Filter pending deposits by HeadId in all head-level handlers
The following handlers were passing unfiltered pendingDeposits, causing
them to potentially pick deposits from other heads:
1. ReqTx handler (line 1739): Could select wrong deposit for ReqSn,
causing RequestedDepositNotFoundLocally errors on peers.
2. OnDecrementTx handler (line 1666): Could include wrong deposit in
subsequent ReqSn via setExistingDeposit.
3. Rollback handler (line 1707): maybeRepostIncrementTx could find
and repost for wrong head's deposit.
Other handlers (ReqSn, AckSn, onOpenChainTick) already correctly used
depositsForHead to filter deposits by the current head's ID.
Note: onChainTick intentionally processes ALL deposits as it handles
node-level deposit status tracking (DepositActivated/DepositExpired),
not head-specific logic.
Co-Authored-By: Claude Opus 4.5 <[email protected]>