Skill1k repo starsupdated 26d ago

backprop

Backprop is a structured bug-fixing workflow that treats specification updates as equally important as code fixes. When a test fails, a user reports a bug, or a production incident occurs, backprop traces the root cause, analyzes whether it reveals a missing invariant in the spec, proposes a testable specification change, generates a test for the new rule, verifies the fix across the suite, and commits everything together. This approach prevents bug recurrence by embedding the lesson into the specification itself rather than just patching the code.

View source Repository: cavekit

Install in Claude Code

Copy

git clone --depth 1 https://github.com/JuliusBrussee/cavekit /tmp/backprop && cp -r /tmp/backprop/skills/backprop ~/.claude/skills/backprop

Then start a new Claude Code session; the skill loads automatically.

Definition

SKILL.md

# backprop — bug → spec

Plan-then-execute fixes the code & forgets.
SDD fixes the code AND edits spec so recurrence is impossible.
That edit is backprop.

## WHEN TO BACKPROP

- Test failed at `/build` verification.
- User reports bug.
- Post-mortem after production incident.
- `/check` flags VIOLATE with root cause found.

## SIX STEPS

### 1. TRACE
Read failure output / bug report.
Find exact file:line of wrong behavior.
Name root cause in one caveman sentence.

### 2. ANALYZE
Ask three questions:
- Would a new §V invariant catch this class of bug? (most common: yes)
- Is §I wrong — did spec claim shape the code cannot deliver? (sometimes)
- Is §T wrong — did we build the wrong thing? (rare but real)

### 3. PROPOSE
Draft the spec change. Never skip §B; §V/§I/§T are case-by-case.

Template:
```
§B row: B<next>|<date>|<root cause>|V<N>
§V line: V<next>: <testable rule that would have caught it>
```

Example:
```
§B row: B3|2026-04-20|refund job ran twice on retry|V7
§V line: V7: ∀ refund → idempotency key check before charge reversal
```

### 4. GENERATE TEST
New invariant without test = lie. Add failing test first.
Name test so it cites the invariant: `TestV7_RefundIdempotent`.

### 5. VERIFY
Fix code. Run test. Must pass. Run full suite. Must not regress.

### 6. LOG
Commit spec edit + test + code fix together.
Commit msg: `backprop §B.<n> + §V.<N>: <one-line cause>`.

## WHAT MAKES A GOOD INVARIANT

- Testable in code (grep-able or assert-able).
- Scoped to a behavior, not a file.
- Stated positively when possible (`! hold` over `⊥ forbid`).
- References §I surface where it applies.

**Bad**: V8: code should be correct.
**Good**: V8: ∀ pg_query ! params interpolated via driver, ⊥ string concat.

## WHEN NOT TO ADD §V

- Bug was purely mechanical typo with no class (`i++` vs `i--` in throwaway).
- Fix is a one-time migration.
- Root cause is external dep (upgrade deps instead, note in §C).

Still append §B entry — record that this failure mode was considered. Future bug with same smell → §B search shows precedent.

## OUTPUT SHAPE

Every backprop run produces:
1. §B entry (always).
2. §V entry (usually).
3. Test file (when §V added).
4. Code fix.
5. One commit.

No dashboards. No log files. SPEC.md + git is the full history.