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A synth that already produced and saved its audio could still return a 500: 'no such table: generation_history' — a DB that somehow missed schema init (init_db's executescript never took) made the history INSERT raise after the clip was done, losing the user's generation to a logging side-effect. - Add db.ensure_schema(): idempotent CREATE ... IF NOT EXISTS + additive column reconcile (no _migrate/alembic), safe to call from a write path. - Generation history write now self-heals: on a sqlite OperationalError it runs ensure_schema() and retries once; if it still fails it logs and returns the audio anyway. A history-logging failure can never fail the generation. Regression test: the write raises 'no such table: generation_history' before the heal and succeeds after (fail-before/pass-after), plus ensure_schema idempotency. Co-authored-by: mergetest <test@local> Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>