Deep post-fix bug analysis across five dimensions: root cause categorization, fix failure analysis, prevention mechanisms, systematic expansion, and knowledge capture. Updates .trellis/spec/ guides with lessons learned to prevent recurring bugs. Use when a debugging session completes, after fixing a tricky bug, when the same class of bug keeps recurring, or when you want to capture debugging insights into project documentation.
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tessl review fix ./.agents/skills/break-loop/SKILL.mdWhen debug is complete, use this skill for deep analysis to break the "fix bug -> forget -> repeat" cycle.
Analyze the bug you just fixed from these 5 dimensions:
Which category does this bug belong to?
| Category | Characteristics | Example |
|---|---|---|
| A. Missing Spec | No documentation on how to do it | New feature without checklist |
| B. Cross-Layer Contract | Interface between layers unclear | API returns different format than expected |
| C. Change Propagation Failure | Changed one place, missed others | Changed function signature, missed call sites |
| D. Test Coverage Gap | Unit test passes, integration fails | Works alone, breaks when combined |
| E. Implicit Assumption | Code relies on undocumented assumption | Timestamp seconds vs milliseconds |
If you tried multiple fixes before succeeding, analyze each failure:
What mechanisms would prevent this from happening again?
| Type | Description | Example |
|---|---|---|
| Documentation | Write it down so people know | Update thinking guide |
| Architecture | Make the error impossible structurally | Type-safe wrappers |
| Compile-time | TypeScript strict, no any | Signature change causes compile error |
| Runtime | Monitoring, alerts, scans | Detect orphan entities |
| Test Coverage | E2E tests, integration tests | Verify full flow |
| Code Review | Checklist, PR template | "Did you check X?" |
What broader problems does this bug reveal?
Solidify insights into the system:
.trellis/spec/guides/ thinking guides.trellis/spec/backend/ or frontend/ docsPlease output analysis in this format:
## Bug Analysis: [Short Description]
### 1. Root Cause Category
- **Category**: [A/B/C/D/E] - [Category Name]
- **Specific Cause**: [Detailed description]
### 2. Why Fixes Failed (if applicable)
1. [First attempt]: [Why it failed]
2. [Second attempt]: [Why it failed]
...
### 3. Prevention Mechanisms
| Priority | Mechanism | Specific Action | Status |
|----------|-----------|-----------------|--------|
| P0 | ... | ... | TODO/DONE |
### 4. Systematic Expansion
- **Similar Issues**: [List places with similar problems]
- **Design Improvement**: [Architecture-level suggestions]
- **Process Improvement**: [Development process suggestions]
### 5. Knowledge Capture
- [ ] [Documents to update / tickets to create]The value of debugging is not in fixing the bug, but in making this class of bugs never happen again.
Three levels of insight:
30 minutes of analysis saves 30 hours of future debugging.
IMPORTANT: After completing the analysis above, you MUST immediately:
Update spec/guides - Don't just list TODOs, actually update the relevant files:
cross-platform-thinking-guide.mdcross-layer-thinking-guide.mdcode-reuse-thinking-guide.mdbackend/*.md or frontend/*.mdSync templates - After updating .trellis/spec/, sync to src/templates/markdown/spec/
Commit the spec updates - This is the primary output, not just the analysis text
The analysis is worthless if it stays in chat. The value is in the updated specs.
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