fix(oauth): follower last-chance read after poll deadline

[waleedlatif1]

Summary

• Addresses the cursor-bot follow-up on improvement(oauth): coalesce token refresh + cache terminal failures #4706: when a coalesced refresh leader takes longer than the follower's 3s poll window, the follower returned null even if the leader persisted moments later. Adds a single last-chance DB read after the poll loop so a just-finished leader is still caught.
• Trade-off: 1 extra DB read only in the rare timeout case. No-op in the common path.

Type of Change

• Bug fix

Testing

• New unit test: follower does a final read after timeout to catch a just-finished leader in lib/concurrency/__tests__/leader-lock.test.ts
• 14/14 concurrency tests passing
• Lint clean

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		May 22, 2026 6:02am

[cursor]

PR Summary

Low Risk
Test-only change that adjusts timing/expectations around follower polling; low risk aside from potential flakiness if timing assumptions are wrong.

Overview
Updates the withLeaderLock timeout unit test to more precisely model the poll-loop deadline behavior by shortening maxWaitMs and asserting an explicit third onFollower call for the post-deadline last-chance read that returns the late leader value.

^{Reviewed by Cursor Bugbot for commit f3120cf. Configure here.}

[greptile-apps]

Greptile Summary

Adds a single last-chance onFollower() call after the follower's poll loop exits on deadline, closing the window where a leader could persist between the final in-loop poll and the timeout. The extra DB read only happens in the rare timeout case.

• leader-lock.ts: Three lines appended after the while loop — reads onFollower() once more and returns the result if non-null, otherwise falls through to the existing timeout warning and null return.
• leader-lock.test.ts: New test uses pollIntervalMs: 5 / maxWaitMs: 9 to guarantee the loop exits after exactly two in-loop polls; the third onFollower call lands in the last-chance block, and toHaveBeenCalledTimes(3) confirms it.

Confidence Score: 5/5

Safe to merge — the change is a minimal, well-tested addition that only runs in the already-failing timeout path.

The logic addition is three lines in a clearly understood function with no branching risk. The new test is correctly structured to isolate the last-chance block (third call is definitively post-deadline), and the existing 13 tests continue to cover all other paths. No data is mutated; the worst outcome on any failure is returning null — the same value as before this change.

No files require special attention.

Important Files Changed

Filename	Overview
apps/sim/lib/concurrency/leader-lock.ts	Adds a single last-chance onFollower() call after the poll loop exits, catching results that arrived between the final poll and the deadline. Logic is correct and consistent with existing error-handling patterns.
apps/sim/lib/concurrency/tests/leader-lock.test.ts	New test correctly exercises the last-chance code path using pollIntervalMs: 5 / maxWaitMs: 9 so the loop exits after 2 in-loop polls and the third call hits the post-deadline block; toHaveBeenCalledTimes(3) makes the intent explicit.

Sequence Diagram

sequenceDiagram
    participant F as Follower
    participant DB as onFollower (DB read)

    F->>F: acquireLock → false
    F->>F: "deadline = now + maxWaitMs"

    loop "while Date.now() < deadline"
        F->>F: sleep(pollIntervalMs)
        F->>DB: onFollower()
        DB-->>F: null (leader not done yet)
    end

    Note over F: Loop exits (deadline passed)
    F->>DB: onFollower() [last-chance]
    DB-->>F: value (leader just finished)
    F-->>F: return value

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[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[cursor]

✅ Bugbot reviewed your changes and found no new issues!

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^{Reviewed by Cursor Bugbot for commit f3120cf. Configure here.}