Todo 50.1 Metric Key Migration Dedup Plan

Status: in_progress

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