- In `start_session`: increment `flow.usage_count` and set `flow.last_matched_at`
when a flow is matched to a new session; errors are caught without blocking
- In `resolve_session`: recalculate `flow.success_rate` as (resolved / total)
across all sessions ever matched to the flow after each resolution; errors
are caught without blocking the session close
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>