Regression Check

Check for regressions in: $0

Depth: $1 (default: deep)

Steps

1. Map the change surface — Identify what was modified:

   • Which files changed?
   • Which functions/exports were modified?
   • Did any public interfaces change (function signatures, types, API responses)?

2. Trace downstream consumers — For each changed export/interface:

   • Who imports this module? (grep for import statements)
   • Who calls these functions? (find all call sites)
   • Are there any dynamic consumers (string-based imports, reflection)?

3. Classify risk per consumer:

   • Breaking: signature changed, return type changed, thrown error changed
   • Behavioral: same interface but different output for some inputs
   • Safe: internal-only change, consumers unaffected

4. Check test coverage:

   • Are the changed code paths covered by existing tests?
   • Do existing tests assert on the specific behaviors that changed?
   • Are downstream consumers tested with integration tests?
   • Run existing tests — do they still pass?

5. Identify coverage gaps:

   • Consumers with no tests at all
   • Tests that pass but don't assert on the changed behavior
   • Missing edge case tests for new code paths

6. Check non-obvious regressions:

   • Performance: did the change add a loop, remove a cache, increase query count?
   • Security: did the change modify auth, validation, or data access?
   • Ordering: does the change affect sort order, event sequence, or render order?
   • Side effects: does the change add/remove writes, notifications, or logging?

Output Format

## Regression Check: <target>

### Change Summary
- **Files changed**: N
- **Public interfaces modified**: <list>
- **Risk level**: low | medium | high

### Affected Consumers
| Consumer | Risk | Test Coverage | Action Needed |
|----------|------|---------------|---------------|
| <file>   | breaking/behavioral/safe | covered/partial/none | <action> |

### Coverage Gaps
1. **<gap>**: <what's not tested + suggested test>

### Non-obvious Risks
1. **<risk>**: <explanation>

### Recommended Actions
- [ ] <action 1>
- [ ] <action 2>

Constraints

• Trace actual import chains, don't guess at consumers
• Run existing tests if possible — don't just check if they exist
• Distinguish "no test coverage" from "tests exist but don't cover this path"
• For deep mode, follow the chain at least 2 levels (consumer's consumers)