# Todo 50.1 Metric Key Migration Dedup Plan

**Status:** done

## Goal

Allow additive metrics migration to open an experimental database that already contains duplicate non-null metric keys.

## Scope

- Before creating `usage_stats_metric_key_uq`, delete duplicate rows for the same `(session_id, metric_key)` while retaining the earliest row by `id`.
- Never deduplicate `NULL` metric keys used by legacy usage rows.
- Keep cleanup and unique-index creation inside the serialized migration transaction.
- Cover concurrent store initialization after duplicate cleanup.

## Files

- Modify: `src/agent_lab/infrastructure/sqlite_store.py`
- Modify: `tests/test_sqlite_store.py`

## Verification

- `uv run pytest tests/test_sqlite_store.py -q`
- repeat concurrent migration test
- `uv run pytest`
- `git diff --check`

## Observe / Update

- Migration retains `MIN(id)` for each duplicate non-null `(session_id, metric_key)` and preserves all legacy `NULL` keys.
- Cleanup and unique-index creation run inside the serialized `BEGIN IMMEDIATE` migration.
- SQLite focused tests passed (`12 passed`), concurrent initialization passed 20 repeated runs, and the full suite passed (`405 passed`).