Debugging scenarios

Status: Outline. Add short evidence packets—logs, queries, metrics, or code—and ask for a diagnosis sequence.

Scenarios to add

• Stable p50 but rising p99 latency
• Exhausted PHP-FPM worker pool
• N+1 hidden during resource serialization
• Deadlock and duplicate job redelivery
• Growing queue-worker memory
• Cache stampede at expiry
• Tenant data leaked through a cache key
• Deployment where old workers execute new-schema assumptions

For each scenario, ask what to measure first, likely hypotheses, safe mitigation, root fix, and verification.