itest: tolerate deferred HTLC timeout sweeps

[yyforyongyu]

Change Description

The local-claim outgoing HTLC itest assumed Bob's mature timeout sweep is in the mempool immediately after the force-close block is processed. In practice, the resolver can offer the mature input after the sweeper has already processed that block, so publication can wait for the next blockbeat.

This PR updates the itest to accept both valid scheduler outcomes. If the sweep is not in the mempool yet, the test mines an empty block to trigger the next sweep round, then confirms the sweep. No production sweeper or resolver behavior changes are included.

Steps to Test

• GOWORK=off make fmt
• git diff --check 2a4aab892a8aa48ebdf103726562080f029b7884..HEAD
• GOWORK=off make itest backend=bitcoind dbbackend=postgres nativesql=1 icase=multihop-local_claim_outgoing_htlc_simple_taproot_zero_conf
• GOWORK=off make lint

Pull Request Checklist

Testing

• Your PR passes all CI checks.
• Tests covering the positive and negative (error paths) are included.
• Bug fixes contain tests triggering the bug to prevent regressions.

Code Style and Documentation

• The change is not insubstantial.
• The change obeys the Code Documentation and Commenting guidelines, and lines wrap at 80.
• Commits follow the Ideal Git Commit Structure.
• Any new logging statements use an appropriate subsystem and logging level.
• Any new lncli commands have appropriate tags in the comments for the rpc in the proto file.
• No release note is included because this is an itest-only flake fix.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a timing issue where outgoing HTLC timeout resolvers might delay publication of sweep inputs until the next block, even when the input is already mature. By setting the 'Immediate' flag in the sweep parameters, the system ensures these deadline-sensitive transactions are published immediately upon being offered to the sweeper.

Highlights

• Immediate HTLC Timeout Sweeps: Updated HTLC timeout resolvers to mark sweep inputs as 'Immediate', ensuring they are published as soon as they are offered, even if the sweeper has already processed the maturity block.
• Test Suite Enhancement: Updated the mock sweeper and test cases to verify that HTLC timeout sweeps are correctly configured with the 'Immediate' flag.

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[gemini-code-assist]

Code Review

This pull request updates the HTLC timeout resolver to sweep inputs immediately by setting the Immediate parameter to true for both timeout transactions and direct HTLC outputs. It also updates the mock sweeper and unit tests to verify this behavior. The review feedback suggests improving code formatting by adding spacing between case stanzas in a select block in the tests, and adding a comment explaining the reasoning behind setting Immediate: true for direct HTLC outputs to ensure consistency and maintainability.

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[github-actions]

🔴 PR Severity: CRITICAL

Automated classification | 2 files (excl. tests) | 15 lines changed (excl. tests)

🔴 Critical (1 file)

• contractcourt/htlc_timeout_resolver.go - On-chain HTLC timeout dispute resolution logic (contractcourt/*)

🟢 Low (1 file)

• docs/release-notes/release-notes-0.22.0.md - Release notes documentation

⬜ Excluded from severity count (2 files)

• contractcourt/commit_sweep_resolver_test.go - test file
• contractcourt/htlc_timeout_resolver_test.go - test file

Analysis

This PR modifies contractcourt/htlc_timeout_resolver.go, which is part of the contractcourt package responsible for on-chain dispute resolution and HTLC timeout handling. Changes here directly affect the state machine that resolves HTLCs on-chain when a channel is force-closed — incorrect behavior could result in loss of funds if timeout outputs are not swept correctly before expiry.

The change is small (7 additions, 2 deletions in the production file), but the contractcourt package warrants expert review given its role in fund safety. The accompanying test additions cover the modified behavior.

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