chancloser: stabilize remote RBF coop tests

[starius]

Change Description

CI started panicking in TestRbfChannelFlushingTransitions/early_offer / TestRbfCloseClosingNegotiationRemote (see GitHub Actions run https://github.com/lightningnetwork/lnd/actions/runs/19155841408/job/54756127218?pr=10352) because the cached remote offer could fire before the test harness registered its mock CloseSigner expectations. When that happened, the mock complained that CreateCloseProposal was unexpected:

panic:
assert: mock: I don't know what to return because the method call was unexpected.

Fix this by letting assertSingleRemoteRbfIteration take a trigger callback. Tests that rely on asynchronously replayed offers now install their expectations first and then fire the event via the callback. All other call sites pass nil, preserving their existing behavior.

Steps to Test

Reproduction (on master)

1. Modify lnwallet/chancloser/rbf_coop_test.go

• Add time.Sleep(10 * time.Millisecond) before the first call of closeHarness.assertSingleRemoteRbfIteration (in function TestRbfChannelFlushingTransitions).

3. go test ./lnwallet/chancloser -run TestRbfChannelFlushingTransitions/early_offer

4. The panic reproduces immediately.

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.

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• The change is not insubstantial. Typo fixes are not accepted to fight bot spam.
• 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.
• There is a change description in the release notes, or [skip ci] in the commit message for small changes.

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[lightninglabs-deploy]

@yyforyongyu: review reminder
@ziggie1984: review reminder

[ziggie1984]

/gemini review

[gemini-code-assist]

Code Review

This pull request addresses a race condition in the remote RBF cooperation tests by introducing a trigger callback to the assertSingleRemoteRbfIteration test helper. This change ensures that mock expectations are set up before the test event is fired, preventing panics in CI. The implementation is clean and effectively solves the issue while maintaining backward compatibility for existing call sites. I have one suggestion to improve documentation in line with the project's style guide.

[gemini-code-assist]

The signature of this function has been modified, but it lacks a comment explaining its purpose and the new trigger parameter. According to the repository's style guide, all functions should be commented to improve readability and maintainability.

Suggested change

	func (r *rbfCloserTestHarness) assertSingleRemoteRbfIteration(
	initEvent *OfferReceivedEvent, balanceAfterClose,
	absoluteFee btcutil.Amount, sequence uint32, iteration bool,
	sendInit bool) {
	trigger func()) {
	// assertSingleRemoteRbfIteration asserts that a single RBF iteration initiated
	// by the remote party completes successfully. The trigger function can be used
	// to control when the event that kicks off the process is sent, which is
	// useful for tests that need to set up mocks before the event is processed.
	// If trigger is nil, the initEvent is sent directly.
	func (r *rbfCloserTestHarness) assertSingleRemoteRbfIteration(
	initEvent *OfferReceivedEvent, balanceAfterClose,
	absoluteFee btcutil.Amount, sequence uint32, iteration bool,
	trigger func()) {

References

1. The style guide (lines 17-20) requires every function to be commented with its purpose and assumptions. The comment must start with the function name and be a complete sentence. ^(link)

[starius]

Fixed