node: track reannounced mempool transactions in unbroadcast set #36090

Problem

When BroadcastTransaction is invoked with TxBroadcast::MEMPOOL_AND_BROADCAST_TO_ALL (via send, sendtoaddress, or sendrawtransaction) for a transaction that is already admitted to the mempool (for example, loaded from mempool.dat on node startup/restart, or resubmitted by wallet/RPC), it previously skipped tracking the transaction in m_unbroadcast_txids.

If initial P2P broadcast attempts failed because outbound peers had not yet established connections during node restart, the transaction was never retried via ReattemptInitialBroadcast(), leaving locally submitted wallet/RPC transactions in an unbroadcast state indefinitely even while appearing as InMempool.

Solution

In src/node/transaction.cpp:

• When mempool->get(txid) succeeds during BroadcastTransaction, if broadcast_method == TxBroadcast::MEMPOOL_AND_BROADCAST_TO_ALL, call node.mempool->AddUnbroadcastTx(txid).

Testing

• Added deterministic functional test test/functional/wallet_restart_mempool_unbroadcast.py reproducing the exact startup race with persisted mempool and verifying transaction delivery upon subsequent peer connection.
• Updated test/functional/mempool_unbroadcast.py to assert that rebroadcasting an existing transaction tracks it in the unbroadcast set until delivered to peers.
• Ran all 819 unit test cases (test_bitcoin) and relevant functional tests (mempool_unbroadcast.py, wallet_restart_mempool_unbroadcast.py, mempool_persist.py, wallet_resendwallettransactions.py, mempool_packages.py, mempool_accept_wtxid.py).

Fixes #35589.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/36090.

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Thx, but LLM output is not accepted if the author can not properly explain, test or could have written the change themselves. Also, LLM generated content is not allowed in comments/communications. See https://github.com/bitcoin/bitcoin/blob/master/doc/AI_POLICY.md

The bottleneck in this project has always been review and testing, not writing code. Development here is intentionally conservative and slow, and reviewer attention is the scarcest resource we have. LLMs have made this worse, anyone can now prompt them and post their output as PRs. There is an infinite amount plausible looking "improvements" for LLMs to suggest and work on.

Unless we fully trust LLMs to both write and review code, humans still have to spend time understanding the proposed changes, which incurs a non-zero cost for every opened PR.

I understand that contributing to this project can be intimidating, and using LLMs may seem tempting, but it really creates more issues for this project than it solves. The best way to help this project, is to review and test changes. You can use LLMs for this, but you shouldn't solely rely on them, or just post their output.

I am asking you to reconsider whether it's something you genuinely think the project should pursue, independent of what your LLM suggested.

See https://github.com/bitcoin/bitcoin/blob/master/doc/AI_POLICY.md

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