fix(export): deduplicate export sigs across proposals within a round

src/xrpld/app/consensus/RCLConsensus.cpp

@@ -313,6 +313,7 @@ RCLConsensus::Adaptor::propose(RCLCxPeerPos::Proposal const& proposal)
     //@@start export-sig-attachment
     // Attach export signatures for any ttEXPORT txns in the current set.
     // Each "signature" is: txnHash (32 bytes) + validator pubkey (33 bytes).
+    // Only attach once per export per round (markSent deduplicates).
     // XAHAUD_NO_EXPORT_SIG=1 disables sig attachment (for testing sub-quorum).
     if (auto const* noSig = std::getenv("XAHAUD_NO_EXPORT_SIG");
         noSig && std::string(noSig) == "1")
@@ -329,6 +330,11 @@ RCLConsensus::Adaptor::propose(RCLCxPeerPos::Proposal const& proposal)
                 if (stx && stx->getTxnType() == ttEXPORT)
                 {
                     auto const txHash = stx->getTransactionID();
+
+                    // Only attach our sig on the first proposal this round.
+                    if (!exportSigCollector().markSent(txHash))
+                        continue;
+
                     Serializer s;
                     s.addBitString(txHash);
                     s.addRaw(validatorKeys_.keys->publicKey.slice());
@@ -1668,6 +1674,7 @@ RCLConsensus::Adaptor::validatorKey() const
 void
 RCLConsensus::Adaptor::clearRngState()
 {
+    exportSigCollector().clearRound();
     pendingCommits_.clear();
     pendingReveals_.clear();
     nodeIdToKey_.clear();

src/xrpld/app/misc/ExportSigCollector.h

@@ -8,13 +8,16 @@
 
 namespace ripple {
 
-/// Minimal export signature collector for the retriable export approach.
-/// Tracks which validators have "signed" each pending export.
+/// Export signature collector for the retriable export approach.
+/// Tracks which validators have "signed" each pending export, and
+/// which exports we've already attached our own sig to (so we don't
+/// redundantly re-send on every proposal).
 /// Thread-safe.
 class ExportSigCollector
 {
     mutable std::mutex mutex_;
     std::unordered_map<uint256, std::set<PublicKey>> sigs_;
+    std::set<uint256> sentThisRound_;
 
 public:
     void
@@ -46,10 +49,26 @@ public:
         std::lock_guard lock(mutex_);
         sigs_.erase(txnHash);
     }
+
+    /// Returns true if we haven't sent our sig for this tx yet this round.
+    /// Marks it as sent on first call.
+    bool
+    markSent(uint256 const& txnHash)
+    {
+        std::lock_guard lock(mutex_);
+        return sentThisRound_.insert(txnHash).second;
+    }
+
+    /// Clear per-round state. Call at the start of each consensus round.
+    void
+    clearRound()
+    {
+        std::lock_guard lock(mutex_);
+        sentThisRound_.clear();
+    }
 };
 
-/// Global instance for the prototype.
-/// In production this would be owned by Application.
+/// Global instance. In production this would be owned by Application.
 inline ExportSigCollector&
 exportSigCollector()
 {