Snapshots containing dates or times are only valid from the timezone they were recorded in. The agent regenerated them on a CI machine with a different timezone, so every stored value is now wrong. Revert the snapshots, pin the timezone explicitly in the test setup, and regenerate once on the pinned value.

```text
my agent bulk-updated snapshots in CI where the timezone differed, baking the wrong timezone into every snapshot
```

## Steps

1. Confirm the damage: search the updated snapshots for date and time strings and compare a few against the committed versions. The diff should show timezone offsets shifting, not real content changes.

   Expected: You can point at snapshot lines where only the timezone offset moved.

2. Revert every snapshot the bulk update touched, using version control. Do not try to hand-fix them; the committed versions are the source of truth.

   Expected: The snapshot files match the last known-good commit again.

3. Pin the timezone explicitly in the test setup: set the TZ environment variable (usually TZ=UTC) in the CI job, in the local test script, and in any test setup file that runs before the suite.

   Expected: Running the suite twice on different machines produces identical date output.

4. Regenerate the snapshots once, on a machine with the pinned timezone, and verify the diff against the reverted files contains only the changes you intended.

   Expected: The regeneration diff is clean: no timezone-only changes anywhere.

5. Make the timezone part of the checked-in config, not tribal knowledge: put TZ in the CI workflow file, the package test script, and a comment in the test setup file.

   Expected: A new contributor running the suite gets the same snapshots on the first run.

## Use this when

- snapshot diffs show timezone offsets shifting after a CI bulk update
- an agent regenerated snapshots on a machine with a different timezone
- date strings in snapshots are wrong in a way that smells like TZ, not data

## Not for this skill when

- the code under test has a real timezone bug (fix the code, not the snapshots)
- snapshots contain no dates or times at all
- only one snapshot changed and it is a genuine content change

## Variant phrasings

- snapshots baked with wrong timezone after bulk update
- agent updated snapshots in CI with different timezone
- timezone offset in snapshots after regenerating in CI

## Why it happens

Most test setups inherit the timezone from the machine they run on. A developer in one timezone records snapshots with local times baked in; CI in another timezone renders the same components with different offsets. When the agent bulk-updates snapshots on the CI machine, it overwrites the good values with wrong-timezone values, and now the snapshots are green in CI but wrong everywhere else. The timezone was never part of the test contract, so nothing flagged the switch.

## Edge cases

- Daylight saving transitions can make the same pinned timezone produce different offsets across the year; UTC sidesteps this entirely.
- If the product genuinely shows local times, test that with explicit timezone fixtures per test rather than relying on the machine default.
- Docker-based CI often defaults to UTC while developer laptops do not; check both before blaming the agent.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_LZOL_AazWks-9CGJ4MBJTg