[ceciliaromao]

Description

• LedgerClientHelper.parseOperationAndSourceAccountAndMemo now accepts a transaction whose source is a muxed account (M..., CAP-0027), both for a V1 envelope and for the inner transaction of a fee bump. The source is resolved by a new resolveTransactionSource helper that switches on the MuxedAccount discriminant and returns the base G... address, the same shape resolveSourceAccount already returns for an operation source.
• Before, the parser read the source with getEd25519() only, which is null for a muxed source, so it threw a NullPointerException. That exception is not a LedgerDecodeException, so it escaped Horizon.getTransaction and StellarRpc.fromGetTransactionResponse.
• A source whose key type is neither ed25519 nor muxed ed25519 makes the parser log and return null, like its other unparseable-envelope cases. The XDR union has no other arm, so this only completes the switch.

Context

• HackerOne report 4018874
• A transaction from a muxed source made the ledger parser throw, which put the payment observer in PUBLISHER_ERROR on the same operation and made notify_onchain_funds_received / notify_onchain_funds_sent fail for that transaction. This is the fix for a reported security finding.
• Wrapping the exception in LedgerDecodeException was ruled out: that path skips the operation and advances the cursor, which would silently drop a legitimate payment. The parser has to support the muxed arm instead.
• The source is reduced to the G... address because that is what the rest of the platform expects (from_account is a G... everywhere, and Horizon reports source_account the same way). Nothing reads the source's muxed id.
• The muxed destination byte order in convert() is a different bug and is not part of this change.

Testing

• ./gradlew test
• ./gradlew :core:test --tests "org.stellar.anchor.ledger.LedgerClientHelperTest": 6 new tests. A muxed V1 source and a muxed fee-bump inner source parse to the base G..., for muxed ids 0, 1 and 2^64-1. A payment without an operation source is attributed to the base G..., and a payment with its own operation source keeps it. An unknown key type returns null without throwing. The existing ed25519 V0, V1 and fee-bump tests are the controls.
• ./gradlew :core:test --tests "org.stellar.anchor.ledger.MuxedTransactionSourceTest": 5 new tests that run a real muxed-source payment through Horizon.getTransaction (V1 and fee bump), StellarRpc.fromGetTransactionResponse (V1 and fee bump) and waitForTransactionAvailable.
• All 11 new tests fail with the NullPointerException on develop and pass with this change.

Documentation

N/A: no documentation change, this is a bug fix.

Known limitations

• The source's muxed id is not carried into LedgerTransaction.sourceAccount; only the base G... is kept.
• The observers and Platform API handlers are not tested directly: their tests mock getTransaction, so the fix is covered one layer below, in the real Horizon and RPC parse paths.