backprop

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellNone observedNo commands run in the source
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass.

Audit 0.4.1 · source sha 4ddfda34b42a · 20 Oct 2026Report an issue or request a re-scan

• Publisherjuliusbrussee GitHub userOwner of the repository this skill is read from
• Source folderjuliusbrussee/cavekit/skills/backpropThe exact folder we audited
• LicenceMITAs the repository states it
• Commit pinned for this verdict4ddfda34b42aA new audit runs when the source changes
• Repository statusNot archivedLast push 66 days ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its description: Bug → spec protocol. When a bug is found or a test fails, trace the cause, decide whether a new §V invariant would catch recurrence, append to §B. This is the one non-obvious thing SDD does that plan-then-execute…

---
name: backprop
description: |
  Bug → spec protocol. When a bug is found or a test fails, trace the cause,
  decide whether a new §V invariant would catch recurrence, append to §B.
  This is the one non-obvious thing SDD does that plan-then-execute doesn't.
  Triggers on test failure, bug report, post-mortem, or explicit user ask.
---

# 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.

Excerpt, first 2,610 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

git clone https://github.com/juliusbrussee/cavekit
git -C cavekit checkout 4ddfda34b42a

Works in

1. 2026-10-20
   ✓SAFE B 89 / 100

   first audit · source 4ddfda34b42a

Questions about backprop

• github.com/juliusbrussee/cavekit/tree/main/skills/backprop — the audited source at commit 4ddfda34b42a and every finding aboveObserved · 20 Oct 2026

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