contractcourt: retain deadline across contest resolution

[ziggie1984]

Change Description

Outgoing contest resolvers embed the timeout resolver they transition to once
the outgoing HTLC reaches its expiry. Forward the corresponding incoming HTLC
expiry to that embedded resolver so the existing deadline remains available
after the transition.

The added test exercises the contest-to-timeout transition and checks that the
supplied deadline is retained.

Steps to Test

go test ./contractcourt \
  -run 'TestHtlcOutgoingResolver(SupplementDeadline|Timeout|RemoteClaim)$' \
  -count=1

Pull Request Checklist

Testing

• Your PR passes all CI checks.
• Tests covering the changed behavior are included.

Code Style and Documentation

• The change follows the code documentation and line-length guidelines.
• Commits follow the ideal Git commit structure.
• A change description is included in the 0.21.2 release notes.

[github-actions]

🔴 PR Severity: CRITICAL

gh pr view | 3 files | 47 lines changed

🔴 Critical (1 file)

• contractcourt/htlc_outgoing_contest_resolver.go - on-chain HTLC dispute/breach resolution logic (contractcourt/*)

🟢 Low (2 files)

• contractcourt/htlc_outgoing_contest_resolver_test.go - test-only change
• docs/release-notes/release-notes-0.21.2.md - release notes

Analysis

This PR modifies contractcourt/htlc_outgoing_contest_resolver.go, which is part of the on-chain contract dispute/breach resolution code path (contractcourt/*). Per policy, any change to this package is classified CRITICAL regardless of size, since bugs here can affect fund safety during channel breaches. The change itself is small (6 lines added/2 removed in the non-test file, plus accompanying tests and release notes), so no severity bump was needed beyond the base CRITICAL classification — but the change still warrants expert review given the sensitivity of this code path.

---

_{To override, add a severity-override-{critical,high,medium,low} label.}

[Roasbeef]

LGTM 🌞

[yyforyongyu]

LGTM

[github-actions]

Created backport PR for v0.20.x-branch:

• [v0.20.x-branch] Backport #11032: contractcourt: retain deadline across contest resolution #11033 with remaining conflicts!

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin backport-11032-to-v0.20.x-branch
git worktree add --checkout .worktree/backport-11032-to-v0.20.x-branch backport-11032-to-v0.20.x-branch
cd .worktree/backport-11032-to-v0.20.x-branch
git reset --hard HEAD^
git cherry-pick -x 5b4c5067dbd3aa0714b8550511b1e05f25220b83
git push --force-with-lease

[github-actions]

Successfully created backport PR for v0.21.x-branch:

• [v0.21.x-branch] Backport #11032: contractcourt: retain deadline across contest resolution #11034