# Working in `hooks/` This directory is wiring, not logic. Two files: `hooks.json` registers the events, `run.mjs` is the one entry point every hook and the MCP server go through. The behaviour lives in TypeScript under `mcp/src/hooks/` and ships compiled as `dist/hooks/.js`. Editing a hook almost always means editing `mcp/src/hooks/`, not here. ## `run.mjs` is the launcher `.sh` hooks are unreliable on Windows, so every entry in `hooks.json` — and `.mcp.json` — is `"command": "node"` with `["${CLAUDE_PLUGIN_ROOT}/hooks/run.mjs", ""]`: `node.exe` is a real executable and needs no shell. Keep that shape; `mcp/test/packaging.test.ts` asserts the server entry is exactly that string. `run.mjs` maps `` to `dist/hooks/.js` (`server` → `dist/server.js`) and resolves it, most specific first: `EKLAVYA_RUNTIME`, then the checkout's own `mcp/dist` (only when `mcp/node_modules/better-sqlite3` exists), then `~/.eklavya/runtime/node_modules/eklavya`. In a development checkout your local build wins — so rebuild before you test. With no build reachable, `server` falls back to `npx eklavya@ serve` and a hook starts a detached background `npm install` (once an hour at most, claimed by a `.installing` stamp before spawning) and exits 0 saying nothing. **It carries no version number.** It reads `.claude-plugin/plugin.json` at runtime, and `mcp/test/packaging.test.ts` asserts the file matches no `\d+\.\d+\.\d+` anywhere and does match `plugin\.json` — so writing any dotted triple in here, even in a comment, fails that test on purpose. `scripts/bump-version.sh` bumps `plugin.json` and `mcp/package.json`, nothing else. ## The five hooks, out of `hooks.json` | Event | Matcher | Timeout | Script | Job | |---|---|---|---|---| | SessionStart | — | 10s | `session-start` | stamp `meta.current_session`, print the profile banner and the standing log directive | | UserPromptSubmit | — | 10s | `prompt-submit-nudge` | re-state the log directive in one line, but only for a session that has logged nothing after a grace window | | PreToolUse | `Bash` | 10s | `pre-tool-gate` | in `enforced` mode only, deny a `git commit` whose session gate has not passed | | PostToolUse | `mcp__.*log_session_concepts` | 10s | `checkpoint-quiz` | one mid-task question, `interleaved` cadence only | | Stop | — | 15s | `stop-quiz-check` | block the turn and demand a quiz | The PostToolUse matcher is a regex over the MCP tool name, not a literal, because the prefix depends on how the plugin was installed — `mcp__eklavya__log_session_concepts` standalone, `mcp__plugin_eklavya_eklavya__log_session_concepts` via `/plugin`. `mcp__.*` catches both; anchoring it to one spelling silently disables the checkpoint for half the installs. ## Every failure path exits 0 A hook that throws breaks the user's session, and a learning tool that breaks sessions gets uninstalled. `run()` in `mcp/src/hooks/lib.ts` enforces it: parse stdin defensively, run the body, exit 0 silently on any throw. A new hook body goes inside `await run(async (input) => { ... })` and returns an exit code; it never calls `process.exit` itself. Helpers follow the same rule — `openExisting()` returns `null` rather than throwing on a missing or corrupt database, and deliberately does not migrate or seed (several hooks racing a migration on session start is a corruption story). The one non-zero code is the Stop hook's `return 2`, which is how Stop blocks; the reason goes on stderr. ## A hook must never *wait*, either Exiting 0 on a throw covers the loud failure. The quiet one is worse: a hook that blocks never errors, never logs, and stalls the session on every tool call that triggers it — with nothing for the developer to report except that Claude Code got slow. It is reachable. `readInput` used to be `for await (const chunk of process.stdin)`, which has exactly one exit: EOF. On Windows the host may run a hook through a PowerShell block that swallows the piped JSON, so `end` never fires (reported by ponytail, #443). `run.mjs` is careful about everything else — Node version, four resolution candidates, a self-expiring heal claim, exit 0 on every throw — and this was the one gap. `mcp/src/stdin.ts` closes it, and `eklavya statusline` shares it: both read a JSON blob the host pipes in, both must degrade rather than hang, and two copies would be one copy getting the fix. Three things matter about it. **The bound is on silence, not on total time.** A flat cap truncates a payload still arriving when it fires, and truncated JSON does not fail loudly — it fails as `{}`, so the hook runs to completion having quietly decided the session has no cwd and no id. The idle timer resets on every chunk, so a slow or large payload is never cut off; a total cap sits behind it for a stream that never stops. **Every timer is `unref`'d.** `end` arrives first in almost every real invocation, and a pending timer must not hold the process open or add latency to a hook that has already done its work. **There is an `error` handler.** A stream that errors never emits `end`, so without one the read waits on something that is not coming. `HOOK_STDIN` is 2s idle / 5s total, well under the 10s `hooks.json` grants (15 for Stop) — a read that outlives its host timeout is a read the developer waits on, and `test/stdin.test.ts` asserts the relationship rather than the number. That suite spawns a real hook, writes a payload, and **never closes stdin**; against the old code all three cases hang until the test kills them. `stripBom` runs before every `JSON.parse` here. Some Windows shells prepend a byte-order mark, and `JSON.parse` throws on input that looks perfectly well-formed in a terminal and in any editor — another silent nothing-happens. ## The Stop hook blocks in `ambient` too Commonly got wrong. `ambient` is not "never interrupts" — `stop-quiz-check.ts` returns 2 in ambient as readily as in enforced. `enforced` changes three things: the `min_minutes_between_quizzes` cooldown is skipped (a cooldown could make a commit gate unpassable — decision G5); the one-question cap under `interleaved` is lifted, so the sweep asks for the whole remaining budget; and `pre-tool-gate` plus `cli/eklavya-gate` start holding commits. Only `mode === 'off'` silences everything. ## The loop guard A Stop hook that blocks on every Stop blocks forever, and `stop_hook_active` is no longer a documented input. So the rule is: block only when the count of `origin = 'work'` rows in `session_concepts` has **grown** since the last block. Blocking stamps that count into `stop_markers` (`last_logged_count`, `last_blocked_at`, `block_count`), *before* the block — a failure after it costs a missed quiz, never a loop. `max_stop_blocks_per_session` (default 3) caps even genuinely new work. Counting review-origin rows here would let answering a question re-arm the block that asked it; don't. `checkpoint-quiz.ts` has the mirror-image guard for mid-turn bursts, stamping `checkpoints` before it emits. ## Pacing Two different keys, one hook each (`mcp/src/config.ts` is the source of truth): `min_minutes_between_checkpoints` (default 4) paces the single mid-task question and is read by `checkpoint-quiz.ts`, against both the last checkpoint and the last answer; `min_minutes_between_quizzes` (default 20) paces a whole Stop quiz, is read by `stop-quiz-check.ts`, and applies **in `ambient` only**. `max_questions_per_task` (default 4) is a session allowance shared by both hooks: every `attempts` row spends it, so the Stop hook asks for whatever the checkpoints left. The two hooks' candidate queries share a WHERE clause verbatim; if you change one, change both, or a concept gets asked twice or never. ## The SessionStart banner is a format string The `[Eklavya] ...` line in `mcp/src/hooks/session-start.ts` is quoted verbatim by `web/public/index.html` (the hero terminal script) and `web/src/content/docs/docs/installing.mdx` (the no-history variant). Changing its wording, order or fields means re-quoting both in the same commit. ## Testing a hook by hand `dist/` must exist first — the tests run the built files, not the sources, and `pretest` builds them. From `mcp/`: ```sh npm run build echo '{"session_id":"s1","cwd":"/path/to/repo","hook_event_name":"Stop"}' \ | EKLAVYA_DB=/tmp/k.db EKLAVYA_HOME=/tmp/eklavya-home \ node dist/hooks/stop-quiz-check.js; echo "exit $?" ``` `EKLAVYA_DB` and `EKLAVYA_HOME` point a hook at a scratch database and config; `EKLAVYA_SESSION_ID` overrides the harness session id. `mcp/test/hooks.test.ts` and `mcp/test/gate.test.ts` do exactly this.