diff --git a/.github/workflows/seatbelt-system-keychains.yml b/.github/workflows/seatbelt-system-keychains.yml
new file mode 100644
index 0000000000..b28a089f06
--- /dev/null
+++ b/.github/workflows/seatbelt-system-keychains.yml
@@ -0,0 +1,42 @@
+name: Seatbelt system Keychains smoke
+
+on:
+  pull_request:
+    paths:
+      - 'cli/src/lib/sandbox/seatbelt.js'
+      - 'cli/__tests__/seatbelt.system-keychains.smoke.test.mjs'
+      - 'cli/__tests__/seatbelt.claude-keychain-read.smoke.test.mjs'
+      - '.github/workflows/seatbelt-system-keychains.yml'
+
+permissions:
+  contents: read
+
+jobs:
+  adapter-turns:
+    runs-on: macos-15
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+          cache: npm
+          cache-dependency-path: cli/package-lock.json
+      - run: npm ci --prefix cli
+      - name: Install tested OpenCode for a disposable adapter turn
+        run: npm install --prefix "$RUNNER_TEMP/opencode-smoke" opencode-ai@1.19.0
+      - name: Exercise system Keychains denials and real adapter turns
+        env:
+          COMMONLY_OPENCODE_SMOKE_BINARY: ${{ runner.temp }}/opencode-smoke/node_modules/.bin/opencode
+          # Writes a probe item into this disposable runner's login keychain.
+          COMMONLY_KEYCHAIN_PROBE: '1'
+        run: |
+          cd cli
+          node --experimental-vm-modules node_modules/.bin/jest \
+            __tests__/seatbelt.system-keychains.smoke.test.mjs \
+            __tests__/seatbelt.claude-keychain-read.smoke.test.mjs \
+            __tests__/adapters.opencode.seatbelt.smoke.test.mjs \
+            __tests__/adapters.qwen.seatbelt.smoke.test.mjs \
+            __tests__/seatbelt.claude-runtime.smoke.test.mjs \
+            --runInBand --testTimeout=60000
diff --git a/cli/__tests__/seatbelt.claude-keychain-read.smoke.test.mjs b/cli/__tests__/seatbelt.claude-keychain-read.smoke.test.mjs
new file mode 100644
index 0000000000..2127abce54
--- /dev/null
+++ b/cli/__tests__/seatbelt.claude-keychain-read.smoke.test.mjs
@@ -0,0 +1,77 @@
+import { spawnSync } from 'child_process';
+import { mkdirSync, mkdtempSync, rmSync } from 'fs';
+import { homedir, tmpdir } from 'os';
+import { join } from 'path';
+import { randomBytes } from 'crypto';
+import { buildSeatbeltProfile } from '../src/lib/sandbox/seatbelt.js';
+
+/**
+ * Does Claude's credential read survive the removal of the system Keychains
+ * folder from the baseline? Claude reads its OAuth item by running
+ * /usr/bin/security, whose default search list includes System.keychain.
+ * If Security.framework treats a denied search-list keychain as fatal, every
+ * public Claude seat would fail to log in after the change ships (TASK-233,
+ * Otto's Ask 2 on eca2d8d79).
+ *
+ * This writes a probe item into the login keychain, so it runs only when the
+ * disposable macOS job sets COMMONLY_KEYCHAIN_PROBE=1. It never runs on an
+ * operator host.
+ */
+const probeEnabled = process.platform === 'darwin' && process.env.COMMONLY_KEYCHAIN_PROBE === '1';
+const macProbe = probeEnabled ? test : test.skip;
+
+const SERVICE = 'commonly-seatbelt-probe';
+const loginKeychain = join(homedir(), 'Library', 'Keychains', 'login.keychain-db');
+const secret = randomBytes(16).toString('hex');
+const root = probeEnabled ? mkdtempSync(join(tmpdir(), 'commonly-keychain-probe-')) : null;
+const workspace = root && join(root, 'workspace');
+const state = root && join(root, 'state');
+if (root) {
+  mkdirSync(workspace);
+  mkdirSync(state);
+}
+
+beforeAll(() => {
+  if (!probeEnabled) return;
+  const added = spawnSync('/usr/bin/security', [
+    'add-generic-password', '-U', '-s', SERVICE, '-a', 'commonly', '-w', secret, loginKeychain,
+  ], { encoding: 'utf8' });
+  if (added.status !== 0) throw new Error(`could not write the probe item: ${added.stderr}`);
+});
+
+afterAll(() => {
+  if (!probeEnabled) return;
+  spawnSync('/usr/bin/security', ['delete-generic-password', '-s', SERVICE, loginKeychain], { encoding: 'utf8' });
+  rmSync(root, { recursive: true, force: true });
+});
+
+// A confined Node spawns security, as the Claude CLI does. The profile is the
+// Claude runtime profile, or that profile plus one extra rule for a control.
+const readProbe = (extraRules = '') => {
+  const profile = `${buildSeatbeltProfile({
+    workspacePath: workspace, executablePath: process.execPath, statePath: state, allowClaudeRuntimeAccess: true,
+  })}\n${extraRules}`;
+  return spawnSync('/usr/bin/sandbox-exec', [
+    '-p', profile, process.execPath, '-e',
+    `const { spawnSync } = require('child_process');
+     const r = spawnSync('/usr/bin/security', ['find-generic-password', '-s', '${SERVICE}', '-w'], { encoding: 'utf8' });
+     process.stdout.write(String(r.stdout).trim()); process.stderr.write(String(r.stderr).trim()); process.exitCode = r.status;`,
+  ], { cwd: workspace, encoding: 'utf8', timeout: 20_000 });
+};
+
+macProbe('the probe item is readable outside any sandbox (precondition)', () => {
+  const result = spawnSync('/usr/bin/security', ['find-generic-password', '-s', SERVICE, '-w'], { encoding: 'utf8' });
+  expect({ status: result.status, stdout: result.stdout.trim() }).toEqual({ status: 0, stdout: secret });
+});
+
+macProbe('the Claude runtime profile still reads its credential with System.keychain denied', () => {
+  const result = readProbe();
+  expect({ status: result.status, stdout: result.stdout, stderr: result.stderr }).toEqual({
+    status: 0, stdout: secret, stderr: '',
+  });
+});
+
+macProbe('control: the old broad Keychains folder grant also reads it', () => {
+  const result = readProbe('(allow file-read* (subpath "/Library/Keychains"))');
+  expect({ status: result.status, stdout: result.stdout }).toEqual({ status: 0, stdout: secret });
+});
diff --git a/cli/__tests__/seatbelt.system-keychains.smoke.test.mjs b/cli/__tests__/seatbelt.system-keychains.smoke.test.mjs
new file mode 100644
index 0000000000..8dfc35440c
--- /dev/null
+++ b/cli/__tests__/seatbelt.system-keychains.smoke.test.mjs
@@ -0,0 +1,68 @@
+import { spawnSync } from 'child_process';
+import { mkdirSync, mkdtempSync, rmSync } from 'fs';
+import { homedir } from 'os';
+import { join } from 'path';
+import { buildSeatbeltProfile } from '../src/lib/sandbox/seatbelt.js';
+
+const macTest = process.platform === 'darwin' ? test : test.skip;
+const root = process.platform === 'darwin'
+  ? mkdtempSync(join(homedir(), '.commonly-keychain-smoke-')) : null;
+const workspace = root && join(root, 'workspace');
+const state = root && join(root, 'state');
+if (root) {
+  mkdirSync(workspace);
+  mkdirSync(state);
+}
+afterAll(() => { if (root) rmSync(root, { recursive: true, force: true }); });
+
+// Two profiles reach the Keychain, and only the Claude one passes this flag.
+// The denial must hold under both, or a grant added to claudeRuntimeRules
+// would go unnoticed (TASK-233, Otto's mutation on eca2d8d79).
+const PROFILES = [
+  { label: 'public', options: {} },
+  { label: 'Claude runtime', options: { allowClaudeRuntimeAccess: true } },
+];
+
+const run = (code, options = {}) => spawnSync('/usr/bin/sandbox-exec', [
+  '-p', buildSeatbeltProfile({
+    workspacePath: workspace, executablePath: process.execPath, statePath: state, ...options,
+  }), process.execPath, '-e', code,
+], {
+  cwd: workspace, encoding: 'utf8', timeout: 15_000,
+});
+
+describe.each(PROFILES)('$label Seatbelt', ({ options }) => {
+  macTest('denies listing and opening system Keychains', () => {
+    const result = run(`const fs = require('fs');
+      for (const path of ['/Library/Keychains', '/Library/Keychains/System.keychain',
+        '/Library/Keychains/apsd.keychain']) {
+        try {
+          if (path.endsWith('/Keychains')) fs.readdirSync(path);
+          else fs.closeSync(fs.openSync(path, 'r'));
+          console.log('ALLOWED');
+        } catch (error) { console.log(error.code); }
+      }`, options);
+    expect(result.error).toBeUndefined();
+    expect({ status: result.status, stderr: result.stderr }).toEqual({ status: 0, stderr: '' });
+    expect(result.stdout.trim().split('\n')).toEqual(['EPERM', 'EPERM', 'EPERM']);
+  });
+
+  // Node reads this file at startup with no OPENSSL_CONF override, so the
+  // literal grant in PLATFORM_BASELINE must let the read through (TASK-233).
+  macTest('reads the system OpenSSL config that Node loads at startup', () => {
+    const result = run(`const fs = require('fs');
+      try { fs.readFileSync('/System/Library/OpenSSL/openssl.cnf'); console.log('READ'); }
+      catch (error) { console.log(error.code); }`, options);
+    expect(result.error).toBeUndefined();
+    expect(result.stdout.trim()).toBe('READ');
+  });
+});
+
+macTest('Node can complete HTTPS with the system Keychains folder denied', () => {
+  const result = run(`fetch('https://example.com')
+    .then((response) => { console.log(response.status); })
+    .catch((error) => { console.error(error.message); process.exitCode = 1; });`);
+  expect(result.error).toBeUndefined();
+  expect({ status: result.status, stdout: result.stdout.trim(), stderr: result.stderr })
+    .toEqual({ status: 0, stdout: '200', stderr: '' });
+});
diff --git a/cli/src/lib/sandbox/seatbelt.js b/cli/src/lib/sandbox/seatbelt.js
index 33419115ea..d0cbbee421 100644
--- a/cli/src/lib/sandbox/seatbelt.js
+++ b/cli/src/lib/sandbox/seatbelt.js
@@ -45,7 +45,8 @@ const PLATFORM_BASELINE = String.raw`
     (path "/dev/null")
     (vnode-type CHARACTER-DEVICE)))
 
-; Loader + standard system resources.
+; Loader + standard system resources. Node opens this one macOS OpenSSL config
+; file at startup; the macOS adapter job's Node was denied it without this rule.
 (allow file-read* file-test-existence
   (subpath "/Library/Apple")
   (subpath "/Library/Filesystems/NetFSPlugins")
@@ -54,8 +55,8 @@ const PLATFORM_BASELINE = String.raw`
   (subpath "/private/var/db/timezone")
   (subpath "/usr/lib")
   (subpath "/usr/share")
+  (literal "/System/Library/OpenSSL/openssl.cnf")
   (subpath "/Library/Preferences")
-  (subpath "/Library/Keychains")
   (subpath "/var/db")
   (subpath "/private/var/db"))
 (allow file-read* file-test-existence