Round 3 review fixes:
- Cost tracking passes None for cost_per_token when model override is
active, letting CostGuard look up pricing by model name instead of
using the default provider's rates (serrrfirat).
- fire_manual() now uses per-user workspace, matching spawn_fire()
pattern (serrrfirat).
- Removed MULTI_TENANT env var — multi-tenant mode is auto-detected
solely from GATEWAY_USER_TOKENS presence (serrrfirat + Copilot).
- Multi-user heartbeat capped at 8 concurrent tasks to avoid flooding
the LLM provider (serrrfirat + Copilot).
- Fixed inject_model_override doc comment accuracy (Copilot).
- Added comment explaining multi-tenant notification routing priority
(Copilot).
Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>