Fixes from review comments on #1614:
- Cost tracking now uses the override model name (not active_model_name)
when a per-user model override is active, for accurate attribution.
- Multi-user heartbeat runs per-user checks concurrently via JoinSet
instead of sequentially, preventing one slow user from blocking others.
- Per-user failure counts tracked independently; users exceeding
max_failures are skipped (matching single-user semantics).
- per_user_daily_cost HashMap pruned on day rollover to prevent
unbounded growth in long-lived deployments.
- Doc comment fixed: says "routines" not "active routines".
Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
