deepseek-harness/packages/hooks/hook-protocol/README.md

# @deepseek-ai/dsh-hook-protocol

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The **shared core** of the Claude Code / Codex hook wire protocol. NOT a cordis plugin — it registers nothing and injects nothing. It is a **library** of dialect-neutral primitives the two bridge plugins (`@deepseek-ai/dsh-hooks-claude`, `@deepseek-ai/dsh-hooks-codex`) import so neither re-implements the identical halves of the protocol.

Why a shared lib at all: Codex deliberately reimplements a *subset* of the Claude Code hook protocol — the same `hooks.json` matcher-group shape, the same exit-code/stdout output contract, the same command-hook execution model. The genuinely-shared parts live here; each bridge owns only what differs.

## What's shared (here) vs. per-dialect (the bridges)

| Concern | Here (`dsh-hook-protocol`) | The bridge (`dsh-hooks-claude` / `-codex`) |
|---|---|---|
| Matcher test | `matchesMatcher(pattern, query, mode)` — literal-or-regex by `mode` | picks its `mode` (`claude` = literal-or-regex, `codex` = always regex) |
| Run a hook | `runHook(bash, hook, opts, now)` — stdin payload + env via `ctx.bash`, decode | builds the per-event stdin **payload** + the dialect's **env** |
| Decode output | `parseHookOutput(exit, stdout, stderr)` → neutral `HookOutput` | maps the neutral `HookOutput` onto a seam-specific typed Decision |
| Merge N hooks | `mergeHookOutputs(outputs)` → most-restrictive `MergedHookOutcome` | — |
| Durable record | `appendHookInvoked` / `appendHookResult` (`hook/*` session events; the result's `decision`/`stderrSummary` derive from the `HookOutput` here) | calls them around each invocation |
| Detached-run quiescence | `createDetachedRuns()` — track fire-and-forget run chains; `drain()` aborts, then awaits them | passes `signal` to each detached `runHook`, registers `drain` as its effect disposer |

## Primitives

- **`matchesMatcher(matcher, query, mode)`** — match-all on absent/`''`/`'*'`; `claude` mode treats a pure `[A-Za-z0-9_|]+` pattern as a literal (pipe = exact-match alternation) and anything else as a regex; `codex` mode is always an unanchored regex. An invalid regex matches nothing (never throws).
- **`runHook(bash, hook, options, now)`** — require and forward the caller-owned `options.signal`, serialize `options.payload` to the hook's stdin (with a trailing newline iff `options.trailingNewline`), merge `options.env` after the executor's credential scrub (the `dsh-bash` trusted-plugin surface), honor the hook's `timeoutSec` (else `options.defaultTimeoutMs` — the bridge owns the default, its config defaulting to the lib's `DEFAULT_HOOK_TIMEOUT_MS` 10-minute reference), and decode the result (threading `options.expectedEventName` to the codec). Cancellation therefore reaches the executor's process-group kill and join boundary. Never throws: an executor rejection (infra fault) becomes a `HookOutput` with `exitCode: undefined` (a non-blocking error). `now` is injected for testable durations.
- **`parseHookOutput(exitCode, stdout, stderr, expectedEventName?)`** decodes exit status and structured stdout. Exit 2 blocks with stderr; other failures are non-blocking. A matching hook-specific permission decision overrides the legacy top-level decision; mismatched or missing event discriminators suppress only event-specific fields. Top-level fields remain event-agnostic, and successful non-JSON output is left to the bridge.
- **`mergeHookOutputs(outputs)`** — fold the results of every hook that matched one point: permission precedence **deny > ask > allow**, halt sticky on the first `continue:false`, block reasons joined with `\n\n`, `additionalContext`/`systemMessages` accumulated in order.
- **`createDetachedRuns()`** — quiescence tracking for the emit-shaped points, which run detached (no seam awaits them). The bridge tracks each run chain — the hook run PLUS its continuation — and registers `drain()` as its effect disposer: drain fires the tracker's abort `signal` (so a still-running hook process is killed via `runHook`, not awaited out to its timeout), then resolves once every tracked chain has settled. `fiber.dispose()` resolving therefore means no detached hook work is left to fire into a disposed context ([defensive patterns](../../../docs/defensive-patterns.md): dispose must reach quiescence).

## `hook/*` session events

Declaration-merged into `SessionEventMap` (log-only, like `compact/*` — NOT a `SurfaceEventType`, no `surfaceOp`): `hook/invoked` (a hook command ran) and `hook/result` (its outcome, paired by `handlerId`, with `appendHookResult` owning the decision rule). Payloads and per-event JSDoc are in the generated [persistence log event catalog](../../../docs/persistence-catalog.md); `stderrSummary` is truncated to the record's `stderrSummaryMaxChars` (the bridge's config, reference default `DEFAULT_STDERR_SUMMARY_MAX_CHARS` = 500; omitted when empty).

Like every event they must sit inside an open turn. The mid-turn points (`PreToolUse`/`PostToolUse`/`UserPromptSubmit`/`Stop`) fire inside the loop's open turn by construction; `SessionStart` gets no `hook/*` record (its injected `user/message` is the durable evidence) — see the hooks Agent Note.

## Model Experience

Indirectly, through `dsh-hooks-claude` and `dsh-hooks-codex`, which can turn parsed hook output into prompt context, blocked outcomes, or continuation feedback.

#### KV Cache effect

No direct invalidation; the named consumer owns any request-prefix changes.

## Known Limitations and Deferred Work

- **`HookOutput.updatedInput` is parsed but not honored** — input rewrite is a deferred consistency-design problem ([the pre-tool-input-rewrite Agent Note](../../../.agents/notes/proposed/feature/2026-06-30-pre-tool-input-rewrite.md)); a bridge logs + warns when a hook sets it. See `src/types.ts` for the full contracts.
- **An invalid matcher regex matches nothing, silently** — `matchesMatcher` never throws; surfacing the error needs a diagnostic-returning variant or parse-time validation (`TODO(matcher-diagnostics)`).