[ANCHOR-1242]: Contract sub invocation transfers are skipped

[amandagonsalves]

Description

Follow-up: credit Variant B instead of skipping it. The first pass logged an errorF and skipped when no matching operation was found. The Soroban transfer event's 4th topic is already the SEP-11 asset string - shouldProcess() already decodes it into ShouldProcessResult.sep11Asset, unused. org.stellar.sdk.Asset.create(String) parses that exact format back into an Asset, then .toXdr() - the same method SacToAssetMapper.getAssetFromSac itself already uses for the same conversion, just from a different source string.

Changes

• StellarRpcPaymentObserver.processTransferEvent: replaced txn.getOperations().get(operationIndex) with a TOID-based identity lookup - derives wantedOpId from new TOID(sequenceNumber, applicationOrder, operationIndex + 1).toInt64(), then stream-filters txn.getOperations() by getOperationId(o).equals(wantedOpId). Adds import org.stellar.sdk.TOID.
• StellarRpcPaymentObserver.getOperationId: new private helper that extracts the id field from whichever sub-operation (paymentOperation, pathPaymentOperation, or invokeHostFunctionOperation) is set on a LedgerOperation.
• StellarRpcPaymentObserver.buildSubInvocationOperation: new private helper - when the TOID lookup finds no match, builds a synthetic LedgerInvokeHostFunctionOperation directly from the transfer event's already-decoded fromAddr/toAddr/amount/sep11Asset fields. processTransferEvent replaces txn's (filtered-empty) operations list with this single synthetic operation and falls through to processOperation unchanged, so the synthetic payment flows through the exact same SEP-6/24/31 matching and crediting pipeline as any other payment. Logs infoF on success; only logs errorF/skips if the event's asset string can't be parsed at all (not expected for a protocol-compliant event).
• StellarRpcPaymentObserver.processOperation: guarded the INVOKE_HOST_FUNCTION case's SAC lookup (if (invokeOp.getAsset(false) == null)) so it doesn't discard the asset already resolved from the event, mirroring the guard DefaultPaymentListener.validate() already uses for the same call.
• StellarRpcPaymentObserverTest: rewrote the sub-invocation "skip" test into a "credit" test (asserts handleEvent is called with the correct from/to/amount/operationId); added a new test for the genuine give-up path (malformed event asset string → skipped, no throw).
• StellarRpcObserverIndexDomainTest: updated the dedicated sub-invocation test and the mixed-batch test to assert crediting instead of skipping.

Acceptance Criteria

• A two-operation transaction [MANAGE_DATA, PAYMENT→dist] with transfer event at operationIndex=1 is credited with the correct from/to/amount/operationId.
• A transfer event whose corresponding full-list operation is absent from the compacted list (contract sub-invocation) is credited via a synthetic operation built from the event's own fields, with the correct from/to/amount/operationId.
• A transfer event with an unparseable asset string is skipped without throwing, and the observer stays RUNNING.
• A mixed batch containing a normal single-op, a multi-op, and a sub-invocation event processes all three without crashing, crediting all three.
• Observer status remains RUNNING after any of the above scenarios.
• Existing StellarRpcPaymentObserverTest and StellarRpcObserverPoisonResilienceTest tests continue to pass unchanged.
• Horizon mode (HorizonPaymentObserver) is unaffected.

Context

#3791580

Testing

• Unit: ./gradlew :platform:test --tests "org.stellar.anchor.platform.observer.stellar.StellarRpcPaymentObserverTest"
• Integration: ./gradlew :platform:test --tests "org.stellar.anchor.platform.observer.stellar.StellarRpcObserverIndexDomainTest"

Documentation

N/A

Known limitations

N/A