## TL;DR
The agent's own earlier run left the database dirty, so the tests failed and got quarantined for a mess the agent made. Reset the database between healing runs, make test setup hermetic (migrate and seed from scratch per run), and re-verify every quarantine decision against a clean database before accepting it.

## The symptom
```text
agent quarantined tests that failed only because its own prior run left the database dirty
```

## Steps
### 1. Prove the database was dirty
Inspect the test database after the agent's run: leftover rows, half-applied migrations, or sequences advanced past the seed state. Compare against a freshly seeded database.
Expected: Leftover state from the agent's prior run, absent in a clean seed.

### 2. Reset and rerun cleanly
Drop, migrate, and reseed the test database from scratch, then rerun the quarantined tests with no agent intervention in between.
Expected: The quarantined tests pass on the clean database.

### 3. Unquarantine and make setup hermetic
Remove the quarantine flags. Fix the test setup so each run starts from a known state: transactional rollbacks, or full reset in setup.
Expected: Tests pass consistently regardless of what ran before them.

### 4. Isolate the healer's side effects
Run healing attempts against a throwaway database (a cloned schema or a per-run database name) so the agent's experiments can never pollute the suite's database.
Expected: Agent runs leave the shared test database untouched.

## When to use
- Quarantined tests pass on a freshly seeded database
- The agent ran experiments against the suite's test database
- Failures mention duplicate keys, stale rows, or unexpected existing data

## When not to use
- Tests fail on a clean database too (the quarantine may be legitimate)
- The pollution comes from other tests, not the agent (fix test isolation)
- The database is intentionally shared across tests (then the design needs review)

## Why it happens
Healing agents iterate: they run the test, tweak, rerun. Each attempt writes to the database, and without a reset between attempts the state accumulates. Eventually the test fails because of the accumulated mess, and the agent quarantines the victim instead of cleaning up its own side effects.

## Edge cases
- Parallel test runs sharing one database: give each worker its own database.
- Migrations that are not reversible: snapshot and restore instead of migrate-down.
- External services with state (queues, buckets): reset those too, not just the DB.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_ujNO46i__XP-8Bt6bFra-A