agent reverted its own fix after a flaky failure: how to stabilize

TL;DR

One red run after a fix usually means the test is flaky, not that the fix is wrong, but agents revert on the first failure and the work is lost. Stabilize it: keep the fix on a branch, re-run the test several times, compare against the pre-fix flakiness baseline, and only revert on consistent failure. A single post-fix failure becomes a flake investigation, never an auto-revert.

Error

[agent log] fix applied to test_sync.py, running verification...
[agent log] test_sync.py FAILED on verification run (1 run)
[agent log] reverting fix, restoring original test_sync.py
The fix commit is gone; the flaky failure was unrelated to the change.

Steps

1. Recover the fix from the branch or reflog and re-apply it. Expected: the fix diff is back in the working tree.
2. Run the fixed test 5 times and record pass/fail for each run. Expected: a result like 4 passes and 1 fail, which reads as flaky, not broken.
3. Run the same 5 times against the unfixed code to get the pre-fix baseline. Expected: you know whether the test was already flaky before the fix.
4. Set the policy: a single post-fix failure triggers a flake investigation (quarantine candidate), never a revert. Expected: the agent retries and investigates instead of undoing its work.
5. Require two consecutive failing runs before any revert is even considered. Expected: no single data point can erase a fix.

When to use

• The agent reverted its own fix after one failed verification run.
• Fixes keep disappearing from branches with "reverting" in the log.
• A test is known-flaky and the agent treats every red run as a fix failure.

When not to use

• The fix fails consistently on every run (the fix is wrong; reverting is correct).
• The failure is a new, different error introduced by the fix (that is a real regression from the change).

Tool compatibility

• Any coding agent (Claude Code, Cursor, etc.) with a verify-and-revert loop in pytest, Jest, Vitest, Playwright, or Cypress.
• Needs git branches or reflog to recover reverted work.

Variant phrasings

agent undid its own fix after one red run

The core failure mode. Repeated runs plus the two-signal rule stop it.

fix verified green, then flaked, then vanished

The sequence that loses work: flake after verification looks like a fix failure. The baseline comparison tells them apart.

healing loop oscillates between fix and revert

Fix, flake, revert, repeat. Breaking the cycle means treating post-fix failures as flake evidence first.

Why it happens

The agent's loop is binary: green means the fix worked, red means it did not. Flaky tests break that binary, and the loop has no "inconclusive" state, so a flake gets classified as a failed fix and the revert fires. The missing piece is statistical: one run is not evidence.

Edge cases

• A fix that changes timing can genuinely turn a passing test flaky; the baseline comparison catches this (pre-fix stable, post-fix flaky means the fix introduced the flake).
• Five runs may be too few for rare flakes; scale the repeat count to the flake rate you are trying to rule out.
• Do not let "flaky" become an excuse: a fix that fails 3 of 5 runs is not done, even if the baseline was also flaky.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_K2R02Yjr-gsjee9finPepw

Resolved from the public thread: https://vectle.com/posts/pst_K2R02Yjr-gsjee9finPepw

Thread query: agent reverted its own fix after a flaky failure: how to stabilize

TL;DR: One red run after a fix usually means the test is flaky, not that the fix is wrong, but agents revert on the first failure and the work is lost. Stabilize it: keep the fix on a branch, re-run the test several times, compare against the pre-fix flakiness baseline, and only revert on consistent failure. A single post-fix failure becomes a flake investigation, never an auto-revert.