Safe Refactor

Safe Refactor

Prerequisites

This elixir works best with these skills installed:

When To Activate

Instructions

Phase 1: Assess Risk

If not installed, evaluate:

## Refactor Risk Assessment

**What's changing:**
- [ ] Files affected: [list them]
- [ ] Functions/classes modified: [list them]
- [ ] Estimated lines changed: [number]

**Risk factors:**
- [ ] Touches shared/core code (used by multiple features)
- [ ] Affects data persistence (database, files, cache)
- [ ] Changes public API/interfaces
- [ ] Lacks test coverage
- [ ] Written by someone else / unfamiliar code
- [ ] Production-critical path

**Risk level:** [Low / Medium / High / Abort]

GATE: Do not proceed if:

• Risk is "Abort"
• More than 3 risk factors checked AND no tests exist
• You can't list all affected files

If high risk: Consider breaking into smaller refactors.

Phase 2: Prepare

1. Ensure tests exist (or write them first)

   - [ ] Existing tests cover the behavior being preserved
   - [ ] If no tests: write characterization tests NOW
   

2. Create escape hatch

   git stash  # or commit current state
   git checkout -b refactor/[description]
   

3. Document current behavior

   Before: [How it works now]
   After: [How it should work - must be identical externally]
   

GATE: Do not proceed without:

• Tests that verify current behavior
• Clean git state (can revert easily)
• Clear before/after behavior description

Phase 3: Implement

1. One thing at a time

   • Don't mix refactoring with feature changes
   • Don't fix bugs you discover (note them, fix separately)
   • Don't "while I'm here" other improvements

2. Small commits

   # Good: multiple small commits
   git commit -m "Extract helper function"
   git commit -m "Rename variables for clarity"
   git commit -m "Move file to new location"
   
   # Bad: one giant commit
   git commit -m "Refactor everything"
   

3. Run tests frequently

   • After each logical change
   • Before each commit
   • If tests fail: revert and try smaller steps

4. Preserve behavior exactly

   • No "improvements" to logic
   • No fixing edge cases (that's a separate change)
   • External behavior must be identical

Phase 4: Verify

If not installed:

## Refactor Verification

**Automated checks:**
- [ ] All existing tests pass
- [ ] No new linter errors
- [ ] Type checking passes (if applicable)

**Manual verification:**
- [ ] Tested the primary use case manually
- [ ] Checked one edge case
- [ ] Compared behavior before/after for critical paths

**Regression check:**
- [ ] git diff shows only intended changes
- [ ] No accidental behavior changes
- [ ] No debug code left in

GATE: Do not merge until all checks pass.

If verification fails:

git revert HEAD  # or reset to before refactor
# Start over with smaller scope

Phase 5: Document (Optional)

For large refactors, capture:

• What was refactored and why
• Any tricky parts or gotchas discovered
• Patterns that emerged (potential future skills)

Output Format

## Safe Refactor: [Description]

### Risk Assessment
- Risk level: [Low/Medium/High]
- Files affected: [count]
- Risk factors: [list]

### Preparation
- [x] Tests verified/written
- [x] Branch created: refactor/[name]
- [x] Current behavior documented

### Implementation
- Commits: [count]
- Approach: [brief description]

### Verification
- [x] Tests pass
- [x] Manual verification complete
- [x] No regressions detected

### Learnings (if significant)
[What you'd do differently]

NEVER

• Refactor and add features in the same change
• Skip the risk assessment ("it's just a small cleanup")
• Make large changes without test coverage
• Commit all changes in one giant commit
• "Fix" bugs discovered during refactoring (note them separately)
• Proceed when tests are failing

ALWAYS

• Assess risk before starting
• Ensure tests exist (write them if needed)
• Work on a branch with escape hatch ready
• Make small, incremental commits
• Run tests after each logical change
• Verify behavior is preserved exactly

Example

User: "Refactor the authentication module to use the new token format"

Phase 1 - Risk Assessment:

Refactor Risk Assessment:

• Files affected: auth.ts, token.ts, middleware.ts, 12 test files
• Risk factors: ✓ Core code, ✓ Production-critical, ✓ Written by someone else
• Risk level: High

Recommendation: Break into smaller refactors:

1. First: Add new token format support alongside old
2. Second: Migrate consumers one by one
3. Third: Remove old format

Phase 2 - Prepare:

• Existing tests cover token generation and validation
• Created branch: refactor/token-format-v2
• Documented: Old format is JWT with RS256, new format adds typ header

Phase 3 - Implement:

Making changes incrementally...

• Commit 1: "Add TokenV2 class with new format"
• Commit 2: "Add feature flag for token format"
• Commit 3: "Update token generation to use flag"
• Tests passing after each commit ✓

Phase 4 - Verify:

• All 47 auth tests pass
• Manual test: login flow works with both formats
• Manual test: token refresh works
• git diff shows only intended changes

Ready to merge.