[M6] Recovery evaluation harness (success, cost, safety)

[askmy-stack]

Why

Compare policies on shared cases with common metrics.

Scope

• Metrics: recovery success, extra steps/cost, irreversible side effects, escalations
• Table output beside detector compare

Acceptance criteria

• Harness CLI
• Results for semantic-drift + at least one other case

References

• Roadmap: docs/roadmap.md
• Related vertical slice: experiments/results/tool-semantic-drift-001.md