test(behaviour): fork branch create fails with 409 empty repository

[guyoron1]

Upstream: fullsend-ai/issues/5671

What happens

Parallel behaviour scenarios that use Given a fork sometimes fail while creating the fork head branch with:

creating fork branch: get ref for default branch: github api: 409 Git Repository is empty.

Observed on PR fullsend-ai#5407 behaviour runs (e.g. https://github.com/fullsend-ai/fullsend/actions/runs/30354560530), scenario Fork PR sync + label dispatches harness. Sibling fork scenarios in the same suite can still pass.

CreateFork / CreateForkInOrg has returned, but the fork’s default-branch ref is not readable yet.

What should happen

After a fork is created (or reused), behaviour steps that need the default branch (e.g. create branch, commit) should only proceed once the fork has a usable default-branch ref. Transient empty-repo races should not fail the scenario.

How to reproduce

1. Run the behaviour suite with parallel godog concurrency (CI default).
2. Include fork-dispatch scenarios (features/dispatch/fork-dispatch.feature).
3. Intermittently: fork create succeeds, then immediate CreateBranch / get default-branch ref returns 409 Git Repository is empty.

Context

Follow-up from behaviour flakes on fullsend-ai#5407. Distinct from URL-dispatch product failures; this is fork readiness under parallel load. No dedicated open issue found for this error string in behaviour tests.

Related: fork lifecycle docs in docs/guides/dev/behaviour-testing.md (ephemeral per-lease forks).

[guyoron1]

/fs-triage

[fullsend-ai-triage]

🤖 Finished Triage · ✅ Success · Started 10:41 AM UTC · Completed 10:45 AM UTC
Commit: 9394865 · View workflow run →

[fullsend-ai-triage]

Triage Summary

Severity: Medium · Category: Bug (test infrastructure)

Problem

The Given a fork behaviour test step calls CreateFork and returns immediately, but GitHub's fork API is asynchronous — it responds before Git data replication completes. Under parallel godog concurrency, the subsequent CreateBranch step hits a 409 Git Repository is empty error when the fork's default-branch ref is not yet readable.

Root Cause Hypothesis

givenFork() lacks a readiness poll after CreateFork returns. The same class of async-readiness race already has a fix in the codebase — awaitWorkflowReady in RepoEnsurer uses the same poll-until-ready pattern.

Recommended Fix

Add a readiness poll after CreateFork returns, following the existing awaitWorkflowReady pattern:

// Poll until the fork's default branch is readable.
for attempt := 0; attempt < 30; attempt++ {
    _, err := w.SCM.GetDefaultBranch(ctx, forkOwner, forkRepo)
    if err == nil {
        break
    }
    time.Sleep(2 * time.Second)
}

Proposed Test

// TestGivenFork_PollsForDefaultBranch
// Setup: FakeClient where CreateForkInOrg succeeds but GetDefaultBranch
//   returns 409 for first N calls, then succeeds
// Assert: givenFork returns nil after retries
// Edge: retries exhausted → clear timeout error wrapping last 409
// Edge: immediate success → no sleep, returns immediately

Upstream tracking: fullsend-ai#5671 (triaged, ready-to-code).

---

Labels: This is a confirmed test infrastructure bug (race condition). type/bug and ready-to-code apply since the fix is well-understood with an established pattern to follow.

[fullsend-ai-coder]

🤖 Code · ❌ Terminated · Started 10:46 AM UTC · Ended 11:08 AM UTC
Commit: 9394865 · View workflow run →

[guyoron1]

/fs-code

[fullsend-ai-coder]

🤖 Finished Code · ✅ Success · Started 10:46 AM UTC · Completed 11:08 AM UTC
Commit: 9394865 · View workflow run →

[fullsend-ai-coder]

🤖 Finished Code · ✅ Success · Started 11:13 AM UTC · Completed 11:17 AM UTC
Commit: 9394865 · View workflow run →

[fullsend-ai-coder]

An open PR already addresses this issue — skipping automated implementation.

• fix(#697): add fork readiness polling to forge layer #720 by @app/fullsend-ai-coder

To override, comment /fs-code --force on this issue.

_{Posted by fullsend pre-code check}