#35893 test: cover submitpackage other-wtxid for same-txid-diff-witness

• Add functional test coverage for submitpackage response formatting
• Protects against regressions when a package transaction shares a txid with a mempool entry

This PR adds a functional test case to test/functional/rpc_packages.py verifying that submitpackage returns other-wtxid when attempting to submit a transaction whose txid matches an existing mempool transaction with a different witness.

Problem: While the underlying mempool behavior had unit test coverage, the RPC layer's JSON response structure for this scenario was not covered by any functional test.

P3 · test coverage

• P3 because it pins documented JSON response formats for package submissions
• Ensures RPC clients do not encounter silent compatibility regressions

Pins documented RPC response structure for package submission under same-txid-different-witness conditions, ensuring JSON compatibility does not regress.

Membership: Touches test/functional/rpc_packages.py to test the JSON-RPC response format of submitpackage.

Factors: security/stability 0, bug 0, performance 0, user value 1, leverage 0

• Ready for review, small patch with passing CI

The patch is small, CI is passing, and the only reviewer suggestion has been addressed and re-ACKed.

Author status: active

Resolved concerns:

• jeanpablojp noted an unnecessary parent transaction generation step, which the author removed in a force push.

• Positive sentiment with no outstanding concerns
• Concept approval without stated reasons (instagibbs)
• Verified by testing after addressing cleanup feedback (jeanpablojp)

Concept ACK and tested ACK with no outstanding objections.

The PR has received positive engagement from two contributors with no dissent.

• instagibbs gave a concept ACK.
• jeanpablojp tested the PR and re-ACKed after the author removed an unnecessary step.

Review verdicts (DrahtBot): 1

• ACK: jeanpablojp

31 lines under test/bench/ci.

• test/functional/rpc_packages.py +31/-0

This pull request adds functional test coverage in rpc_packages.py for submitpackage when encountering a same-txid-different-witness transaction. It ensures the JSON response properly surfaces the other-wtxid field matching the transaction already in the mempool. Review is straightforward and in a clean state, with a concept ACK and a tested re-ACK following a minor cleanup.