAccount])
         return ret;
 
     ret->delta += fee.drops();
@@ -1044,10 +1047,8 @@ ValidVault::finalize(
 
             case ttLOAN_SET:
             case ttLOAN_MANAGE:
-            case ttLOAN_PAY: {
-                // TBD
+            case ttLOAN_PAY:
                 return true;
-            }
 
             default:
                 // LCOV_EXCL_START

src/libxrpl/tx/paths/BookStep.cpp

@@ -731,7 +731,7 @@ BookStep<TIn, TOut, TDerived>::forEachOffer(
             // Create MPToken for the offer's owner. No need to check
             // for the reserve since the offer is removed if it is consumed.
             // Therefore, the owner count remains the same.
-            if (auto const err = checkCreateMPT(sb, assetIn.get<MPTIssue>(), owner, j_);
+            if (auto const err = checkCreateMPT(sb, assetIn.get<MPTIssue>(), owner, {}, j_);
                 !isTesSuccess(err))
             {
                 return true;

src/libxrpl/tx/paths/MPTEndpointStep.cpp

@@ -410,7 +410,8 @@ MPTEndpointOfferCrossingStep::checkCreateMPT(ApplyView& view, xrpl::DebtDirectio
         // for the reserve since the offer doesn't go on the books
         // if crossed. Insufficient reserve is allowed if the offer
         // crossed. See CreateOffer::applyGuts() for reserve check.
-        if (auto const err = xrpl::checkCreateMPT(view, mptIssue_, dst_, j_); !isTesSuccess(err))
+        if (auto const err = xrpl::checkCreateMPT(view, mptIssue_, dst_, {}, j_);
+            !isTesSuccess(err))
         {
             JLOG(j_.trace()) << "MPTEndpointStep::checkCreateMPT: failed create MPT";
             resetCache(srcDebtDir);

src/libxrpl/tx/transactors/account/AccountDelete.cpp

@@ -35,7 +35,6 @@
 #include <utility>
 
 namespace xrpl {
-
 bool
 AccountDelete::checkExtraFeatures(PreflightContext const& ctx)
 {
@@ -268,6 +267,15 @@ AccountDelete::preclaim(PreclaimContext const& ctx)
     if (cp)
         return tecHAS_OBLIGATIONS;
 
+    if (sleAccount->isFieldPresent(sfSponsor))
+    {
+        if (dst != sleAccount->getAccountID(sfSponsor))
+            return tecNO_SPONSOR_PERMISSION;
+    }
+    if (sleAccount->isFieldPresent(sfSponsoringOwnerCount) ||
+        sleAccount->isFieldPresent(sfSponsoringAccountCount))
+        return tecHAS_OBLIGATIONS;
+
     // We don't allow an account to be deleted if its sequence number
     // is within 256 of the current ledger.  This prevents replay of old
     // transactions if this account is resurrected after it is deleted.
@@ -394,6 +402,35 @@ AccountDelete::doApply()
     (*src)[sfBalance] = (*src)[sfBalance] - remainingBalance;
     ctx_.deliver(remainingBalance);
 
+    if (src->isFieldPresent(sfSponsor))
+    {
+        auto const sponsorID = src->getAccountID(sfSponsor);
+        auto sponsorSle = view().peek(keylet::account(sponsorID));
+
+        if (!sponsorSle)
+            return tefINTERNAL;  // LCOV_EXCL_LINE
+
+        auto const sponsoringAccountCount = sponsorSle->getFieldU32(sfSponsoringAccountCount);
+
+        XRPL_ASSERT(
+            sponsoringAccountCount != 0,
+            "xrpl::AccountDelete::doApply : sponsoring account count is present");
+        if (sponsoringAccountCount == 0)
+        {
+            // sanity check
+            // Since sfSponsoringAccountCount is set to soeDEFAULT, the field will not be
+            // present with a value of 0.
+            return tefINTERNAL;  // LCOV_EXCL_LINE
+        }
+        sponsorSle->at(sfSponsoringAccountCount) = sponsoringAccountCount - 1;
+        view().update(sponsorSle);
+
+        // Following line might look redundant, but without it, sfSponsor
+        // would end up remaining in after-ltAccountRoot during the
+        // InvariantCheck.
+        src->makeFieldAbsent(sfSponsor);
+    }
+
     XRPL_ASSERT(
         (*src)[sfBalance] == XRPAmount(0), "xrpl::AccountDelete::doApply : source balance is zero");
 

src/libxrpl/tx/transactors/account/SignerListSet.cpp

@@ -8,6 +8,7 @@
 #include <xrpl/ledger/ReadView.h>
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/DirectoryHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Feature.h>
 #include <xrpl/protocol/Indexes.h>
@@ -147,9 +148,7 @@ SignerListSet::preCompute()
     Transactor::preCompute();
 }
 
-// The return type is signed so it is compatible with the 3rd argument
-// of adjustOwnerCount() (which must be signed).
-static int
+static std::uint32_t
 signerCountBasedOwnerCountDelta(std::size_t entryCount, Rules const& rules)
 {
     // We always compute the full change in OwnerCount, taking into account:
@@ -165,7 +164,7 @@ signerCountBasedOwnerCountDelta(std::size_t entryCount, Rules const& rules)
     // units.  A SignerList with 8 entries would cost 10 OwnerCount units.
     //
     // The static_cast should always be safe since entryCount should always
-    // be in the range from 1 to 32.
+    // be in the range from 1 to 32, so the result is always positive.
     // We've got a lot of room to grow.
     XRPL_ASSERT(
         entryCount >= STTx::kMinMultiSigners,
@@ -196,12 +195,11 @@ removeSignersFromLedger(
     // There are two different ways that the OwnerCount could be managed.
     // If the lsfOneOwnerCount bit is set then remove just one owner count.
     // Otherwise use the pre-MultiSignReserve amendment calculation.
-    int removeFromOwnerCount = -1;
+    std::uint32_t removeFromOwnerCount = 1;
     if (!signers->isFlag(lsfOneOwnerCount))
     {
         STArray const& actualList = signers->getFieldArray(sfSignerEntries);
-        removeFromOwnerCount =
-            signerCountBasedOwnerCountDelta(actualList.size(), view.rules()) * -1;
+        removeFromOwnerCount = signerCountBasedOwnerCountDelta(actualList.size(), view.rules());
     }
 
     // Remove the node from the account directory.
@@ -215,8 +213,8 @@ removeSignersFromLedger(
         // LCOV_EXCL_STOP
     }
 
-    adjustOwnerCount(
-        view, view.peek(accountKeylet), removeFromOwnerCount, registry.getJournal("View"));
+    decreaseOwnerCountForObject(
+        view, view.peek(accountKeylet), signers, removeFromOwnerCount, registry.getJournal("View"));
 
     view.erase(signers);
 
@@ -315,19 +313,20 @@ SignerListSet::replaceSignerList()
     if (!sle)
         return tefINTERNAL;  // LCOV_EXCL_LINE
 
-    // Compute new reserve.  Verify the account has funds to meet the reserve.
-    std::uint32_t const oldOwnerCount{(*sle)[sfOwnerCount]};
-
     static constexpr int kAddedOwnerCount = 1;
     std::uint32_t const flags{lsfOneOwnerCount};
 
-    XRPAmount const newReserve{view().fees().accountReserve(oldOwnerCount + kAddedOwnerCount)};
-
     // We check the reserve against the starting balance because we want to
     // allow dipping into the reserve to pay fees.  This behavior is consistent
     // with TicketCreate.
-    if (preFeeBalance_ < newReserve)
-        return tecINSUFFICIENT_RESERVE;
+    if (auto const ret = checkReserve(
+            ctx_.getApplyViewContext(),
+            sle,
+            preFeeBalance_,
+            {.ownerCountDelta = kAddedOwnerCount},
+            ctx_.journal);
+        !isTesSuccess(ret))
+        return ret;
 
     // Everything's ducky.  Add the ltSIGNER_LIST to the ledger.
     auto signerList = std::make_shared<SLE>(signerListKeylet);
@@ -349,7 +348,8 @@ SignerListSet::replaceSignerList()
 
     // If we succeeded, the new entry counts against the
     // creator's reserve.
-    adjustOwnerCount(view(), sle, kAddedOwnerCount, viewJ);
+    increaseOwnerCount(ctx_.getApplyViewContext(), sle, kAddedOwnerCount, viewJ);
+    addSponsorToLedgerEntry(ctx_.getApplyViewContext(), signerList);
     return tesSUCCESS;
 }
 

src/libxrpl/tx/transactors/bridge/XChainBridge.cpp

@@ -435,8 +435,7 @@ transferHelper(
             return tecINTERNAL;  // LCOV_EXCL_LINE
 
         {
-            auto const ownerCount = sleSrc->getFieldU32(sfOwnerCount);
-            auto const reserve = psb.fees().accountReserve(ownerCount);
+            auto const reserve = accountReserve(psb, sleSrc, j);
 
             auto const availableBalance = [&]() -> STAmount {
                 STAmount curBal = (*sleSrc)[sfBalance];
@@ -726,9 +725,8 @@ finalizeClaimHelper(
             }
 
             // Remove the claim id from the ledger
+            decreaseOwnerCountForObject(outerSb, sleOwner, sleClaimID, 1, j);
             outerSb.erase(sleClaimID);
-
-            adjustOwnerCount(outerSb, sleOwner, -1, j);
         }
     }
 
@@ -1028,7 +1026,7 @@ applyCreateAccountAttestations(
 
             // Check reserve
             auto const balance = (*sleDoor)[sfBalance];
-            auto const reserve = psb.fees().accountReserve((*sleDoor)[sfOwnerCount] + 1);
+            auto const reserve = accountReserve(psb, sleDoor, j, {.ownerCountDelta = 1});
 
             if (balance < reserve)
                 return std::unexpected(tecINSUFFICIENT_RESERVE);
@@ -1137,7 +1135,7 @@ applyCreateAccountAttestations(
             return tecINTERNAL;  // LCOV_EXCL_LINE
 
         // Reserve was already checked
-        adjustOwnerCount(psb, sleDoor, 1, j);
+        increaseOwnerCount(psb, sleDoor, {}, 1, j);
         psb.insert(createdSleClaimID);
         psb.update(sleDoor);
     }
@@ -1439,7 +1437,7 @@ XChainCreateBridge::preclaim(PreclaimContext const& ctx)
             return terNO_ACCOUNT;
 
         auto const balance = (*sleAcc)[sfBalance];
-        auto const reserve = ctx.view.fees().accountReserve((*sleAcc)[sfOwnerCount] + 1);
+        auto const reserve = accountReserve(ctx.view, sleAcc, ctx.j, {.ownerCountDelta = 1});
 
         if (balance < reserve)
             return tecINSUFFICIENT_RESERVE;
@@ -1484,7 +1482,7 @@ XChainCreateBridge::doApply()
         (*sleBridge)[sfOwnerNode] = *page;
     }
 
-    adjustOwnerCount(ctx_.view(), sleAcct, 1, ctx_.journal);
+    increaseOwnerCount(ctx_.view(), sleAcct, {}, 1, ctx_.journal);
 
     ctx_.view().insert(sleBridge);
     ctx_.view().update(sleAcct);
@@ -1987,8 +1985,7 @@ XChainCreateClaimID::preclaim(PreclaimContext const& ctx)
             return terNO_ACCOUNT;
 
         auto const balance = (*sleAcc)[sfBalance];
-        auto const reserve = ctx.view.fees().accountReserve((*sleAcc)[sfOwnerCount] + 1);
-
+        auto const reserve = accountReserve(ctx.view, sleAcc, ctx.j, {.ownerCountDelta = 1});
         if (balance < reserve)
             return tecINSUFFICIENT_RESERVE;
     }
@@ -2046,7 +2043,7 @@ XChainCreateClaimID::doApply()
         (*sleClaimID)[sfOwnerNode] = *page;
     }
 
-    adjustOwnerCount(ctx_.view(), sleAcct, 1, ctx_.journal);
+    increaseOwnerCount(ctx_.view(), sleAcct, {}, 1, ctx_.journal);
 
     ctx_.view().insert(sleClaimID);
     ctx_.view().update(sleBridge);

src/libxrpl/tx/transactors/check/CheckCancel.cpp

@@ -91,8 +91,7 @@ CheckCancel::doApply()
     }
 
     // If we succeeded, update the check owner's reserve.
-    auto const sleSrc = view().peek(keylet::account(srcId));
-    adjustOwnerCount(view(), sleSrc, -1, viewJ);
+    decreaseOwnerCountForObject(view(), srcId, sleCheck, 1, viewJ);
 
     // Remove check from ledger.
     view().erase(sleCheck);

src/libxrpl/tx/transactors/check/CheckCash.cpp

@@ -3,11 +3,13 @@
 #include <xrpl/basics/Log.h>
 #include <xrpl/basics/scope.h>
 #include <xrpl/core/ServiceRegistry.h>
+#include <xrpl/ledger/ApplyView.h>
 #include <xrpl/ledger/PaymentSandbox.h>
 #include <xrpl/ledger/View.h>
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/MPTokenHelpers.h>
 #include <xrpl/ledger/helpers/RippleStateHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/ledger/helpers/TokenHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Asset.h>
@@ -30,7 +32,7 @@
 #include <xrpl/tx/paths/detail/Steps.h>
 
 #include <algorithm>
-#include <cstdint>
+#include <memory>
 #include <optional>
 
 namespace xrpl {
@@ -175,7 +177,7 @@ CheckCash::preclaim(PreclaimContext const& ctx)
             // once the check is cashed, since the check's reserve will no
             // longer be required.  So, if we're dealing in XRP, we add one
             // reserve's worth to the available funds.
-            if (value.native())
+            if (value.native() && !sleCheck->isFieldPresent(sfSponsor))
                 availableFunds += XRPAmount{ctx.view.fees().increment};
 
             if (value > availableFunds)
@@ -307,6 +309,8 @@ CheckCash::doApply()
         // LCOV_EXCL_STOP
     }
 
+    auto const sponsorCheckSle = getLedgerEntryReserveSponsor(psb, sleCheck);
+
     // Preclaim already checked that source has at least the requested
     // funds.
     //
@@ -335,7 +339,7 @@ CheckCash::doApply()
             // from src's directory, we allow them to send that additional
             // incremental reserve amount in the transfer.  Hence the -1
             // argument.
-            STAmount const srcLiquid{xrpLiquid(psb, srcId, -1, viewJ)};
+            STAmount const srcLiquid{xrpLiquid(psb, srcId, sponsorCheckSle ? 0 : -1, viewJ)};
 
             // Now, how much do they need in order to be successful?
             STAmount const xrpDeliver{
@@ -385,14 +389,25 @@ CheckCash::doApply()
             STAmount const flowDeliver{
                 optDeliverMin ? maxDeliverMin() : ctx_.tx.getFieldAmount(sfAmount)};
 
+            auto applyViewContext = ApplyViewContext({.view = psb, .tx = ctx_.tx});
+            auto const sponsorSle = getTxReserveSponsor(applyViewContext);
+            if (!sponsorSle)
+                return sponsorSle.error();  // LCOV_EXCL_LINE
+
             // Check reserve. Return destination account SLE if enough reserve,
             // otherwise return nullptr.
-            auto checkReserve = [&]() -> SLE::pointer {
+            auto checkDstReserve = [&]() -> SLE::pointer {
                 auto sleDst = psb.peek(keylet::account(accountID_));
 
                 // Can the account cover the trust line's or MPT reserve?
-                if (std::uint32_t const ownerCount = {sleDst->at(sfOwnerCount)};
-                    preFeeBalance_ < psb.fees().accountReserve(ownerCount + 1))
+                if (auto const ret = checkReserve(
+                        applyViewContext,
+                        sleDst,
+                        preFeeBalance_,
+                        *sponsorSle,
+                        {.ownerCountDelta = 1},
+                        j_);
+                    !isTesSuccess(ret))
                 {
                     JLOG(j_.trace()) << "Trust line does not exist. "
                                         "Insufficient reserve to create line.";
@@ -426,7 +441,7 @@ CheckCash::doApply()
                         //     a. this (destination) account and
                         //     b. issuing account (not sending account).
 
-                        auto const sleDst = checkReserve();
+                        auto const sleDst = checkDstReserve();
                         if (sleDst == nullptr)
                             return tecNO_LINE_INSUF_RESERVE;
 
@@ -449,6 +464,7 @@ CheckCash::doApply()
                                 Issue(currency, accountID_),        // limit of zero
                                 0,                                  // quality in
                                 0,                                  // quality out
+                                *sponsorSle,                        // sponsor
                                 viewJ);                             // journal
                             !isTesSuccess(ter))
                         {
@@ -491,11 +507,12 @@ CheckCash::doApply()
                         auto const mptokenKey = keylet::mptoken(mptID, accountID_);
                         if (!psb.exists(mptokenKey))
                         {
-                            auto sleDst = checkReserve();
+                            auto sleDst = checkDstReserve();
                             if (sleDst == nullptr)
                                 return tecINSUFFICIENT_RESERVE;
 
-                            if (auto const err = checkCreateMPT(psb, mptID, accountID_, j_);
+                            if (auto const err =
+                                    checkCreateMPT(psb, mptID, accountID_, *sponsorSle, j_);
                                 !isTesSuccess(err))
                             {
                                 return err;
@@ -581,7 +598,7 @@ CheckCash::doApply()
     }
 
     // If we succeeded, update the check owner's reserve.
-    adjustOwnerCount(psb, psb.peek(keylet::account(srcId)), -1, viewJ);
+    decreaseOwnerCountForObject(psb, srcId, sleCheck, 1, viewJ);
 
     // Remove check from ledger.
     psb.erase(sleCheck);

src/libxrpl/tx/transactors/check/CheckCreate.cpp

@@ -7,6 +7,7 @@
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/DirectoryHelpers.h>
 #include <xrpl/ledger/helpers/MPTokenHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/ledger/helpers/TokenHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Asset.h>
@@ -194,13 +195,10 @@ CheckCreate::doApply()
     // A check counts against the reserve of the issuing account, but we
     // check the starting balance because we want to allow dipping into the
     // reserve to pay fees.
-    {
-        STAmount const reserve{view().fees().accountReserve(sle->getFieldU32(sfOwnerCount) + 1)};
-
-        if (preFeeBalance_ < reserve)
-            return tecINSUFFICIENT_RESERVE;
-    }
-
+    if (auto const ret = checkReserve(
+            ctx_.getApplyViewContext(), sle, preFeeBalance_, {.ownerCountDelta = 1}, ctx_.journal);
+        !isTesSuccess(ret))
+        return ret;
     // Note that we use the value from the sequence or ticket as the
     // Check sequence.  For more explanation see comments in SeqProxy.h.
     std::uint32_t const seq = ctx_.tx.getSeqValue();
@@ -253,7 +251,9 @@ CheckCreate::doApply()
         sleCheck->setFieldU64(sfOwnerNode, *page);
     }
     // If we succeeded, the new entry counts against the creator's reserve.
-    adjustOwnerCount(view(), sle, 1, viewJ);
+
+    increaseOwnerCount(ctx_.getApplyViewContext(), sle, 1, viewJ);
+    addSponsorToLedgerEntry(ctx_.getApplyViewContext(), sleCheck);
     return tesSUCCESS;
 }
 

src/libxrpl/tx/transactors/credentials/CredentialAccept.cpp

@@ -4,6 +4,7 @@
 #include <xrpl/ledger/ApplyView.h>
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/CredentialHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Feature.h>
 #include <xrpl/protocol/Indexes.h>
@@ -11,7 +12,6 @@
 #include <xrpl/protocol/LedgerFormats.h>
 #include <xrpl/protocol/Protocol.h>
 #include <xrpl/protocol/SField.h>
-#include <xrpl/protocol/STAmount.h>
 #include <xrpl/protocol/STLedgerEntry.h>
 #include <xrpl/protocol/STTx.h>
 #include <xrpl/protocol/TER.h>
@@ -93,12 +93,19 @@ CredentialAccept::doApply()
     if (!sleSubject || !sleIssuer)
         return tefINTERNAL;  // LCOV_EXCL_LINE
 
-    {
-        STAmount const reserve{
-            view().fees().accountReserve(sleSubject->getFieldU32(sfOwnerCount) + 1)};
-        if (preFeeBalance_ < reserve)
-            return tecINSUFFICIENT_RESERVE;
-    }
+    auto txSponsorSle = getTxReserveSponsor(ctx_.getApplyViewContext());
+    if (!txSponsorSle)
+        return txSponsorSle.error();  // LCOV_EXCL_LINE
+
+    if (auto const ret = checkReserve(
+            ctx_.getApplyViewContext(),
+            sleSubject,
+            preFeeBalance_,
+            *txSponsorSle,
+            {.ownerCountDelta = 1},
+            j_);
+        !isTesSuccess(ret))
+        return ret;
 
     auto const credType(ctx_.tx[sfCredentialType]);
     Keylet const credentialKey = keylet::credential(accountID_, issuer, credType);
@@ -115,10 +122,16 @@ CredentialAccept::doApply()
     }
 
     sleCred->setFieldU32(sfFlags, lsfAccepted);
-    view().update(sleCred);
 
-    adjustOwnerCount(view(), sleIssuer, -1, j_);
-    adjustOwnerCount(view(), sleSubject, 1, j_);
+    // Release the original creation sponsor from the credential (it covered
+    // the issuer's reserve), then assign the accept tx's sponsor (if any) so
+    // the credential reflects whoever is now covering the subject's reserve.
+    decreaseOwnerCountForObject(view(), sleIssuer, sleCred, 1, j_);
+    removeSponsorFromLedgerEntry(sleCred);
+
+    addSponsorToLedgerEntry(ctx_.getApplyViewContext(), sleCred);
+    increaseOwnerCount(ctx_.getApplyViewContext(), sleSubject, 1, j_);
+    view().update(sleCred);
 
     return tesSUCCESS;
 }

src/libxrpl/tx/transactors/credentials/CredentialCreate.cpp

@@ -7,13 +7,13 @@
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/CredentialHelpers.h>  // IWYU pragma: keep
 #include <xrpl/ledger/helpers/DirectoryHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/protocol/Feature.h>
 #include <xrpl/protocol/Indexes.h>
 #include <xrpl/protocol/Keylet.h>
 #include <xrpl/protocol/LedgerFormats.h>
 #include <xrpl/protocol/Protocol.h>
 #include <xrpl/protocol/SField.h>
-#include <xrpl/protocol/STAmount.h>
 #include <xrpl/protocol/STLedgerEntry.h>
 #include <xrpl/protocol/STTx.h>
 #include <xrpl/protocol/TER.h>
@@ -130,12 +130,10 @@ CredentialCreate::doApply()
     if (!sleIssuer)
         return tefINTERNAL;  // LCOV_EXCL_LINE
 
-    {
-        STAmount const reserve{
-            view().fees().accountReserve(sleIssuer->getFieldU32(sfOwnerCount) + 1)};
-        if (preFeeBalance_ < reserve)
-            return tecINSUFFICIENT_RESERVE;
-    }
+    if (auto const ret = checkReserve(
+            ctx_.getApplyViewContext(), sleIssuer, preFeeBalance_, {.ownerCountDelta = 1}, j_);
+        !isTesSuccess(ret))
+        return ret;
 
     sleCred->setAccountID(sfSubject, subject);
     sleCred->setAccountID(sfIssuer, accountID_);
@@ -153,7 +151,8 @@ CredentialCreate::doApply()
             return tecDIR_FULL;
         sleCred->setFieldU64(sfIssuerNode, *page);
 
-        adjustOwnerCount(view(), sleIssuer, 1, j_);
+        increaseOwnerCount(ctx_.getApplyViewContext(), sleIssuer, 1, j_);
+        addSponsorToLedgerEntry(ctx_.getApplyViewContext(), sleCred);
     }
 
     if (subject == accountID_)

src/libxrpl/tx/transactors/delegate/DelegateSet.cpp

@@ -5,10 +5,10 @@
 #include <xrpl/core/ServiceRegistry.h>
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/DirectoryHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/protocol/Indexes.h>
 #include <xrpl/protocol/Protocol.h>
 #include <xrpl/protocol/SField.h>
-#include <xrpl/protocol/STAmount.h>
 #include <xrpl/protocol/STLedgerEntry.h>
 #include <xrpl/protocol/STTx.h>
 #include <xrpl/protocol/TER.h>
@@ -98,11 +98,14 @@ DelegateSet::doApply()
     if (permissions.empty())
         return tecINTERNAL;  // LCOV_EXCL_LINE
 
-    STAmount const reserve{
-        ctx_.view().fees().accountReserve(sleOwner->getFieldU32(sfOwnerCount) + 1)};
-
-    if (preFeeBalance_ < reserve)
-        return tecINSUFFICIENT_RESERVE;
+    if (auto const ret = checkReserve(
+            ctx_.getApplyViewContext(),
+            sleOwner,
+            preFeeBalance_,
+            {.ownerCountDelta = 1},
+            ctx_.journal);
+        !isTesSuccess(ret))
+        return ret;
 
     sle = std::make_shared<SLE>(delegateKey);
     sle->setAccountID(sfAccount, accountID_);
@@ -130,7 +133,8 @@ DelegateSet::doApply()
     (*sle)[sfDestinationNode] = *destPage;
 
     ctx_.view().insert(sle);
-    adjustOwnerCount(ctx_.view(), sleOwner, 1, ctx_.journal);
+    increaseOwnerCount(ctx_.getApplyViewContext(), sleOwner, 1, ctx_.journal);
+    addSponsorToLedgerEntry(ctx_.getApplyViewContext(), sle);
 
     return tesSUCCESS;
 }
@@ -170,7 +174,7 @@ DelegateSet::deleteDelegate(ApplyView& view, SLE::ref sle, beast::Journal j)
     if (!sleOwner)
         return tecINTERNAL;  // LCOV_EXCL_LINE
 
-    adjustOwnerCount(view, sleOwner, -1, j);
+    decreaseOwnerCountForObject(view, sleOwner, sle, 1, j);
 
     view.erase(sle);
 

src/libxrpl/tx/transactors/dex/AMMCreate.cpp

@@ -332,17 +332,30 @@ applyCreate(ApplyContext& ctx, Sandbox& sb, AccountID const& account, beast::Jou
                     return err;
                 }
 
-                if (auto const err = createMPToken(sb, mptID, accountId, flags); !isTesSuccess(err))
+                if (auto const err = createMPToken(sb, mptID, accountId, {}, flags);
+                    !isTesSuccess(err))
                     return err;
                 // Don't adjust AMM owner count.
                 // It's irrelevant for pseudo-account like AMM.
                 return accountSend(
-                    sb, account, accountId, amount, ctx.journal, WaiveTransferFee::Yes);
+                    sb,
+                    account,
+                    accountId,
+                    amount,
+                    ctx.journal,
+                    {},  // don't sponsor for AMM Trustline
+                    WaiveTransferFee::Yes);
             },
             // Set AMM flag on AMM trustline
             [&](Issue const& issue) -> TER {
                 if (auto const res = accountSend(
-                        sb, account, accountId, amount, ctx.journal, WaiveTransferFee::Yes))
+                        sb,
+                        account,
+                        accountId,
+                        amount,
+                        ctx.journal,
+                        {},  // don't sponsor for AMM Trustline
+                        WaiveTransferFee::Yes))
                     return res;
                 // Set AMM flag on AMM trustline
                 if (!isXRP(amount))

src/libxrpl/tx/transactors/dex/AMMDeposit.cpp

@@ -618,7 +618,13 @@ AMMDeposit::deposit(
     }
 
     auto res = accountSend(
-        view, accountID_, ammAccount, amountDepositActual, ctx_.journal, WaiveTransferFee::Yes);
+        view,
+        accountID_,
+        ammAccount,
+        amountDepositActual,
+        ctx_.journal,
+        {},  // don't sponsor for AMM Trustline
+        WaiveTransferFee::Yes);
     if (!isTesSuccess(res))
     {
         JLOG(ctx_.journal.debug()) << "AMM Deposit: failed to deposit " << amountDepositActual;
@@ -642,6 +648,7 @@ AMMDeposit::deposit(
             ammAccount,
             *amount2DepositActual,
             ctx_.journal,
+            {},  // don't sponsor for AMM Trustline
             WaiveTransferFee::Yes);
         if (!isTesSuccess(res))
         {

src/libxrpl/tx/transactors/dex/AMMWithdraw.cpp

@@ -7,6 +7,7 @@
 #include <xrpl/core/ServiceRegistry.h>
 #include <xrpl/ledger/Sandbox.h>
 #include <xrpl/ledger/helpers/AMMHelpers.h>
+#include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/MPTokenHelpers.h>
 #include <xrpl/ledger/helpers/RippleStateHelpers.h>
 #include <xrpl/ledger/helpers/TokenHelpers.h>
@@ -658,15 +659,15 @@ AMMWithdraw::withdraw(
             auto sleAccount = view.peek(keylet::account(account));
             if (!sleAccount)
                 return tecINTERNAL;  // LCOV_EXCL_LINE
-            STAmount const balance = (*sleAccount)[sfBalance];
-            std::uint32_t const ownerCount = sleAccount->at(sfOwnerCount);
 
+            auto const balance = (*sleAccount)[sfBalance]->xrp();
             // See also TrustSet::doApply() and MPTokenAuthorize::authorize()
             XRPAmount const reserve(
-                (ownerCount < 2) ? XRPAmount(beast::kZero)
-                                 : view.fees().accountReserve(ownerCount + 1));
+                (ownerCount(sleAccount, journal) < 2)
+                    ? XRPAmount(beast::kZero)
+                    : accountReserve(view, sleAccount, journal, {.ownerCountDelta = 1}));
 
-            auto const balanceAdj = isIssue ? std::max(priorBalance, balance.xrp()) : priorBalance;
+            auto const balanceAdj = isIssue ? std::max(priorBalance, balance) : priorBalance;
             if (balanceAdj < reserve)
                 return tecINSUFFICIENT_RESERVE;
         }
@@ -683,7 +684,7 @@ AMMWithdraw::withdraw(
                 !isTesSuccess(err))
                 return err;
 
-            if (auto const err = checkCreateMPT(view, mptIssue, account, journal);
+            if (auto const err = checkCreateMPT(view, mptIssue, account, {}, journal);
                 !isTesSuccess(err))
             {
                 return err;
@@ -700,7 +701,7 @@ AMMWithdraw::withdraw(
 
     // Withdraw amountWithdraw
     auto res = accountSend(
-        view, ammAccount, account, amountWithdrawActual, journal, WaiveTransferFee::Yes);
+        view, ammAccount, account, amountWithdrawActual, journal, {}, WaiveTransferFee::Yes);
     if (!isTesSuccess(res))
     {
         // LCOV_EXCL_START
@@ -719,7 +720,7 @@ AMMWithdraw::withdraw(
             return {res, STAmount{}, STAmount{}, STAmount{}};
 
         res = accountSend(
-            view, ammAccount, account, *amount2WithdrawActual, journal, WaiveTransferFee::Yes);
+            view, ammAccount, account, *amount2WithdrawActual, journal, {}, WaiveTransferFee::Yes);
         if (!isTesSuccess(res))
         {
             // LCOV_EXCL_START

src/libxrpl/tx/transactors/dex/OfferCreate.cpp

@@ -833,9 +833,7 @@ OfferCreate::applyGuts(Sandbox& sb, Sandbox& sbCancel)
         return {tefINTERNAL, false};
 
     {
-        XRPAmount const reserve =
-            sb.fees().accountReserve(sleCreator->getFieldU32(sfOwnerCount) + 1);
-
+        XRPAmount const reserve = accountReserve(sb, sleCreator, viewJ, {.ownerCountDelta = 1});
         if (preFeeBalance_ < reserve)
         {
             // If we are here, the signing account had an insufficient reserve
@@ -869,7 +867,7 @@ OfferCreate::applyGuts(Sandbox& sb, Sandbox& sbCancel)
     }
 
     // Update owner count.
-    adjustOwnerCount(sb, sleCreator, 1, viewJ);
+    increaseOwnerCount(sb, sleCreator, {}, 1, viewJ);
 
     JLOG(j_.trace()) << "adding to book: " << to_string(saTakerPays.asset()) << " : "
                      << to_string(saTakerGets.asset())

src/libxrpl/tx/transactors/did/DIDDelete.cpp

@@ -50,8 +50,7 @@ DIDDelete::deleteSLE(ApplyView& view, SLE::pointer sle, AccountID const owner, b
     if (!sleOwner)
         return tecINTERNAL;  // LCOV_EXCL_LINE
 
-    adjustOwnerCount(view, sleOwner, -1, j);
-    view.update(sleOwner);
+    decreaseOwnerCountForObject(view, sleOwner, sle, 1, j);
 
     // Remove object from ledger
     view.erase(sle);

src/libxrpl/tx/transactors/did/DIDSet.cpp

@@ -72,7 +72,8 @@ addSLE(ApplyContext& ctx, SLE::ref sle, AccountID const& owner)
     // Check reserve availability for new object creation
     {
         auto const balance = STAmount((*sleAccount)[sfBalance]).xrp();
-        auto const reserve = ctx.view().fees().accountReserve((*sleAccount)[sfOwnerCount] + 1);
+        auto const reserve =
+            accountReserve(ctx.view(), sleAccount, ctx.journal, {.ownerCountDelta = 1});
 
         if (balance < reserve)
             return tecINSUFFICIENT_RESERVE;
@@ -89,7 +90,7 @@ addSLE(ApplyContext& ctx, SLE::ref sle, AccountID const& owner)
             return tecDIR_FULL;  // LCOV_EXCL_LINE
         (*sle)[sfOwnerNode] = *page;
     }
-    adjustOwnerCount(ctx.view(), sleAccount, 1, ctx.journal);
+    increaseOwnerCount(ctx.view(), sleAccount, {}, 1, ctx.journal);
     ctx.view().update(sleAccount);
 
     return tesSUCCESS;

src/libxrpl/tx/transactors/escrow/EscrowCancel.cpp

@@ -181,7 +181,7 @@ EscrowCancel::doApply()
         if (auto const ret = std::visit(
                 [&]<typename T>(T const&) {
                     return escrowUnlockApplyHelper<T>(
-                        ctx_.view(),
+                        ctx_.getApplyViewContext(),
                         kParityRate,
                         ctx_.view().rules().enabled(fixCleanup3_2_0) ? sle : slep,
                         preFeeBalance_,
@@ -209,8 +209,7 @@ EscrowCancel::doApply()
         }
     }
 
-    adjustOwnerCount(ctx_.view(), sle, -1, ctx_.journal);
-    ctx_.view().update(sle);
+    decreaseOwnerCountForObject(ctx_.view(), sle, slep, 1, ctx_.journal);
 
     // Remove escrow from ledger
     ctx_.view().erase(slep);

src/libxrpl/tx/transactors/escrow/EscrowCreate.cpp

@@ -11,6 +11,7 @@
 #include <xrpl/ledger/helpers/DirectoryHelpers.h>
 #include <xrpl/ledger/helpers/MPTokenHelpers.h>
 #include <xrpl/ledger/helpers/RippleStateHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/ledger/helpers/TokenHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Concepts.h>
@@ -434,16 +435,33 @@ EscrowCreate::doApply()
     // Check reserve and funds availability
     STAmount const amount{ctx_.tx[sfAmount]};
 
-    auto const reserve = ctx_.view().fees().accountReserve((*sle)[sfOwnerCount] + 1);
-
     auto const balance = sle->getFieldAmount(sfBalance).xrp();
-    if (balance < reserve)
-        return tecINSUFFICIENT_RESERVE;
+    // First check: whoever is on the hook for the new owner increment
+    // can cover it. When sponsored this hits the sponsor branch and
+    // validates the sponsor's reserve + remaining credit. When
+    // unsponsored this hits the source branch and validates the
+    // source's pre-lock balance against base + (currentOC+1)*increment.
+    if (auto const ret =
+            checkReserve(ctx_.getApplyViewContext(), sle, balance, {.ownerCountDelta = 1}, j_);
+        !isTesSuccess(ret))
+        return ret;
 
-    // Check reserve and funds availability
     if (isXRP(amount))
     {
-        if (balance < reserve + STAmount(amount).xrp())
+        // Second check (XRP escrow only): after locking the escrowed
+        // amount, the source must still meet its own reserve floor. This is
+        // always the source's own balance against the source's own reserve —
+        // the sponsor's reserve was already validated above, and a sponsor
+        // never covers the locked funds. We compare directly (rather than via
+        // checkReserve) because that helper diverts to the sponsor's balance
+        // when a sponsor is present and would ignore the source's post-lock
+        // balance entirely. ownerCountDelta differs by case:
+        // - sponsored:   0  — sponsor covers the new owner increment, so the
+        //                source only owes reserve for its current owners.
+        // - unsponsored: 1  — source owes reserve including the new increment.
+        auto const sourceReserve = accountReserve(
+            ctx_.view(), sle, j_, {.ownerCountDelta = getTxReserveSponsorID(ctx_.tx) ? 0 : 1});
+        if (balance - STAmount(amount).xrp() < sourceReserve)
             return tecUNFUNDED;
     }
 
@@ -535,7 +553,8 @@ EscrowCreate::doApply()
     }
 
     // increment owner count
-    adjustOwnerCount(ctx_.view(), sle, 1, ctx_.journal);
+    increaseOwnerCount(ctx_.getApplyViewContext(), sle, 1, ctx_.journal);
+    addSponsorToLedgerEntry(ctx_.getApplyViewContext(), slep);
     ctx_.view().update(sle);
     return tesSUCCESS;
 }

src/libxrpl/tx/transactors/escrow/EscrowFinish.cpp

@@ -340,6 +340,16 @@ EscrowFinish::doApply()
         }
     }
 
+    // With the Sponsor amendment, release the escrow reserve before delivery.
+    // Token delivery can auto-create a destination holding, and the same
+    // sponsor (or the same account, for a self-escrow) may cover both the
+    // escrow being removed and the holding being created. Without the
+    // amendment, keep the legacy order: releasing early changes the reserve
+    // arithmetic for self-escrows and would break consensus if not gated.
+    bool const sponsorEnabled = ctx_.view().rules().enabled(featureSponsor);
+    if (sponsorEnabled)
+        decreaseOwnerCountForObject(ctx_.view(), account, slep, 1, ctx_.journal);
+
     STAmount const amount = slep->getFieldAmount(sfAmount);
     // Transfer amount to destination
     if (isXRP(amount))
@@ -359,7 +369,7 @@ EscrowFinish::doApply()
         if (auto const ret = std::visit(
                 [&]<typename T>(T const&) {
                     return escrowUnlockApplyHelper<T>(
-                        ctx_.view(),
+                        ctx_.getApplyViewContext(),
                         lockedRate,
                         sled,
                         preFeeBalance_,
@@ -389,10 +399,9 @@ EscrowFinish::doApply()
 
     ctx_.view().update(sled);
 
-    // Adjust source owner count
-    auto const sle = ctx_.view().peek(keylet::account(account));
-    adjustOwnerCount(ctx_.view(), sle, -1, ctx_.journal);
-    ctx_.view().update(sle);
+    // Adjust source owner count (legacy position, pre-Sponsor)
+    if (!sponsorEnabled)
+        decreaseOwnerCountForObject(ctx_.view(), account, slep, 1, ctx_.journal);
 
     // Remove escrow from ledger
     ctx_.view().erase(slep);

src/libxrpl/tx/transactors/lending/LoanBrokerCoverClawback.cpp

@@ -372,7 +372,7 @@ LoanBrokerCoverClawback::doApply()
     associateAsset(*sleBroker, vaultAsset);
 
     // Transfer assets from pseudo-account to depositor.
-    return accountSend(view(), brokerPseudoID, account, clawAmount, j_, WaiveTransferFee::Yes);
+    return accountSend(view(), brokerPseudoID, account, clawAmount, j_, {}, WaiveTransferFee::Yes);
 }
 
 void

src/libxrpl/tx/transactors/lending/LoanBrokerCoverDeposit.cpp

@@ -176,7 +176,7 @@ LoanBrokerCoverDeposit::doApply()
 
     // Transfer assets from depositor to pseudo-account.
     if (auto ter =
-            accountSend(view(), accountID_, brokerPseudoID, amount, j_, WaiveTransferFee::Yes))
+            accountSend(view(), accountID_, brokerPseudoID, amount, j_, {}, WaiveTransferFee::Yes))
         return ter;
 
     // Increase the LoanBroker's CoverAvailable by Amount

src/libxrpl/tx/transactors/lending/LoanBrokerCoverWithdraw.cpp

@@ -211,7 +211,14 @@ LoanBrokerCoverWithdraw::doApply()
 
     associateAsset(*broker, vaultAsset);
 
-    return doWithdraw(view(), tx, accountID_, dstAcct, brokerPseudoID, preFeeBalance_, amount, j_);
+    return doWithdraw(
+        ctx_.getApplyViewContext(),
+        accountID_,
+        dstAcct,
+        brokerPseudoID,
+        preFeeBalance_,
+        amount,
+        j_);
 }
 
 void

src/libxrpl/tx/transactors/lending/LoanBrokerDelete.cpp

@@ -155,11 +155,11 @@ LoanBrokerDelete::doApply()
     {
         auto const coverAvailable = STAmount{vaultAsset, broker->at(sfCoverAvailable)};
         if (auto const ter = accountSend(
-                view(), brokerPseudoID, accountID_, coverAvailable, j_, WaiveTransferFee::Yes))
+                view(), brokerPseudoID, accountID_, coverAvailable, j_, {}, WaiveTransferFee::Yes))
             return ter;
     }
 
-    if (auto ter = removeEmptyHolding(view(), brokerPseudoID, vaultAsset, j_))
+    if (auto ter = removeEmptyHolding(ctx_.getApplyViewContext(), brokerPseudoID, vaultAsset, j_))
         return ter;
 
     auto brokerPseudoSLE = view().peek(keylet::account(brokerPseudoID));
@@ -186,8 +186,6 @@ LoanBrokerDelete::doApply()
 
     view().erase(brokerPseudoSLE);
 
-    view().erase(broker);
-
     {
         auto owner = view().peek(keylet::account(accountID_));
         if (!owner)
@@ -195,9 +193,11 @@ LoanBrokerDelete::doApply()
 
         // Decreases the owner count by two: one for the LoanBroker object, and
         // one for the pseudo-account.
-        adjustOwnerCount(view(), owner, -2, j_);
+        decreaseOwnerCountForObject(view(), owner, broker, 2, j_);
     }
 
+    view().erase(broker);
+
     associateAsset(*broker, vaultAsset);
 
     return tesSUCCESS;

src/libxrpl/tx/transactors/lending/LoanBrokerSet.cpp

@@ -238,9 +238,8 @@ LoanBrokerSet::doApply()
 
         // Increases the owner count by two: one for the LoanBroker object, and
         // one for the pseudo-account.
-        adjustOwnerCount(view, owner, 2, j_);
-        auto const ownerCount = owner->at(sfOwnerCount);
-        if (preFeeBalance_ < view.fees().accountReserve(ownerCount))
+        increaseOwnerCount(view, owner, {}, 2, j_);
+        if (preFeeBalance_ < accountReserve(view, owner, j_))
             return tecINSUFFICIENT_RESERVE;
 
         auto maybePseudo = createPseudoAccount(view, broker->key(), sfLoanBrokerID);
@@ -249,7 +248,8 @@ LoanBrokerSet::doApply()
         auto& pseudo = *maybePseudo;
         auto pseudoId = pseudo->at(sfAccount);
 
-        if (auto ter = addEmptyHolding(view, pseudoId, preFeeBalance_, sleVault->at(sfAsset), j_))
+        if (auto ter = addEmptyHolding(
+                ctx_.getApplyViewContext(), pseudoId, preFeeBalance_, sleVault->at(sfAsset), j_))
             return ter;
 
         // Initialize data fields:

src/libxrpl/tx/transactors/lending/LoanDelete.cpp

@@ -107,9 +107,8 @@ LoanDelete::doApply()
     view.erase(loanSle);
 
     // Decrement the LoanBroker's owner count.
-    // The broker's owner count is solely for the number of outstanding loans,
-    // and is distinct from the broker's pseudo-account's owner count
-    adjustOwnerCount(view, brokerSle, -1, j_);
+    adjustLoanBrokerOwnerCount(view, brokerSle, -1, j_);
+
     // If there are no loans left, then any remaining debt must be forgiven,
     // because there is no other way to pay it back.
     if (brokerSle->at(sfOwnerCount) == 0)
@@ -129,7 +128,7 @@ LoanDelete::doApply()
         }
     }
     // Decrement the borrower's owner count
-    adjustOwnerCount(view, borrowerSle, -1, j_);
+    decreaseOwnerCountForObject(view, borrowerSle, loanSle, 1, j_);
 
     // These associations shouldn't do anything, but do them just to be safe
     associateAsset(*loanSle, vaultAsset);

src/libxrpl/tx/transactors/lending/LoanManage.cpp

@@ -292,6 +292,7 @@ LoanManage::defaultLoan(
         vaultSle->at(sfAccount),
         STAmount{vaultAsset, defaultCovered},
         j,
+        {},
         WaiveTransferFee::Yes);
 }
 

src/libxrpl/tx/transactors/lending/LoanPay.cpp

@@ -625,7 +625,11 @@ LoanPay::doApply()
         {
             // The broker may have deleted their holding. Recreate it if needed
             if (auto const ter = addEmptyHolding(
-                    view, brokerPayee, brokerPayeeSle->at(sfBalance).value().xrp(), asset, j_);
+                    ctx_.getApplyViewContext(),
+                    brokerPayee,
+                    brokerPayeeSle->at(sfBalance).value().xrp(),
+                    asset,
+                    j_);
                 ter && ter != tecDUPLICATE)
             {
                 // ignore tecDUPLICATE. That means the holding already exists,

src/libxrpl/tx/transactors/lending/LoanSet.cpp

@@ -8,6 +8,7 @@
 #include <xrpl/ledger/View.h>
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/LendingHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/ledger/helpers/TokenHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Asset.h>
@@ -56,6 +57,12 @@ LoanSet::preflight(PreflightContext const& ctx)
 
     auto const& tx = ctx.tx;
 
+    if (tx.isFieldPresent(sfSponsorFlags) && isReserveSponsored(tx))
+    {
+        JLOG(ctx.j.debug()) << "LoanSet: reserve sponsorship is not allowed.";
+        return temINVALID_FLAG;
+    }
+
     // Special case for Batch inner transactions
     if (tx.isFlag(tfInnerBatchTxn) && ctx.rules.enabled(featureBatchV1_1) &&
         !tx.isFieldPresent(sfCounterparty))
@@ -512,12 +519,12 @@ LoanSet::doApply()
         }
     }
 
-    adjustOwnerCount(view, borrowerSle, 1, j_);
+    increaseOwnerCount(view, borrowerSle, {}, 1, j_);
+
     {
-        auto const ownerCount = borrowerSle->at(sfOwnerCount);
         auto const balance =
             accountID_ == borrower ? preFeeBalance_ : borrowerSle->at(sfBalance).value().xrp();
-        if (balance < view.fees().accountReserve(ownerCount))
+        if (balance < accountReserve(view, borrowerSle, j_))
             return tecINSUFFICIENT_RESERVE;
     }
 
@@ -531,8 +538,9 @@ LoanSet::doApply()
         borrower == accountID_ || borrower == counterparty,
         "xrpl::LoanSet::doApply",
         "borrower signed transaction");
+    auto applyViewContext = ctx_.getApplyViewContext();
     if (auto const ter = addEmptyHolding(
-            view, borrower, borrowerSle->at(sfBalance).value().xrp(), vaultAsset, j_);
+            applyViewContext, borrower, borrowerSle->at(sfBalance).value().xrp(), vaultAsset, j_);
         ter && ter != tecDUPLICATE)
     {
         // ignore tecDUPLICATE. That means the holding already exists, and
@@ -555,7 +563,11 @@ LoanSet::doApply()
             "broker owner signed transaction");
 
         if (auto const ter = addEmptyHolding(
-                view, brokerOwner, brokerOwnerSle->at(sfBalance).value().xrp(), vaultAsset, j_);
+                applyViewContext,
+                brokerOwner,
+                brokerOwnerSle->at(sfBalance).value().xrp(),
+                vaultAsset,
+                j_);
             ter && ter != tecDUPLICATE)
         {
             // ignore tecDUPLICATE. That means the holding already exists,
@@ -631,9 +643,7 @@ LoanSet::doApply()
 
     // Update the balances in the loan broker
     adjustImpreciseNumber(brokerSle->at(sfDebtTotal), newDebtDelta, vaultAsset, vaultScale);
-    // The broker's owner count is solely for the number of outstanding loans,
-    // and is distinct from the broker's pseudo-account's owner count
-    adjustOwnerCount(view, brokerSle, 1, j_);
+    adjustLoanBrokerOwnerCount(view, brokerSle, 1, j_);
     loanSequenceProxy += 1;
     // The sequence should be extremely unlikely to roll over, but fail if it
     // does

src/libxrpl/tx/transactors/nft/NFTokenAcceptOffer.cpp

@@ -5,6 +5,7 @@
 #include <xrpl/beast/utility/Zero.h>
 #include <xrpl/core/ServiceRegistry.h>
 #include <xrpl/ledger/View.h>
+#include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/NFTokenHelpers.h>
 #include <xrpl/ledger/helpers/TokenHelpers.h>
 #include <xrpl/protocol/Feature.h>
@@ -387,8 +388,7 @@ NFTokenAcceptOffer::transferNFToken(
     auto const buyerOwnerCountAfter = sleBuyer->getFieldU32(sfOwnerCount);
     if (buyerOwnerCountAfter > buyerOwnerCountBefore)
     {
-        if (auto const reserve = view().fees().accountReserve(buyerOwnerCountAfter);
-            buyerBalance < reserve)
+        if (buyerBalance < accountReserve(view(), sleBuyer, j_))
             return tecINSUFFICIENT_RESERVE;
     }
 

src/libxrpl/tx/transactors/nft/NFTokenMint.cpp

@@ -3,6 +3,7 @@
 #include <xrpl/basics/base_uint.h>
 #include <xrpl/beast/utility/instrumentation.h>
 #include <xrpl/ledger/View.h>
+#include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/NFTokenHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Feature.h>
@@ -331,12 +332,14 @@ NFTokenMint::doApply()
     // allows NFTs to be added to the page (and burn fees) without
     // requiring the reserve to be met each time.  The reserve is
     // only managed when a new NFT page or sell offer is added.
-    if (auto const ownerCountAfter =
-            view().read(keylet::account(accountID_))->getFieldU32(sfOwnerCount);
+    auto const sleAccount = view().read(keylet::account(accountID_));
+    if (!sleAccount)
+        return tefINTERNAL;  // LCOV_EXCL_LINE
+
+    if (auto const ownerCountAfter = sleAccount->getFieldU32(sfOwnerCount);
         ownerCountAfter > ownerCountBefore)
     {
-        if (auto const reserve = view().fees().accountReserve(ownerCountAfter);
-            preFeeBalance_ < reserve)
+        if (preFeeBalance_ < accountReserve(view(), sleAccount, j_))
             return tecINSUFFICIENT_RESERVE;
     }
     return tesSUCCESS;

src/libxrpl/tx/transactors/oracle/OracleDelete.cpp

@@ -4,6 +4,7 @@
 #include <xrpl/core/ServiceRegistry.h>
 #include <xrpl/ledger/ApplyView.h>
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
+#include <xrpl/ledger/helpers/OracleHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Indexes.h>
 #include <xrpl/protocol/SField.h>
@@ -13,6 +14,8 @@
 #include <xrpl/protocol/XRPAmount.h>
 #include <xrpl/tx/Transactor.h>
 
+#include <cstdint>
+
 namespace xrpl {
 
 NotTEC
@@ -68,10 +71,8 @@ OracleDelete::deleteOracle(
     if (!sleOwner)
         return tecINTERNAL;  // LCOV_EXCL_LINE
 
-    auto const count = sle->getFieldArray(sfPriceDataSeries).size() > 5 ? -2 : -1;
-
-    adjustOwnerCount(view, sleOwner, count, j);
-
+    std::uint32_t const count = calculateOracleReserve(sle);
+    decreaseOwnerCountForObject(view, sleOwner, sle, count, j);
     view.erase(sle);
 
     return tesSUCCESS;

src/libxrpl/tx/transactors/oracle/OracleSet.cpp

@@ -1,9 +1,11 @@
 #include <xrpl/tx/transactors/oracle/OracleSet.h>
 
 #include <xrpl/basics/chrono.h>
+#include <xrpl/beast/utility/instrumentation.h>
 #include <xrpl/core/ServiceRegistry.h>
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/DirectoryHelpers.h>
+#include <xrpl/ledger/helpers/OracleHelpers.h>
 #include <xrpl/protocol/Feature.h>
 #include <xrpl/protocol/Indexes.h>
 #include <xrpl/protocol/InnerObjectFormats.h>
@@ -22,6 +24,7 @@
 #include <chrono>
 #include <cstddef>
 #include <cstdint>
+#include <cstdlib>
 #include <map>
 #include <memory>
 #include <set>
@@ -150,8 +153,9 @@ OracleSet::preclaim(PreclaimContext const& ctx)
         if (!pairsDel.empty())
             return tecTOKEN_PAIR_NOT_FOUND;
 
-        auto const oldCount = sle->getFieldArray(sfPriceDataSeries).size() > 5 ? 2 : 1;
-        auto const newCount = pairs.size() > 5 ? 2 : 1;
+        auto const oldCount = calculateOracleReserve(sle);
+        auto const newCount = calculateOracleReserve(pairs);
+
         adjustReserve = newCount - oldCount;
     }
     else
@@ -160,7 +164,7 @@ OracleSet::preclaim(PreclaimContext const& ctx)
 
         if (!ctx.tx.isFieldPresent(sfProvider) || !ctx.tx.isFieldPresent(sfAssetClass))
             return temMALFORMED;
-        adjustReserve = pairs.size() > 5 ? 2 : 1;
+        adjustReserve = calculateOracleReserve(pairs);
     }
 
     if (pairs.empty())
@@ -169,7 +173,7 @@ OracleSet::preclaim(PreclaimContext const& ctx)
         return tecARRAY_TOO_LARGE;
 
     auto const reserve =
-        ctx.view.fees().accountReserve(sleSetter->getFieldU32(sfOwnerCount) + adjustReserve);
+        accountReserve(ctx.view, sleSetter, ctx.j, {.ownerCountDelta = adjustReserve});
     auto const& balance = sleSetter->getFieldAmount(sfBalance);
 
     if (balance < reserve)
@@ -179,11 +183,22 @@ OracleSet::preclaim(PreclaimContext const& ctx)
 }
 
 static bool
-adjustOwnerCount(ApplyContext& ctx, int count)
+adjustOracleOwnerCount(ApplyContext& ctx, int count)
 {
+    XRPL_ASSERT(std::abs(count) <= 2, "xrpl::adjustOracleOwnerCount abs(counter) <= 2");
+
     if (auto const sleAccount = ctx.view().peek(keylet::account(ctx.tx[sfAccount])))
     {
-        adjustOwnerCount(ctx.view(), sleAccount, count, ctx.journal);
+        if (count > 0)
+        {
+            increaseOwnerCount(
+                ctx.view(), sleAccount, {}, static_cast<std::uint32_t>(count), ctx.journal);
+        }
+        else if (count < 0)
+        {
+            decreaseOwnerCount(
+                ctx.view(), sleAccount, {}, static_cast<std::uint32_t>(-count), ctx.journal);
+        }
         return true;
     }
 
@@ -228,7 +243,7 @@ OracleSet::doApply()
             priceData.setFieldCurrency(sfQuoteAsset, entry.getFieldCurrency(sfQuoteAsset));
             pairs.emplace(tokenPairKey(entry), std::move(priceData));
         }
-        auto const oldCount = pairs.size() > 5 ? 2 : 1;
+        auto const oldCount = calculateOracleReserve(pairs);
         // update/add/delete pairs
         for (auto const& entry : ctx_.tx.getFieldArray(sfPriceDataSeries))
         {
@@ -266,9 +281,10 @@ OracleSet::doApply()
             (*sle)[sfOracleDocumentID] = ctx_.tx[sfOracleDocumentID];
         }
 
-        auto const newCount = pairs.size() > 5 ? 2 : 1;
-        auto const adjust = newCount - oldCount;
-        if (adjust != 0 && !adjustOwnerCount(ctx_, adjust))
+        auto const newCount = calculateOracleReserve(pairs);
+        int32_t const adjust = newCount - oldCount;
+
+        if (adjust != 0 && !adjustOracleOwnerCount(ctx_, adjust))
             return tefINTERNAL;  // LCOV_EXCL_LINE
 
         ctx_.view().update(sle);
@@ -317,8 +333,8 @@ OracleSet::doApply()
 
         (*sle)[sfOwnerNode] = *page;
 
-        auto const count = series.size() > 5 ? 2 : 1;
-        if (!adjustOwnerCount(ctx_, count))
+        auto const count = calculateOracleReserve(series);
+        if (!adjustOracleOwnerCount(ctx_, count))
             return tefINTERNAL;  // LCOV_EXCL_LINE
 
         ctx_.view().insert(sle);

src/libxrpl/tx/transactors/payment/DepositPreauth.cpp

@@ -7,13 +7,13 @@
 #include <xrpl/ledger/helpers/AccountRootHelpers.h>
 #include <xrpl/ledger/helpers/CredentialHelpers.h>
 #include <xrpl/ledger/helpers/DirectoryHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Feature.h>
 #include <xrpl/protocol/Indexes.h>
 #include <xrpl/protocol/Keylet.h>
 #include <xrpl/protocol/Protocol.h>
 #include <xrpl/protocol/SField.h>
-#include <xrpl/protocol/STAmount.h>
 #include <xrpl/protocol/STArray.h>
 #include <xrpl/protocol/STLedgerEntry.h>
 #include <xrpl/protocol/STTx.h>
@@ -151,6 +151,7 @@ DepositPreauth::preclaim(PreclaimContext const& ctx)
 TER
 DepositPreauth::doApply()
 {
+    auto applyViewContext = ctx_.getApplyViewContext();
     if (ctx_.tx.isFieldPresent(sfAuthorize))
     {
         auto const sleOwner = view().peek(keylet::account(accountID_));
@@ -160,13 +161,10 @@ DepositPreauth::doApply()
         // A preauth counts against the reserve of the issuing account, but we
         // check the starting balance because we want to allow dipping into the
         // reserve to pay fees.
-        {
-            STAmount const reserve{
-                view().fees().accountReserve(sleOwner->getFieldU32(sfOwnerCount) + 1)};
-
-            if (preFeeBalance_ < reserve)
-                return tecINSUFFICIENT_RESERVE;
-        }
+        if (auto const ret = checkReserve(
+                applyViewContext, sleOwner, preFeeBalance_, {.ownerCountDelta = 1}, j_);
+            !isTesSuccess(ret))
+            return ret;
 
         // Preclaim already verified that the Preauth entry does not yet exist.
         // Create and populate the Preauth entry.
@@ -190,7 +188,8 @@ DepositPreauth::doApply()
         slePreauth->setFieldU64(sfOwnerNode, *page);
 
         // If we succeeded, the new entry counts against the creator's reserve.
-        adjustOwnerCount(view(), sleOwner, 1, j_);
+        increaseOwnerCount(applyViewContext, sleOwner, 1, j_);
+        addSponsorToLedgerEntry(applyViewContext, slePreauth);
     }
     else if (ctx_.tx.isFieldPresent(sfUnauthorize))
     {
@@ -207,13 +206,10 @@ DepositPreauth::doApply()
         // A preauth counts against the reserve of the issuing account, but we
         // check the starting balance because we want to allow dipping into the
         // reserve to pay fees.
-        {
-            STAmount const reserve{
-                view().fees().accountReserve(sleOwner->getFieldU32(sfOwnerCount) + 1)};
-
-            if (preFeeBalance_ < reserve)
-                return tecINSUFFICIENT_RESERVE;
-        }
+        if (auto const ret = checkReserve(
+                applyViewContext, sleOwner, preFeeBalance_, {.ownerCountDelta = 1}, j_);
+            !isTesSuccess(ret))
+            return ret;
 
         // Preclaim already verified that the Preauth entry does not yet exist.
         // Create and populate the Preauth entry.
@@ -251,7 +247,8 @@ DepositPreauth::doApply()
         slePreauth->setFieldU64(sfOwnerNode, *page);
 
         // If we succeeded, the new entry counts against the creator's reserve.
-        adjustOwnerCount(view(), sleOwner, 1, j_);
+        increaseOwnerCount(applyViewContext, sleOwner, 1, j_);
+        addSponsorToLedgerEntry(applyViewContext, slePreauth);
     }
     else if (ctx_.tx.isFieldPresent(sfUnauthorizeCredentials))
     {
@@ -289,8 +286,7 @@ DepositPreauth::removeFromLedger(ApplyView& view, uint256 const& preauthIndex, b
     if (!sleOwner)
         return tefINTERNAL;  // LCOV_EXCL_LINE
 
-    adjustOwnerCount(view, sleOwner, -1, j);
-
+    decreaseOwnerCountForObject(view, sleOwner, slePreauth, 1, j);
     // Remove DepositPreauth from ledger.
     view.erase(slePreauth);
 

src/libxrpl/tx/transactors/payment/Payment.cpp

@@ -10,6 +10,7 @@
 #include <xrpl/ledger/helpers/CredentialHelpers.h>
 #include <xrpl/ledger/helpers/MPTokenHelpers.h>
 #include <xrpl/ledger/helpers/PermissionedDEXHelpers.h>
+#include <xrpl/ledger/helpers/SponsorHelpers.h>
 #include <xrpl/ledger/helpers/TokenHelpers.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Asset.h>
@@ -37,6 +38,7 @@
 
 #include <algorithm>
 #include <cstdint>
+#include <limits>
 #include <memory>
 #include <optional>
 #include <unordered_set>
@@ -120,6 +122,21 @@ Payment::preflight(PreflightContext const& ctx)
     if (!ctx.rules.enabled(featureMPTokensV1) && isDstMPT)
         return temDISABLED;
 
+    if (tx.isFlag(tfSponsorCreatedAccount))
+    {
+        if (!ctx.rules.enabled(featureSponsor))
+            return temDISABLED;
+
+        if (tx.isFlag(tfNoRippleDirect) || tx.isFlag(tfPartialPayment) || tx.isFlag(tfLimitQuality))
+            return temINVALID_FLAG;
+
+        if (tx.isFieldPresent(sfSendMax) || tx.isFieldPresent(sfPaths))
+            return temINVALID;
+
+        if (!dstAmount.native())
+            return temBAD_AMOUNT;
+    }
+
     if (!mpTokensV2 && isDstMPT && ctx.tx.isFieldPresent(sfPaths))
         return temMALFORMED;
 
@@ -383,15 +400,28 @@ Payment::preclaim(PreclaimContext const& ctx)
         {
             // accountReserve is the minimum amount that an account can have.
             // Reserve is not scaled by load.
-            JLOG(ctx.j.trace()) << "Delay transaction: Destination account does not exist. "
-                                << "Insufficent payment to create account.";
+            if (!ctx.tx.isFlag(tfSponsorCreatedAccount))
+            {
+                // The minimum amount when creating a Sponsored Account is 1 drop.
+                // Since the reserve is covered by the sponsor, you don't need to hold the
+                // 1-increment reserve yourself.
+                JLOG(ctx.j.trace()) << "Delay transaction: Destination account does not exist. "
+                                    << "Insufficient payment to create account.";
 
-            // TODO: de-dupe
-            // Another transaction could create the account and then this
-            // transaction would succeed.
-            return tecNO_DST_INSUF_XRP;
+                // TODO: de-dupe
+                // Another transaction could create the account and then this
+                // transaction would succeed.
+                return tecNO_DST_INSUF_XRP;
+            }
         }
     }
+    else if (ctx.tx.isFlag(tfSponsorCreatedAccount))
+    {
+        // The tfSponsorCreatedAccount flag is specific to account creation via
+        // sponsorship. If the destination account already exists, applying this
+        // flag is invalid.
+        return tecNO_SPONSOR_PERMISSION;
+    }
     else if (sleDst->isFlag(lsfRequireDestTag) && !ctx.tx.isFieldPresent(sfDestinationTag))
     {
         // The tag is basically account-specific information we don't
@@ -470,6 +500,27 @@ Payment::doApply()
         sleDst->setFieldU32(sfSequence, view().seq());
         sleDst->setFieldAmount(sfBalance, XRPAmount(beast::kZero));
 
+        if (ctx_.tx.isFlag(tfSponsorCreatedAccount))
+        {
+            auto const sponsor = view().peek(keylet::account(accountID_));
+            if (!sponsor)
+                return tefINTERNAL;  // LCOV_EXCL_LINE
+            auto const currentSponsoringAccountCount =
+                sponsor->getFieldU32(sfSponsoringAccountCount);
+            if (currentSponsoringAccountCount == std::numeric_limits<std::uint32_t>::max())
+            {
+                // LCOV_EXCL_START
+                JLOG(j_.fatal()) << "Sponsoring account count overflow for account "
+                                 << to_string(accountID_);
+                return tecINTERNAL;
+                // LCOV_EXCL_STOP
+            }
+            sponsor->setFieldU32(sfSponsoringAccountCount, currentSponsoringAccountCount + 1);
+
+            addSponsorToLedgerEntry(sleDst, sponsor);
+            view().update(sponsor);
+        }
+
         view().insert(sleDst);
     }
     else
@@ -636,16 +687,12 @@ Payment::doApply()
     if (!sleSrc)
         return tefINTERNAL;  // LCOV_EXCL_LINE
 
-    // ownerCount is the number of entries in this ledger for this
-    // account that require a reserve.
-    auto const ownerCount = sleSrc->getFieldU32(sfOwnerCount);
+    // the number of reserves in this ledger for this account that require a
+    // reserve.
+    auto const reserve = accountReserve(view(), sleSrc, j_);
 
-    // This is the total reserve in drops.
-    auto const reserve = view().fees().accountReserve(ownerCount);
-
-    // In a delegated payment, the fee payer is the delegated account,
-    // not the source account (accountID_).
-    bool const accountIsPayer = (ctx_.tx.getFeePayer() == accountID_);
+    // In a delegated / fee sponsored payment, the fee payer is not the source account (accountID_).
+    bool const accountIsPayer = ctx_.tx.getFeePayerID() == accountID_;
 
     // preFeeBalance_ is the balance on the source account (accountID_) BEFORE the fees
     // were charged. If source account is the fee payer, it must also cover the fee.