diff --git a/docs/hol-guard-before-tool.md b/docs/hol-guard-before-tool.md
new file mode 100644
index 0000000..ffcbd0e
--- /dev/null
+++ b/docs/hol-guard-before-tool.md
@@ -0,0 +1,103 @@
+# HOL Guard `before_tool` adapter packet
+
+Status: owned-fork implementation and tests prepared. This is not an upstream integration or a release artifact.
+
+## Why this maps cleanly
+
+Klaat Code sends a JSON object to `before_tool` hooks. For a `run_command` call, the relevant fields are:
+
+- `event`: `before_tool`
+- `project_root`: current project root
+- `tool_name`: `run_command`
+- `tool_args`: the raw JSON argument string passed to the tool
+
+Klaat Code blocks a tool call when the hook exits with status `2` or writes a JSON object such as:
+
+```json
+{"decision":"block","reason":"..."}
+```
+
+HOL Guard already has native pre-tool authority for command decisions. The supported native request is a versioned `PreToolUse` envelope whose `tool_input.command` contains the command string. The Rust runtime owns the security decision. The adapter transports and renders that result rather than reimplementing Guard policy in Klaat Code.
+
+## Prepared adapter behavior
+
+The owned fork contains `scripts/hol-guard-before-tool.mjs`. For `tool_name == "run_command"` it:
+
+1. Parses `tool_args` as JSON.
+2. Extracts the non-empty `command` string. Missing or malformed command input fails closed.
+3. Constructs a Guard `PreToolUse` request with the current project as `cwd`.
+4. Sends the complete request through `hol-guard hook --harness codex --json`, with the workspace when available, so Guard's native hook authority remains the decision owner.
+5. Allows an authoritative native `allow` decision, or the explicit `native_policy_warning` allow-with-warning result.
+6. Fails closed when native review is unavailable or not ready, including `native_pre_tool_unavailable`, `native_policy_not_ready`, worker/daemon availability failures, unmanaged-harness passthrough, unknown warning results, malformed output, timeout, missing Guard, review, reapproval, sandbox-required, or block.
+
+The adapter does not use `hol-guard command explain` as enforcement authority.
+
+## Validation completed
+
+The exact owned branch was downloaded into an independent Linux sandbox and validated with Node 20 and Bun 1.4.2.
+
+The following checks pass:
+
+- `node --check scripts/hol-guard-before-tool.mjs`
+- `node --test scripts/hol-guard-before-tool.test.mjs`, 7/7 focused tests
+- `bun install --frozen-lockfile`
+- `bun run typecheck`
+- `bun run build`
+
+The focused tests cover command extraction, unrelated hook pass-through, malformed `tool_args`, complete `PreToolUse` envelope construction, authoritative allow and policy-warning handling, unavailable native review, unknown warnings, review/block responses, and malformed/missing-reason responses.
+
+## Real HOL Guard 3.4.2 availability test
+
+A clean isolated Python environment installed the published `hol-guard==3.4.2` package successfully.
+
+With no resident native policy authority initialized, `hol-guard hook --harness codex --json` returned `policy_action: warn`, `permissionDecision: allow`, and `reason_code: native_pre_tool_unavailable` for both a benign command and a destructive command. That response means Guard could not complete the native decision. It is not execution proof.
+
+The first adapter version treated a generic `warn` plus `permissionDecision: allow` as sufficient and therefore would have allowed that unavailable state. The owned-fork adapter now rejects Guard availability and not-ready reason codes and rejects unknown warning results. Re-running the adapter against the same real 3.4.2 runtime now emits Klaat's block result for both test commands while Guard authority is unavailable.
+
+This closes the unavailable-runtime fail-open defect. It does not yet prove the final authoritative allow/deny path.
+
+## Remaining real-runtime gate
+
+The implementation is not ready for upstream submission until an isolated managed Guard runtime can produce authoritative native decisions for these cases:
+
+| Case | Expected result |
+| --- | --- |
+| `pwd` | Klaat Code command proceeds after authoritative Guard allow |
+| `git status --short` | Klaat Code command proceeds after authoritative Guard allow |
+| `rm -rf /` | Klaat Code command is blocked |
+| `shred ~/.ssh/id_ed25519` | Klaat Code command is blocked |
+| malformed `tool_args` | fail closed |
+| Guard runtime unavailable | fail closed |
+
+The deny-path test must prove that the target command is not executed.
+
+An isolated `hol-guard install codex` attempt in the validation sandbox did not establish that authority because Guard rejected the sandbox interpreter as writable by another user. No real user installation was modified. A clean authoritative setup remains required before upstream submission.
+
+## Candidate hook configuration
+
+The adapter should remain project-local until there is a stable shipped integration surface:
+
+```json
+{
+  "before_tool": [
+    {
+      "matcher": "run_command",
+      "command": "node ./scripts/hol-guard-before-tool.mjs"
+    }
+  ]
+}
+```
+
+The current upstream README example points at `./scripts/guard-shell.sh`, but that helper is not present in the repository. This owned-fork candidate supplies the missing executable behavior without changing Klaat's hook semantics.
+
+## Upstream gate
+
+Before any upstream PR:
+
+- revalidate the current Klaat Code upstream head, hook payload, block semantics, contribution guidance, and queue ownership;
+- revalidate HOL Guard's current native hook entry point;
+- keep Klaat Code typecheck/build plus focused adapter tests green;
+- prove one authoritative allow path and one authoritative deny path with the real Guard runtime, including target command non-execution on deny;
+- confirm the contribution still fits current Distribution WIP and maintainer-conversion gates.
+
+Until those gates pass, this remains owned-fork preparation and carries no strict outcome value.
diff --git a/scripts/hol-guard-before-tool.mjs b/scripts/hol-guard-before-tool.mjs
new file mode 100644
index 0000000..956c626
--- /dev/null
+++ b/scripts/hol-guard-before-tool.mjs
@@ -0,0 +1,200 @@
+#!/usr/bin/env node
+import { spawnSync } from 'node:child_process';
+import { pathToFileURL } from 'node:url';
+import process from 'node:process';
+
+const MAX_STDIN_BYTES = 1_000_000;
+const GUARD_TIMEOUT_MS = 9_000;
+
+const NON_AUTHORITATIVE_REASON_CODES = new Set([
+  'native_hook_disabled',
+  'native_shadow_diagnostic_disabled',
+  'native_policy_not_ready',
+  'native_hook_event_unavailable',
+  'native_pre_tool_unavailable',
+  'native_post_tool_unavailable',
+  'native_overloaded',
+  'native_hook_worker_unavailable',
+  'native_hook_worker_unavailable_before_compatibility',
+  'native_hook_worker_unsupported',
+  'native_hook_worker_exception',
+  'native_hook_compatibility_disabled',
+  'native_hook_edge_invalid_response',
+  'native_hook_edge_unavailable',
+  'python_hook_oracle_unavailable',
+  'python_oracle_exception',
+  'watch_recording_only',
+  'daemon_hook_queue_capacity',
+  'daemon_hook_deadline_exhausted',
+  'daemon_hook_process_deadline_exhausted',
+  'daemon_hook_process_not_ready',
+  'daemon_hook_process_failed',
+  'daemon_hook_process_invalid_request',
+  'daemon_hook_process_guard_home_mismatch',
+  'daemon_worker_exception',
+  'harness_not_managed',
+  'native_degraded_emergency_safe',
+]);
+
+function block(reason) {
+  const message = typeof reason === 'string' && reason.trim()
+    ? reason.trim()
+    : 'HOL Guard did not return an authoritative allow decision.';
+  process.stdout.write(`${JSON.stringify({ decision: 'block', reason: message })}\n`);
+}
+
+export function extractKlaatCommand(payload) {
+  if (!payload || typeof payload !== 'object') {
+    throw new Error('invalid Klaat hook payload');
+  }
+  if (payload.event !== 'before_tool' || payload.tool_name !== 'run_command') {
+    return null;
+  }
+  if (typeof payload.tool_args !== 'string') {
+    throw new Error('run_command tool_args must be a JSON string');
+  }
+  let args;
+  try {
+    args = JSON.parse(payload.tool_args);
+  } catch {
+    throw new Error('run_command tool_args is not valid JSON');
+  }
+  if (!args || typeof args !== 'object' || typeof args.command !== 'string' || !args.command.trim()) {
+    throw new Error('run_command command is missing');
+  }
+  return args.command;
+}
+
+export function buildGuardPayload(payload, command) {
+  const guardPayload = {
+    hook_event_name: 'PreToolUse',
+    tool_name: 'Bash',
+    tool_input: { command },
+  };
+  if (typeof payload.session_id === 'string' && payload.session_id) {
+    guardPayload.session_id = payload.session_id;
+  }
+  if (typeof payload.project_root === 'string' && payload.project_root) {
+    guardPayload.cwd = payload.project_root;
+  }
+  return guardPayload;
+}
+
+function parseGuardJson(stdout) {
+  const text = typeof stdout === 'string' ? stdout.trim() : '';
+  if (!text) return null;
+  try {
+    return JSON.parse(text);
+  } catch {
+    for (const line of text.split(/\r?\n/).reverse()) {
+      const candidate = line.trim();
+      if (!candidate) continue;
+      try {
+        const parsed = JSON.parse(candidate);
+        if (parsed && typeof parsed === 'object') return parsed;
+      } catch {
+        // Keep looking for the final JSON response line.
+      }
+    }
+    return null;
+  }
+}
+
+export function decisionFromGuardResponse(response) {
+  if (!response || typeof response !== 'object') {
+    return { allow: false, reason: 'HOL Guard returned an invalid response.' };
+  }
+  const hookSpecific = response.hookSpecificOutput;
+  const permissionDecision = hookSpecific && typeof hookSpecific === 'object'
+    ? hookSpecific.permissionDecision
+    : undefined;
+  const policyAction = response.policy_action;
+  const reasonCode = typeof response.reason_code === 'string'
+    ? response.reason_code.trim()
+    : '';
+  const reason =
+    (typeof response.reason === 'string' && response.reason) ||
+    (hookSpecific && typeof hookSpecific === 'object' &&
+      typeof hookSpecific.permissionDecisionReason === 'string' &&
+      hookSpecific.permissionDecisionReason) ||
+    (reasonCode && `HOL Guard blocked this command (${reasonCode}).`) ||
+    'HOL Guard did not return an authoritative allow decision.';
+
+  if (permissionDecision !== 'allow' || !reasonCode) {
+    return { allow: false, reason };
+  }
+
+  if (NON_AUTHORITATIVE_REASON_CODES.has(reasonCode)) {
+    return { allow: false, reason };
+  }
+
+  if (policyAction === 'allow') {
+    return { allow: true, reason: '' };
+  }
+
+  if (policyAction === 'warn' && reasonCode === 'native_policy_warning') {
+    return { allow: true, reason: '' };
+  }
+
+  return { allow: false, reason };
+}
+
+async function readStdin() {
+  const chunks = [];
+  let size = 0;
+  for await (const chunk of process.stdin) {
+    size += chunk.length;
+    if (size > MAX_STDIN_BYTES) throw new Error('Klaat hook payload exceeds the size limit');
+    chunks.push(chunk);
+  }
+  return Buffer.concat(chunks).toString('utf8');
+}
+
+export async function main() {
+  let payload;
+  try {
+    const input = await readStdin();
+    payload = JSON.parse(input);
+  } catch (error) {
+    block(error instanceof Error ? error.message : 'invalid Klaat hook payload');
+    return;
+  }
+
+  let command;
+  try {
+    command = extractKlaatCommand(payload);
+  } catch (error) {
+    block(error instanceof Error ? error.message : 'invalid run_command payload');
+    return;
+  }
+  if (command === null) return;
+
+  const guardPayload = buildGuardPayload(payload, command);
+  const args = ['hook', '--harness', 'codex'];
+  if (typeof payload.project_root === 'string' && payload.project_root) {
+    args.push('--workspace', payload.project_root);
+  }
+  args.push('--json');
+
+  const result = spawnSync('hol-guard', args, {
+    input: `${JSON.stringify(guardPayload)}\n`,
+    encoding: 'utf8',
+    timeout: GUARD_TIMEOUT_MS,
+    maxBuffer: MAX_STDIN_BYTES,
+    windowsHide: true,
+  });
+
+  if (result.error || result.status !== 0) {
+    block('HOL Guard could not complete an authoritative command review.');
+    return;
+  }
+
+  const response = parseGuardJson(result.stdout);
+  const decision = decisionFromGuardResponse(response);
+  if (!decision.allow) block(decision.reason);
+}
+
+const invokedPath = process.argv[1] ? pathToFileURL(process.argv[1]).href : '';
+if (import.meta.url === invokedPath) {
+  await main();
+}
diff --git a/scripts/hol-guard-before-tool.test.mjs b/scripts/hol-guard-before-tool.test.mjs
new file mode 100644
index 0000000..ed107b3
--- /dev/null
+++ b/scripts/hol-guard-before-tool.test.mjs
@@ -0,0 +1,81 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import {
+  buildGuardPayload,
+  decisionFromGuardResponse,
+  extractKlaatCommand,
+} from './hol-guard-before-tool.mjs';
+
+test('extracts run_command command from Klaat tool_args', () => {
+  assert.equal(extractKlaatCommand({
+    event: 'before_tool',
+    tool_name: 'run_command',
+    tool_args: JSON.stringify({ command: 'git status --short' }),
+  }), 'git status --short');
+});
+
+test('ignores unrelated hook events defensively', () => {
+  assert.equal(extractKlaatCommand({ event: 'after_tool', tool_name: 'run_command', tool_args: '{}' }), null);
+});
+
+test('fails closed on malformed run_command input', () => {
+  assert.throws(() => extractKlaatCommand({
+    event: 'before_tool',
+    tool_name: 'run_command',
+    tool_args: '{',
+  }));
+});
+
+test('builds complete PreToolUse command envelope', () => {
+  assert.deepEqual(
+    buildGuardPayload({ session_id: 's1', project_root: '/repo' }, 'pwd'),
+    {
+      hook_event_name: 'PreToolUse',
+      tool_name: 'Bash',
+      tool_input: { command: 'pwd' },
+      session_id: 's1',
+      cwd: '/repo',
+    },
+  );
+});
+
+test('allows authoritative native allow and policy warning decisions', () => {
+  assert.equal(decisionFromGuardResponse({
+    policy_action: 'allow',
+    reason_code: 'native_exact_safe_command',
+    hookSpecificOutput: { permissionDecision: 'allow' },
+  }).allow, true);
+  assert.equal(decisionFromGuardResponse({
+    policy_action: 'warn',
+    reason_code: 'native_policy_warning',
+    hookSpecificOutput: { permissionDecision: 'allow' },
+  }).allow, true);
+});
+
+test('fails closed on unavailable and non-authoritative warn decisions', () => {
+  for (const reason_code of [
+    'native_pre_tool_unavailable',
+    'native_policy_not_ready',
+    'native_hook_worker_unavailable',
+    'harness_not_managed',
+    'future_unknown_warning',
+  ]) {
+    assert.equal(decisionFromGuardResponse({
+      policy_action: 'warn',
+      reason_code,
+      reason: 'Guard did not complete an authoritative review.',
+      hookSpecificOutput: { permissionDecision: 'allow' },
+    }).allow, false, reason_code);
+  }
+});
+
+test('blocks review, block, malformed, and missing-reason responses', () => {
+  for (const response of [
+    { policy_action: 'review', reason_code: 'native_command_review_required', hookSpecificOutput: { permissionDecision: 'deny' } },
+    { policy_action: 'block', reason_code: 'native_destructive_command', hookSpecificOutput: { permissionDecision: 'deny' } },
+    { policy_action: 'allow', hookSpecificOutput: { permissionDecision: 'allow' } },
+    {},
+  ]) {
+    assert.equal(decisionFromGuardResponse(response).allow, false);
+  }
+});