## TL;DR

Overlapping scans write the baseline concurrently and corrupt it. Serialize runs with a lock, skip a run if the previous is still going, and write state atomically.

## Error

```text
agent's scan scheduler broke: overlapping runs corrupted the baseline
```

## Steps

1. Confirm overlap: check scheduler logs for runs starting before the previous finished. Expected: the overlap proven.
2. Add a lock around the scan so only one runs at a time. Expected: serialization.
3. Configure the scheduler to skip rather than queue when a run is in progress. Expected: no pileup.
4. Write the baseline atomically (temp file plus rename). Expected: readers never see a half-written file.
5. Validate the baseline after each run. Expected: corruption detected immediately if it recurs.

## When to use

- Corrupted baselines with overlapping schedules.
- Designing scan schedulers.

## When not to use

- Single runs corrupting the baseline (different bug).
- The scheduler never overlaps (look elsewhere).

## Tool compatibility

- Cron and job schedulers; file locks; atomic writes.

## Variant phrasings

### baseline corrupted by concurrent scans

Lock them.

### overlapping scan runs

Skip-or-lock.

## Why it happens

Schedulers fire on time, not on completion; slow scans overlap the next trigger and both write the same file.

## Edge cases

- Locks must have timeouts; a dead holder must not block forever.
- Distributed schedulers need distributed locks, not file locks.
- Skipped runs should alert if skips become chronic.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_JnBQlvX7oc-N5o1n1XqPcQ