fix(consensus): preserve export state without rng

src/xrpld/app/consensus/ConsensusExtensionsDesign.md

@@ -192,6 +192,11 @@ Export sig convergence runs in parallel with RNG. An export-side convergence
 failure must not change RNG semantics; an RNG fallback must not make export
 unsafe. Each feature has its own gate and fallback.
 
+Accept-time cleanup must preserve Export state through `buildLCL` whenever
+`featureExport` is enabled. RNG-disabled does not mean extensions-disabled:
+`ttEXPORT` still needs the round's export sidecar convergence state when it
+applies.
+
 CSF consensus tests model the export sidecar gate directly. Testnet scenarios
 under `.testnet/scenarios/export/` cover live-node Export+CE behavior and the
 Export-only unanimity mode.

src/xrpld/app/consensus/RCLConsensus.cpp

@@ -587,13 +587,14 @@ RCLConsensus::Adaptor::doAccept(
     }
 
     //@@start auxiliary-pre-build-injection
-    // Inject consensus entropy pseudo-transaction (if amendment enabled)
-    // This must happen before buildLCL so the entropy tx is in the ledger
+    // Inject consensus entropy pseudo-transaction (if amendment enabled).
+    // Export-only rounds still need extension state preserved through buildLCL
+    // so ttEXPORT can observe exportSigSetHash convergence at apply time.
     //@@start accept-time-cleanup-disabled
-    if (prevLedger.ledger_->rules().enabled(featureConsensusEntropy))
+    if (ce().rngEnabled())
         ce().onPreBuild(retriableTxs, prevLedger.seq() + 1);
-    else
-        ce().clearRngState();  // CE disabled — clear extension state now
+    else if (!ce().exportEnabled())
+        ce().clearRngState();
     //@@end accept-time-cleanup-disabled
 
     auto built = buildLCL(