rabbit hole: refactor dirAdd to find gaps in "full" directories.

- This would potentially be very expensive to implement, so don't.
- However, it might be a good start for a ledger fix option.

include/xrpl/ledger/helpers/NFTokenHelpers.h

@@ -20,6 +20,10 @@ removeTokenOffersWithLimit(
     Keylet const& directory,
     std::size_t maxDeletableOffers);
 
+/** Returns tesSUCCESS if NFToken has few enough offers that it can be burned */
+TER
+notTooManyOffers(ReadView const& view, uint256 const& nftokenID);
+
 /** Finds the specified token in the owner's token directory. */
 std::optional<STObject>
 findToken(ReadView const& view, AccountID const& owner, uint256 const& nftokenID);

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(DefragDirectories,          Supported::no,  VoteBehavior::DefaultNo)
 XRPL_FEATURE(MPTokensV2,                  Supported::no, VoteBehavior::DefaultNo)
 XRPL_FIX    (Security3_1_3,               Supported::no, VoteBehavior::DefaultNo)
 XRPL_FIX    (PermissionedDomainInvariant, Supported::yes, VoteBehavior::DefaultNo)