Add structured tracing for Guardian reviews and background scoring

[copyberry]

Add structured tracing for Guardian reviews and background scoring

What changed

• Add debug spans with review, thread, turn, and tool-call identifiers to correlate approval reviews and background scoring.
• Log review retry scheduling with failure details, attempt limits, backoff, and remaining deadline budget.
• Emit warnings for Guardian V2 background scoring failures with the failure reason, context mode, and duration, even when metrics are unavailable.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	🔄 Running since 2026-10-08T21:02:21.475756Z	56d6f02	PR opened

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