✨ feat(playbook): add syntax book and codex skills tooling

codex/skills/root-cause-tracing/SKILL.md

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+---
+name: root-cause-tracing
+description: Root cause analysis (RCA) and tracing failures back to the original trigger across layers. Triggers: root cause, RCA, tracing, 回溯, 根因, 追溯, 为什么会发生.
+---
+
+# Root Cause Tracing（根因溯源 / RCA）
+
+## When to Use
+- Incidents, regressions, flaky tests, recurring bugs
+- “Fix the symptom” patches where the underlying trigger is unknown
+- Multi-layer failures (client → service → DB → async jobs)
+
+## Inputs（required）
+- Evidence: logs, stack traces, metrics, failing test output
+- Timeline: when it started, what changed, rollout events
+- Scope: affected users/paths, frequency, severity
+- Verification: how to reproduce (or how to detect reliably)
+
+## Procedure（default）
+1. **Frame the Failure**
+   - Define expected vs actual behavior
+   - Identify the earliest known bad signal
+
+2. **Trace Backwards**
+   - Walk back through layers: surface error → caller → upstream trigger
+   - Look for the first point where invariants were violated
+
+3. **Find the Trigger**
+   - What input/state/sequence causes it?
+   - What changed around that area (code/config/deps/data)?
+
+4. **Fix at the Right Layer**
+   - Prefer root-cause fix + defense-in-depth guardrails
+   - Add regression test or a deterministic repro harness
+
+5. **Validate**
+   - Reproduce before fix; verify after fix
+   - Add monitoring/alerts if appropriate
+
+## Output Contract（stable）
+- Summary: what broke and impact
+- Root cause: the earliest causal violation + why it happened
+- Trigger: minimal repro steps / conditions
+- Fix: what changed and why it prevents recurrence
+- Verification: tests/commands + evidence
+- Follow-ups: guardrails/observability/rollout notes
+
+## Guardrails
+- Don’t stop at “where it crashed”; find “why the bad state existed”
+- Separate contributing factors vs root cause
+- Avoid speculative RCA; label assumptions and request missing evidence
+