Prevent Regression

/prevent-regression

Swift 6.3.3 exact-property-type guard

Use scripts/stage_swift_state_guard.py only after a fresh accepted Swift enum proposal and a second content-addressed acceptance of the migrated tree and exact buildable String reversion. Keep sibling _swift-semantic-readonly. The skill stages but never installs one same-module compile-time property-type guard derived from the accepted owner, member, and existing enum identity. It proves the accepted migrated tree passes build/check/smoke and guard typecheck, then proves the accepted reversion still passes native gates without the guard but fails with it. Case/raw mappings remain proposal evidence rather than a guard claim; runtime behavior, Codable/reflection, dynamic/protocol dispatch, frameworks, generated inputs, external variants, and compatibility remain outside the guard.

C# staged exact-property-type guard

Use scripts/stage_csharp_state_guard.py only after a fresh accepted C# enum migration and current sibling _csharp-semantic facts. Read knowledge/csharp-v1.md for the exact command. The skill stages but never installs one exact property-type compile guard and proves a disposable string reversion fails. Wire values, runtime behavior, other properties, generated code, frameworks, external callers, and binary compatibility remain outside the claim.

Kotlin/JVM 2.4.10 exact-type guard

Trigger this branch only from a fresh accepted Kotlin enum proposal and a second content-addressed migration acceptance. Keep sibling _kotlin-semantic, read ../_kotlin-semantic/GUIDE.md, and enter through scripts/stage_kotlin_state_guard.py. It stages but never installs one compile-time exact-property-type assertion and proves an accepted buildable String reversion fails with the guard. It does not protect wire values, reflection, delegation, generated/plugin sources, Gradle variants, Java/framework/external callers, runtime behavior, JVM ABI, or general Kotlin lint coverage.

C++20 branch

Use scripts/stage_cpp_state_guard.py with a fresh accepted migration and all five human approvals; run it with --help for the exact CLI. It stages, but never installs, one std::is_same_v guard for an exact namespace-qualified field and proves one disposable type regression fails. It makes no broader ODR/ABI, specialization, overload/dispatch, external-variant, or runtime claim.

C17 branch

Use scripts/generate_c_state_guard.py on an accepted C enum proposal, then verify the staged bundle with scripts/verify_c_state_guard.py; run each with --help for the exact CLI. This branch stages but never installs one exact- field _Static_assert/_Generic type guard; values, assignments, aliases, runtime behavior, other fields, and general lint coverage remain unresolved.

PHP and Ruby

For an accepted PHP enum proposal, read _php-proposal/GUIDE.md. For an accepted Ruby RBS proposal, read _ruby-semantic/PROPOSAL-GUIDE.md. Both branches stage and verify one exact reviewed field guard; neither installs it.

Dart exact-field guard

After a human accepts the Dart enum proposal, stage—not install—a dependency-free project-owned guard for that exact reviewed public field. The verifier proves a good disposable tree passes and a buildable String reversion fails specifically because of the staged guard.

SKILL_ROOT=".agents/skills/on-demand/prevent-regression"
python3 "${SKILL_ROOT}/scripts/generate_dart_state_guard.py" \
  --project-root "$PWD" --evidence-dir reports/implicit-state/dart \
  --acceptance reports/implicit-state/dart/acceptance.json \
  --targets reports/extract-enum/dart/targets.json \
  --accepted-review reports/extract-enum/dart/accepted-review.json \
  --output-root "$PWD/reports/prevent-regression/dart-state"
python3 "${SKILL_ROOT}/scripts/verify_dart_state_guard.py" \
  --project-root "$PWD" --stage reports/prevent-regression/dart-state

This is one field guard, not a universal lint or a runtime/serialization invariant. Audited host source is never modified.

Rust exact-field guard

After a human accepts an extract-enum proposal, require a SHA-bound rust-enum-review-v1 acceptance artifact. Stage—not install—a project-owned Cargo integration test that asserts one public owner/public field has the reviewed enum type, then verify it with locked/offline metadata, check, test, Clippy, and rustfmt. Private fields abstain; this is not a general Rust lint.

SKILL_ROOT=".agents/skills/on-demand/prevent-regression"
OUT="$PWD/reports/prevent-regression/rust-state"
python3 "${SKILL_ROOT}/scripts/generate_rust_state_guard.py" \
  --targets "$PWD/reports/extract-enum/rust/targets.json" \
  --accepted-review "$PWD/reports/extract-enum/rust/accepted-review.json" \
  --project-root "$PWD" --output-root "$OUT"
python3 "${SKILL_ROOT}/scripts/verify_rust_state_guard.py" \
  --stage "$OUT" --project-root "$PWD" \
  --output "$OUT/verification.json"

You are the orchestrator for turning a closed cleanup into a permanent guardrail. Invocation only stages a proposal below reports/prevent-regression/<id>/; it never authorizes rollout. Stage rule, fixture, and ready-to-apply wiring at their repo-relative destination paths, then let the human install or discard them.

How success is judged

• Emit, never install, the artifact and verification recipe.
• Paste the real verifier result: BAD_RC=1 and GOOD_RC=0 for lint guards, or focused test output for behavioral guards.
• Prove the historical fire and current clean result; fixtures cover every matched anti-pattern plus legitimate forms.
• Use _common/skill-conventions.md, agents/rule-designer.md, and the bundled generation/verifier helpers for the shared report shape.

Closed-state guard

For the reviewed first-party status / phase / state path, use the bundled guard directly after installation:

python3 scripts/stringly_status_guard.py <file-or-directory>

It blocks a bare string Django field, comparison, or assignment and accepts only a reasoned # noqa: stringly-status: <reason> vendor boundary. This is a family-local reference guard; it does not generate or install unrelated general-purpose rules.

TypeScript closed-state guard

Stage—not install—the family-local Compiler API guard for a reviewed closed TypeScript field. It covers direct/reversed comparisons, one-hop const aliases, plain/??=/chained assignments, and transparent parentheses. A pinned host TypeScript package plus tsconfig are required; unsupported general dataflow, ORM behavior, and root lint wiring remain out of scope.

ID="typescript-state"
OUT="reports/prevent-regression/$ID"
node .claude/skills/prevent-regression/scripts/generate_typescript_state_guard.mjs \
  --id "$ID" \
  --project-root "$(pwd)" \
  --tsconfig "$(pwd)/tsconfig.json" \
  --output-root "$OUT"

node .claude/skills/prevent-regression/scripts/verify_typescript_state_guard.mjs \
  --rule "$OUT/scripts/lint/no_stringly_state.mjs" \
  --bad "$OUT/tests/lint/no_stringly_state_bad.ts" \
  --bad-tsx "$OUT/tests/lint/no_stringly_state_bad.tsx" \
  --good "$OUT/tests/lint/no_stringly_state_good.ts" \
  --good-tsx "$OUT/tests/lint/no_stringly_state_good.tsx"

The report stages guard, TS/TSX fixture pairs, and host-wiring.diff; paste BAD_RC=1/GOOD_RC=0. A reasoned noqa only suppresses a Compiler-resolved vendor receiver, never a filename or forged first-party comment. The serial integrator owns staged wiring.

Checked-JavaScript closed-state guard

Retain complete checked-JavaScript detector evidence and manifest first. The generator accepts only at least one proven first-party operation from an allowJs + checkJs host Compiler API run; partial/unsupported evidence exits 2 rather than fabricating findings.

ID="javascript-state"
OUT="reports/prevent-regression/$ID"
node .claude/skills/prevent-regression/scripts/generate_javascript_state_guard.mjs \
  --id "$ID" \
  --project-root "$(pwd)" \
  --config "$(pwd)/jsconfig.json" \
  --findings reports/implicit-state/findings.jsonl \
  --manifest reports/implicit-state/manifest.json \
  --output-root "$OUT"

node .claude/skills/prevent-regression/scripts/verify_javascript_state_guard.mjs \
  --rule "$OUT/scripts/lint/no_stringly_state_javascript.mjs" \
  --bad "$OUT/tests/lint/no_stringly_state_bad.js" \
  --bad "$OUT/tests/lint/no_stringly_state_bad.jsx" \
  --bad "$OUT/tests/lint/no_stringly_state_bad.mjs" \
  --bad "$OUT/tests/lint/no_stringly_state_bad.cjs" \
  --good "$OUT/tests/lint/no_stringly_state_good.js" \
  --good "$OUT/tests/lint/no_stringly_state_good.jsx" \
  --good "$OUT/tests/lint/no_stringly_state_good.mjs" \
  --good "$OUT/tests/lint/no_stringly_state_good.cjs"

The proposal stages four fixture pairs and wiring; paste BAD_RC=1/GOOD_RC=0. Coverage is direct/reversed comparison, assignment, and one-hop const aliases on JSDoc-closed fields; vendor noqa requires Compiler API evidence. The serial integrator owns installation.

Go closed-state guard

After a human accepts a Go proposal, read and follow knowledge/go-state.md. Load that file only for Go work. Never weaken an unavailable semantic closure to a field-name regex.

Java 17 exact-authority guard

After a human accepts a Java enum proposal, stage—not install—a guard from its targets.json. It copies the accepted qualified owner, field, source fingerprint, and family-local JDK compiler helper. The staged rule checks only that compiler-resolved direct String field; it does not broadly match every field named state, status, or phase. It catches bare assignments, String.equals/Objects.equals, and unsafe ==/!= while that exact field is still String.

OUT="${OUT:-reports/prevent-regression/java-job-status}"
TARGETS="${TARGETS:-reports/extract-enum/java-job-status/targets.json}"
SKILL_ROOT=""
for SKILL_CANDIDATE in \
  ".agents/skills/on-demand/prevent-regression" \
  ".agents/skills/prevent-regression" \
  ".claude/skills/prevent-regression"
do
  if [ -f "${SKILL_CANDIDATE}/SKILL.md" ]; then
    SKILL_ROOT="$(cd "${SKILL_CANDIDATE}" && pwd)"
    break
  fi
done
if [ -z "${SKILL_ROOT}" ]; then
  printf '%s\n' "prevent-regression is not installed in .agents/skills/on-demand, .agents/skills, or .claude/skills" >&2
  exit 2
fi
python3 "${SKILL_ROOT}/scripts/generate_java_state_guard.py" \
  --targets "$TARGETS" \
  --project-root "$(pwd)" --output-root "$OUT"
RULE="$(find "$OUT/scripts/lint" -maxdepth 1 -name 'no_stringly_state.py' -print -quit)"
python3 "${SKILL_ROOT}/scripts/verify_java_state_guard.py" \
  --rule "$RULE" --authority "$OUT/authority.json" \
  --bad "$OUT/tests/lint/bad/Job.java" --good "$OUT/tests/lint/good/Job.java" \
  --project-root "$(pwd)"

Install find-implicit-state alongside this skill so the generator can copy its helper; a missing helper or JDK 17 exits 2 rather than falling back to a name regex. The verifier pastes BAD_RC=1, GOOD_RC=0 and compiles both fixtures with javac --release 17 -proc:none. This branch modifies only the staged proposal directory, never host guard files; a human integrator owns any later installation, native check, and rollback.

Argument parsing

Four forms. Detect and route:

Form A — Cluster ID from a recent scan

Pattern: cluster:<id>, delete:<id>, fix:<id>, semantic:<id>, dormant:<id> — anything /fix-workflow accepts.

Load the corresponding triage entry from reports/<scan>/latest/report.md or triage.md and extract:

• files touched
• fix shape (e.g. quasi_dead_broken, extract_helper)
• the git commit(s) that landed the fix (from the learnings log or git log --grep=<id>)

Form B — Explicit pattern description

A sentence plus an optional path:<regex> qualifier. Example:

"bare int(request.POST.get(...)) without safe_int in views" path:core/views/**/*.py

Treat the sentence as the rule intent. Before producing a proposal, ask for one clarification round if the path scope or anti-pattern AST shape is ambiguous.

Form C — --dogfood <rule-name>

Used when the rule script already exists under scripts/lint/ and you only need to (re)wire it, regenerate fixtures, or refresh the CLAUDE.md entry. Skip Phase 1 and start at Phase 2.

Form D — Product-topology guard template

Pattern: topology:<route-ownership|workflow-registry|frontend-boot|site-endpoints|doc-route-drift>.

Use this when a workflow cleanup has already landed and the user wants to prevent drift from returning. The skill should start from the corresponding product-topology report, not from a raw grep:

• route-ownership: block new workflow routes from being added to the global root URL file once an include boundary exists.
• workflow-registry: block new sidebar/dashboard step definitions outside the canonical registry.
• frontend-boot: block new template-level window.* globals outside the canonical boot payload.
• site-endpoints: block hardcoded registry-owned /api/sites/<site_id>/... consumer strings once the workflow boot payload exposes endpoint keys.
• doc-route-drift: add a scheduled or diff-scoped docs-vs-routes check when route docs repeatedly drift.

Core beliefs

1. Ruff first. Use a custom rule only where Ruff is silent or too broad.
2. Diff-scope and reasoned escapes. Hooks inspect changed files; custom noqa markers require a non-empty reason.
3. Fixture truth. Every matcher branch fires in bad fixtures and stays quiet in good fixtures; the verifier is the proof.
4. One invariant, one commit. Bundle rule/test, fixtures, verifier, and staged wiring so a revert and bisect remain meaningful.
5. Choose the right peer. Use lint for local shape, tests for behavioral contracts, and audit bands only when neighbor/path context is essential.
6. Protect an accepted convention. Derive registry facts where possible; do not guard topology before its canonical shape exists.

New-Feature Guardrail Prompts

When a feature establishes a reusable convention, ask whether a lightweight guard belongs with it: reverse-backed route tests before endpoint lints; one boot payload plus a retired-global check; typed state authority from creation; a dormant sweep or quarantine for prototype remnants; endpoint/credential tests before bespoke lints; and broker-failure cleanup tests for safe dispatch.

Phase 1 — Pattern discovery

Pre: argument resolved. Post: reports/prevent-regression/<id>/pattern.md exists with the rule intent, path scope, file suffixes, and match shape.

Run git show <commit> for the fix commit(s). Read the diff. Classify:

• Ruff-coverable: the pattern corresponds to an existing ruff rule (consult https://docs.astral.sh/ruff/rules/). Emit a pyproject.toml diff that enables the rule and optionally narrows per-file-ignores. Skip to Phase 4.
• Custom rule: the pattern is narrower, domain-specific, spans a non-Python language, or requires looking at source comments (e.g. the allow-list shape). Proceed to Phase 2.

Record the classification, rule name, path scope, file suffixes, and anti-pattern shape. For Python, describe the AST shape (what ast.walk looks for). For JS/templates/docs, describe the lexical or parser shape and the false-positive boundaries. Use symbolic names in prose — see _common/skill-conventions.md "No raw line numbers".

Phase 2 — Rule script

Pre: classified as custom rule. Post: scripts/lint/<rule>.py exists and is smoke-tested.

Contract for every custom rule:

• Stdlib-only. Runs under bare python3 (no .venv required).
• CLI: accepts <file> / <directory> positionals OR --stdin --filename=<name>; exit 0 on clean, 1 on violations, 2 on invocation error. Directory scans use scripts/lint/path_utils.py for skip directories and expand only the rule's suffixes.
• Output: one line per violation, format <path>:<line>:<col>: <rule>: <message>.
• Allow-list: <comment> noqa: <rule>: <reason> on any line of the matched span, reason regex \S (non-empty). Use # for Python and // for JS.

silent_catch.py is the Python reference implementation. For JS lexical guards (no_site_endpoint_sprawl.py was the source host's exemplar — not shipped in this ecosystem;

keep this shape: suffix expansion, template-literal/string-concat matching, blockable comments, and a reason-required // noqa.

Phase 3 — Fixtures

Pre: rule script works on synthetic input. Post: tests/lint/<rule>_bad.<ext> + tests/lint/<rule>_good.<ext> exist and verify_rule.py passes.

<rule>_bad.<ext> must contain every variant of the anti-pattern the rule is supposed to catch — at minimum one example per branch of the rule's matcher. <rule>_good.<ext> must contain the legitimate patterns the rule must NOT flag: narrow exceptions, logged paths, re-raises, allow-listed cases.

Python fixtures carry # ruff: noqa at the top so they don't double-fail the standard ruff pass. Non-Python fixtures use the normal comment style for explanatory fixture comments.

Run:

python3 .claude/skills/prevent-regression/scripts/verify_rule.py \
  --rule scripts/lint/<rule>.py \
  --bad tests/lint/<rule>_bad.<ext> \
  --good tests/lint/<rule>_good.<ext>

It must report BAD_RC=1 (violations fired) and GOOD_RC=0 (no false positives). If either is wrong, iterate on the rule or fixtures.

Phase 3b — Test-only guard

Use this when a focused test expresses the invariant better than a lint: import-path stability, retired files, endpoint/auth/CSRF contracts, credential absence, removed fake fallbacks, or dispatch cleanup. Write the smallest test, derive canonical routes/keys where practical, run it plus baseline, and retain the proposal's pattern, verification, and follow-on sections.

Phase 4 — Wire into pre-commit + CI

Pre: verify_rule.py passes. Post: .pre-commit-config.yaml has a local hook entry for the rule; .github/workflows/ci.yml has a diff-scoped step that runs the rule on the same file set.

Hook shape. Keep pre-commit broad and put the real rule scope in scripts/lint/run.py so local hooks and CI share the same filter:

  - repo: local
    hooks:
      - id: <rule>
        name: "<rule> (<short rationale>)"
        entry: python3 scripts/lint/run.py --rule <rule>
        language: system
        types: [python]
        files: '^core/.*\.py$'

For non-Python guards, set types and files to the broad staged-file surface for that language, and add a RuleSpec.suffixes entry in scripts/lint/run.py so --staged, --changed-from, and explicit paths all collect the same file types.

CI runs python3 scripts/lint/run.py --changed-from "$BASE" --rule all. When adding a rule, add one RuleSpec in the runner; do not duplicate the scope regex in workflow shell.

Phase 5 — Canonical Patterns entry

Pre: rule wired. Post: .claude/CLAUDE.md has a new bullet under "Canonical Patterns" naming the rule, its intent, and the allow-list shape.

Entry template (one bullet, ≤4 lines):

- **`<rule>` / `scripts/lint/<rule>.py`** — <one-line intent>. The
  allow-list is `<comment> noqa: <rule>: <reason>` (reason required).
  See `tests/lint/<rule>_{bad,good}.<ext>` for the canonical examples.

Match the existing "Canonical Patterns" list's voice — imperative, no emoji.

Phase 6 — Proposal + report

Pre: Phases 1–5 complete. Post: reports/prevent-regression/<id>/proposal.md written, reports/_meta/effectiveness.jsonl appended, user notified.

proposal.md structure:

# Rule proposal: <rule>

## Source cluster
<cluster id + commit ref>

## Pattern
<match shape + path scope + rationale>

## Artifacts
- lint guard: scripts/lint/<rule>.py (new),
  tests/lint/<rule>_{bad,good}.<ext> (new),
  .pre-commit-config.yaml (modified),
  .github/workflows/ci.yml (modified),
  .claude/CLAUDE.md (modified — Canonical Patterns entry)
- test-only guard: focused regression test module(s) plus any
  Canonical Patterns / testing-doc entry needed to explain the
  invariant

## Verification
- `verify_rule.py`: BAD_RC=1 with <N> hits, GOOD_RC=0.
- Historical regression: rule fires on
  `git show <anchor>^:<file>` for each pre-fix site.
- Clean on current HEAD: <list files checked>.

## Follow-on findings
<violations surfaced on other in-scope files that this cluster
did NOT fix — these become new /fix-workflow or /find-dormant
candidates, not Phase 1 work>

Append to reports/_meta/effectiveness.jsonl using the shared scripts/log_effectiveness.py:

python3 scripts/log_effectiveness.py \
  --skill prevent-regression \
  --scan-id "prevent-regression-${TS}" \
  --target "scripts/lint/<rule>.py" \
  --findings-total N \
  --buckets '{"<rule>": N}' \
  --notes "<optional>"

Step 7 — Summarize

Report to the user in ≤10 lines:

• Rule name + AST shape.
• Files created/modified (1 line each).
• Verification results (pass/fail).
• Follow-on findings count (if any).
• Path to proposal.md.
• Next recommended action: human reviews the proposal, installs the staged artifacts and wiring diffs, and commits — or abort if verification failed.

Non-goals

• Fixing pre-existing violations on unrelated files — that's /fix-workflow work, surfaced here as follow-on findings.
• Broadening the rule's AST shape beyond what the source cluster demonstrated — two clusters justify one rule, not a family.
• Running full-repo lint — the rule is diff-scoped by design.

Repository layout

.claude/skills/prevent-regression/
├── SKILL.md                         # this file — orchestrator
├── agents/
│   └── rule-designer.md             # pattern-shape scout brief
├── knowledge/                       # host-overlay slot — ships empty;
│                                    # conventions live in _common/skill-conventions.md
└── scripts/
    ├── generate_rule.py             # rule scaffold generator (Phase 2)
    └── verify_rule.py               # fixture-pair verifier (Phase 3)