fix(security): deliver the hook secret to hooks + isolate its rate-limit bucket

Review fixes for COD-54:

- Generated hook curl commands now present X-Codeman-Hook-Secret, read from
  the secret file AT EXECUTION TIME via $CODEMAN_HOOK_SECRET_FILE (exported
  into every managed session's env by tmux buildEnvExports / the direct-PTY
  env builders). Without this, every local hook 401'd the moment a managed
  tunnel came up — the enforcement existed but nothing presented the secret.
  Path-not-value keeps the secret off command lines and out of config files,
  and running sessions pick up a newly generated secret with no respawn;
  server.start() ensures the file exists up front.

- Hook-secret failures now count into a DEDICATED per-IP bucket
  (hookSecretFailures) instead of the shared authFailures map. Legacy
  (pre-secret) hook configs fire constantly from 127.0.0.1; counting their
  401s against the shared bucket would 429 every cookie-less loopback
  request — locking out the Basic-Auth login path (and, through a tunnel,
  every client, since tunneled traffic also arrives as 127.0.0.1).

- docs/security-architecture.md: secret-gated hook exemption, dedicated
  bucket, COD-55 refusal, and the residual caveat for EXTERNAL loopback
  proxies (user-run cloudflared / tailscale serve), which the
  managed-tunnel probe cannot see.

- test/cod54-hook-event-auth.test.ts: +3 tests — login path unaffected
  after hook-bucket exhaustion; generated hooks reference the header +
  $CODEMAN_HOOK_SECRET_FILE without embedding the value; env builders
  export the path only.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/cod54-hook-event-auth.test.ts

@@ -147,4 +147,40 @@ describe('COD-54 hook-event auth — rate limiting', () => {
     }
     expect(saw429).toBe(true);
   });
+
+  it('hook-secret failures do NOT lock out the Basic-Auth login path (separate bucket)', async () => {
+    // The previous test exhausted the hook bucket for 127.0.0.1. Legacy (pre-secret)
+    // hooks fire constantly, so if they shared authFailures, every cookie-less
+    // request from loopback would now 429 — locking out login (and, via a tunnel,
+    // every client). Assert the login path is unaffected:
+    // 1. A credential-less request still gets a 401 challenge, NOT 429.
+    const unauthed = await fetch(`${baseUrl}/api/status`);
+    expect(unauthed.status).toBe(401);
+    // 2. Correct Basic credentials still authenticate.
+    const authed = await fetch(`${baseUrl}/api/status`, {
+      headers: { Authorization: 'Basic ' + Buffer.from(`${TEST_USER}:${TEST_PASS}`).toString('base64') },
+    });
+    expect(authed.status).toBe(200);
+  });
+});
+
+describe('COD-54 secret delivery — generated hooks + session env present the secret', () => {
+  it('generated hook curl commands send the secret header, read from the file at exec time', async () => {
+    const { generateHooksConfig } = await import('../src/hooks-config.js');
+    const config = generateHooksConfig();
+    const commands = JSON.stringify(config);
+    // Header present, value sourced from $CODEMAN_HOOK_SECRET_FILE (not embedded).
+    expect(commands).toContain(HOOK_SECRET_HEADER);
+    expect(commands).toContain('$CODEMAN_HOOK_SECRET_FILE');
+    expect(commands).not.toContain(getHookSecret());
+  });
+
+  it('session env builders export CODEMAN_HOOK_SECRET_FILE (path only, never the value)', async () => {
+    const { buildClaudeEnv, buildShellEnv } = await import('../src/session-cli-builder.js');
+    const claudeEnv = buildClaudeEnv('test-session');
+    const shellEnv = buildShellEnv('test-session');
+    expect(claudeEnv.CODEMAN_HOOK_SECRET_FILE).toMatch(/hook-secret$/);
+    expect(shellEnv.CODEMAN_HOOK_SECRET_FILE).toMatch(/hook-secret$/);
+    expect(JSON.stringify(claudeEnv)).not.toContain(getHookSecret());
+  });
 });