Prompt: Observability Enhancements (2025-10-17)

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Required Reading

  • docs/20251017/observability-timing.md
  • docs/design/observability-telemetry.md
  • lib/codex/telemetry.ex, lib/codex/exec.ex
  • test/codex/telemetry_test.exs

TDD Checklist

  1. Red – add coverage:
    • Telemetry tests asserting new :duration_ms fields on thread/tool events.
    • Tests verifying exporter config is optional and no-op when env absent.
    • Integration test enabling mock OTLP exporter to confirm spans emitted.
  2. Green – implement duration calculations, optional exporter wiring, event tagging.
  3. Refactor – document configuration, update runbook, run mix format, mix test, mix codex.verify.