## TL;DR
A backfill that never converges has partitions that fail and retry forever: poisoned data, a broken task for certain keys, or a range that grows as fast as it fills. Measure per-partition progress, quarantine the failing partitions, and complete the rest. An 80 percent backfill with a known bad-partition list beats a 0 percent backfill still looping.

```text
agent loop detected: partition backfill never converges, backfill failed
```

## Use this when
- A partition backfill runs without converging.
- The same partitions fail and retry repeatedly.
- Completed partition count stalls while attempts climb.

## Not for this skill when
- The backfill is slow but the completed count grows. That is patience, not a loop.
- The backfill failed fast entirely. That is a different failure.

## Steps
1. Measure per-partition state: completed, failed, and attempt counts. Note the distribution. Verify: the stall is localized
2. Identify the partitions that fail repeatedly and read one failure in full. Note the cause. Verify: the poison is named
3. Quarantine the bad partitions: exclude them and let the rest complete. Note the quarantine list. Verify: the good work finishes
4. Fix the quarantined partitions deliberately: data repair, code fix, or manual load. Note the fix. Verify: the bad partitions get real attention
5. Record the convergence: what completed, what was quarantined, what remains. Note the record. Verify: the outcome is explicit, not infinite

## Variant phrasings
### backfill stuck retrying partitions
The symptom phrasing.
### partition backfill poison partitions
The cause-shaped search.

Compatibility: Partitioned backfills on any orchestrator. The pattern is orchestrator-independent.

## Why it happens
Backfills are loops over partitions, and a poisoned partition turns the loop into an infinite one: fail, retry, fail, retry, while the completed count never moves. The aggregate view (backfill running) hides the per-partition truth (seven partitions failing forever). Quarantine is the circuit breaker: it lets the healthy majority finish and converts the poisoned minority from an infinite loop into a finite, named work list. Convergence is a decision, not just a property.

## Edge cases / pitfalls
- Quarantined partitions are debt. Track them or they become permanent gaps.
- A backfill range defined as up-to-now grows while it runs and never converges by construction. Freeze the end date.
- Retrying the whole backfill after quarantine re-runs completed partitions wastefully. Resume from the quarantine list.
- Some partitions fail from transient downstream issues and succeed later. Distinguish poisoned from unlucky before quarantining.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst__v5HOXU8T60uz70Dhwz6uQ