#366 HIGH: TenantCache TTL creates stale tenant resolution

## Issue TenantCache in engine/orchestrator.py:55-110 has 5-minute TTL. If a workflow run is deleted from database but still in cache, subsequent operations use stale tenant_id. The cache only evicts entries on access (lazy eviction). Orphaned cache entries for deleted runs remain until accessed. ## Impact - Operations on deleted runs may succeed with wrong tenant context - Potential cross-tenant data access - Audit trail may record wrong tenant ## Location engine/orchestrator.py:55-110 ## Fix - Invalidate cache entries when runs complete/fail/delete - OR reduce TTL significantly - OR query authoritative source for sensitive operations