Scenario: Deadlock-Like Trace in Arbitration Fabric - Interview Scenario

Scenario

Formal reports a long liveness counterexample in a multi-master arbitration path. It is unclear whether this is a genuine deadlock, unfair environment starvation, or a weak progress property.

OBSERVED METRIC
Progress KPI regresses: request age grows unbounded in proof traces while safety checks stay green.

45-MINUTE INTERVIEW FLOW
0-5: define requirement and KPI
5-15: classify first divergence boundary
15-25: identify proving artifact packet
25-35: propose bounded fix with owner
35-45: define validation matrix and rollback

Common traps to avoid

• Masking starvation traces with overly strong fairness assumptions.

• Using only bounded liveness checks without architecture latency rationale.

• Debugging from final symptom cycle instead of first divergence in grant policy.

Scenario debrief

Score scenario responses on assumption discipline, first-divergence analysis, proof-quality evidence, and release-safe mitigation.

requirements -> model -> proof status -> closure decision

closure confidence trend by risk tier

Debrief prompts

1. Which requirement failed first, and is that path legally reachable?

2. Which modeling assumption most influences this result?

3. What smallest reversible action improves confidence without hiding legal behavior?

Key takeaways

• Tie each proof claim to assumption boundaries and reachability evidence.

• Prefer minimal reversible fixes and preserve legal behavior visibility.

Common pitfalls

• Treating runtime reduction as proof-quality improvement without audits.

• Declaring closure while critical covers remain unreachable.

• Using broad waivers instead of first-divergence root-cause ownership.