Migration v15 adds a composite index covering the dominant transcripts
query path:
SELECT ... FROM transcripts
WHERE profile_id = ? ORDER BY created_at DESC LIMIT ?
Previously SQLite had to choose between idx_transcripts_profile_id
(filter by profile, then in-memory sort by date) and idx_transcripts_created
(scan dates and filter on profile). Both work fine at hundreds of rows
and degrade past a few thousand.
`migration_v15_creates_profile_created_index` asserts (a) the index exists
and (b) `EXPLAIN QUERY PLAN` shows the planner picks it for the canonical
profile-scoped, date-ordered list query.
Test count assertions in `test_migrations_run_on_empty_db` and
`test_migrations_idempotent` bumped 14 → 15.
https://claude.ai/code/session_0189xUb6ie6t9qHkzatGZ9Rb
f3fd86185e