coding-agents-hooks-authoring-456c45— agent skill

<hooks_authoring>

Hook entry rule

Only files that export defineHook(…) AND call runAsCli(hook, module) belong directly in src/hooks/src/hooks/. Every .ts at the top level of that directory becomes a standalone CJS bundle distributed to all 5 IDEs (claude, codex, copilot, cursor, windsurf). Helper/data files without runAsCli belong in a named subdirectory: src/hooks/src/hooks/<feature>/.

Helper placement

• Feature-local helpers → src/hooks/src/hooks/<feature>/ (e.g. src/hooks/src/hooks/dangerous-actions/patterns.ts).
• Cross-hook runtime helpers → src/hooks/src/runtime/.

Build is non-recursive

src/hooks/scripts/build-bundles.mjs:24 uses readdirSync(hooksDir).filter(f => f.endsWith('.ts')). There is no `{ recursive: true }`. Subdirectories are invisible to the bundler. Adding a top-level .ts without runAsCli produces a dead bundle for all 5 IDEs.

Adding a SemanticKind

When a hook needs a new tool category (e.g. mcp-call):

1. `src/hooks/src/runtime/ide-registry.ts` — add a row to TOOL_KINDS with all 5 IDE columns (null where the event doesn't exist). SemanticKind = keyof typeof TOOL_KINDS so TypeScript enforces coverage.
2. `src/hooks/src/runtime/ide-rows/<ide>.ts` — if the kind requires special logic (e.g. prefix-match for mcp__.*), add a conditional branch at the top of lookupToolKind in the IDE-row file before the table loop. Table-driven lookup alone cannot handle open-ended tool name patterns.
3. Hook entry — add the new kind to def.on.toolKinds.
4. Matcher in `hooks.json.tmpl` — widen to include new tool names/patterns.

Order matters: run-hook.ts:98 gates on toolKinds before calling run(ctx). Matcher passes the event in; toolKinds must include the mapped kind or the call is dropped silently.

Registration

Every new hook must appear in every plugin's hooks.json. The canonical source is plugins/core-claude/hooks/hooks.json.tmpl (and equivalent templates in other plugins). Direct edits to generated hooks.json files are overwritten on the next npx rosettify-plugins@latest run.

Paths by plugin:

• plugins/core-claude/hooks/hooks.json.tmpl → hooks.json
• plugins/core-copilot/hooks/hooks.json.tmpl → hooks/hooks.json
• plugins/core-cursor/.cursor/hooks/hooks.json.tmpl → hooks.json
• plugins/core-codex/.codex/hooks/hooks.json.tmpl → hooks.json
• plugins/core-windsurf/ — bundles are distributed but hooks.json registration is not covered by the regression test (hooks-registered.test.ts); register manually if needed.

Platform-scoped events

PreToolUse is absent on Copilot ('copilot': null in ide-registry.ts). If a hook uses a platform-exclusive event, add its name to CLAUDE_CODE_ONLY_HOOKS Set in src/hooks/tests/regression/hooks-registered.test.ts. Before adding a second scoped hook, refactor the Set to Map<string, Set<IdeName>>.

Tests

Co-locate tests in src/hooks/tests/<hook-name>.test.ts. The regression test (src/hooks/tests/regression/hooks-registered.test.ts) automatically discovers all .ts entries at src/hooks/src/hooks/ top level and asserts each is referenced in every plugin's hooks.json. A new hook without registration immediately fails the regression guard.

Sync command

After any source change under src/hooks/src/ or instructions/r{2,3}/core/:

venv/bin/python scripts/pre_commit.py

This builds CJS bundles, runs full test suite, and runs npx rosettify-plugins@latest to sync instructions/r{2,3}/core/ → all plugin directories.

Pitfalls

• Helper files in top-level — produces dead bundles for all 5 IDEs + false regression test failures without isLibraryModule workaround. Fix: move to subdirectory.
• Missing registration — hook fires silently nowhere; regression test catches this at CI time.
• Secrets in Evidence — buildDenyMessage echoes evidence to transcript by default. Pass redact=true for DANGEROUS_CONTENT matches (AWS keys, PEM certs, SQL with row data).
• Regex `[rf]{2,}` false positives — matches rm -rr and rm -ff. Require both flags with lookaheads: /\brm\s+-(?=[a-zA-Z]*[rR])(?=[a-zA-Z]*[fF])[a-zA-Z]+\b/.
• `$`-anchor vs trailing slash — path patterns like /\.kube\/config$ fail when tested against filePath with trailing slash. Always test against normalizedPath = filePath.replace(/\/+$/, '').
• Matcher without toolKinds mapping — adding a name to the JSON matcher but not to lookupToolKind and def.on.toolKinds is inert.

Reference files

src/hooks/scripts/build-bundles.mjs
src/hooks/src/runtime/ide-registry.ts
src/hooks/src/runtime/ide-rows/claude-code.ts
src/hooks/src/runtime/run-hook.ts:98
plugins/core-claude/hooks/hooks.json.tmpl
src/hooks/tests/regression/hooks-registered.test.ts

</hooks_authoring>