diff --git a/docs/scratchpads/829-mutator-gate.md b/docs/scratchpads/829-mutator-gate.md
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+# WI-2 Scratchpad — Whole mutator-class gate
+
+- **Issue:** Gitea #829
+- **Branch:** `feat/829-mutator-gate`
+- **Base HEAD:** `8ec67a1126adb0dcd4c3a2bf5525f3e239c0b201`
+- **Role:** sol author/build lane only; terra code review and Opus security review are coordinator-owned.
+
+## Mission prompt
+
+Implement BUILD-BRIEF Deliverable 2 as a framework-native whole mutator-class gate under `packages/mosaic/`, building against the merged WI-1 lease broker. No consequential mutator may succeed while UNVERIFIED after a compaction observer fires or after TTL. Carry the T-B compromised-tool acceptance criteria. Enforce revoke-first and promote-last structurally. A receipt is only a promotion prerequisite; the mutator-class gate remains the safety mechanism. M1 is Claude + Pi only.
+
+## Authority verification
+
+Verified exact SHA-256 before design/code:
+
+- BUILD-BRIEF: `89fdbc27ed0e5050dc7b52f3ef2ddaea691edf17fd89d51b15e26fb5ed47171b`
+- SPEC-v5: `a6d07ade835758e8488ca10d3b0631caf0beb93ea3a6733631f151b0c2f01433`
+- Ratification: `bac58319c9c4028b5b40e1129e0033cdb5a6b7b02033c25f06f4cb77d7779c67`
+- sol final red-team: `3da326a4ea91767b731e128a93b13194e8002358101e30de3fcb8ca2f8f54faa`
+
+Carried authority chain also verified/read for the locked T-B gate contract: SPEC-v4 `a5e9c261…`, v4 sol `1e76ee59…`, SPEC-v3 `e0830ba0…`, v3 sol `9f321ade…`.
+
+## Plan
+
+1. RED real-socket acceptance tests for default-deny whole classes, T-B raw-tool bypass, observer/TTL revocation, and structural revoke-first/promote-last.
+2. Extend the merged WI-1 broker as the sole lease authority; authenticate every transition through existing peercred/ancestry/session logic and consume WI-1 single-use cycle tokens atomically before promotion.
+3. Add one broker-backed runtime gate executable and wire it across all Claude `PreToolUse` tools and Pi `tool_call`; unknown/custom tools deny by default.
+4. Add proportional protocol/security/operations documentation and requirements-to-evidence mapping.
+5. Run focused coverage, package/full suites, lint/typecheck/format, then queue-guard, push, open an unmerged PR with `closes #829`, and hand off the exact head.
+
+## Risks and bounds
+
+- Receipt parsing/builders and compaction observers are later WIs; WI-2 exposes the promotion prerequisite boundary but does not treat a receipt as safety authority.
+- Broker restart intentionally loses volatile VERIFIED leases and therefore restarts UNVERIFIED; persistent WI-1 identity/token state remains unchanged.
+- The gate is whole-class and does not parse shell command strings. T-C extension/hook absence and same-UID broker replacement remain outside the client guarantee and server branch protection remains the backstop.
+- Initial lease TTL is capped at ratified 300 seconds; callers may only shorten it.
+- Working budget assumption: 35K tokens; reduce documentation/refactor breadth before touching locked scope if pressure rises.
+
+## Locked discipline
+
+- Re-verify and read the four authority artifacts before design or code.
+- RED-first tests must cover unverified mutation refusal, T-B compromised-tool refusal, and revoke-first/promote-last ordering.
+- Consume WI-1 VERIFIED-lease state; do not re-derive kernel identity, ancestry, sessions, or token authentication.
+- Minimum 85% new-code coverage; full suite, lint, typecheck, and format checks green.
+- Build only: no self-review and no merge. Open a PR containing `closes #829`, report its exact 40-character head, then exit.
diff --git a/packages/mosaic/src/mutator-gate/mutator-gate.acceptance.spec.ts b/packages/mosaic/src/mutator-gate/mutator-gate.acceptance.spec.ts
new file mode 100644
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--- /dev/null
+++ b/packages/mosaic/src/mutator-gate/mutator-gate.acceptance.spec.ts
@@ -0,0 +1,318 @@
+import { chmod, mkdtemp, readFile } from 'node:fs/promises';
+import { createConnection } from 'node:net';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { spawn, spawnSync, type ChildProcess } from 'node:child_process';
+
+import { afterEach, describe, expect, test } from 'vitest';
+
+interface BrokerReply {
+  ok: boolean;
+  code?: string;
+  decision?: 'allow' | 'deny';
+  state?: 'UNVERIFIED' | 'PENDING_VERIFICATION' | 'VERIFIED';
+  session_id?: string;
+  promotion_token?: string;
+}
+
+interface BrokerPaths {
+  socket: string;
+}
+
+const frameworkRoot = new URL('../../framework/', import.meta.url).pathname;
+const daemonPath = join(frameworkRoot, 'tools/lease-broker/daemon.py');
+const gatePath = join(frameworkRoot, 'tools/lease-broker/mutator-gate.py');
+const claudeSettingsPath = join(frameworkRoot, 'runtime/claude/settings.json');
+const piExtensionPath = join(frameworkRoot, 'runtime/pi/mosaic-extension.ts');
+const children: ChildProcess[] = [];
+
+const binding = (compaction_epoch = 1) => ({
+  compaction_epoch,
+  request_epoch: 0,
+  h_source: 'a'.repeat(64),
+  h_payload: 'b'.repeat(64),
+  schema_version: 1,
+});
+
+async function request(socketPath: string, requestValue: object): Promise<BrokerReply> {
+  return await new Promise<BrokerReply>((resolve, reject) => {
+    const socket = createConnection(socketPath);
+    let response = '';
+    socket.setEncoding('utf8');
+    socket.once('error', reject);
+    socket.on('data', (chunk: string) => {
+      response += chunk;
+    });
+    socket.once('end', () => resolve(JSON.parse(response) as BrokerReply));
+    socket.once('connect', () => socket.end(`${JSON.stringify(requestValue)}\n`));
+  });
+}
+
+async function startBroker(): Promise<BrokerPaths> {
+  const root = await mkdtemp(join(tmpdir(), 'mosaic-mutator-gate-'));
+  await chmod(root, 0o700);
+  const socket = join(root, 'broker.sock');
+  const child = spawn(
+    'python3',
+    [daemonPath, '--socket', socket, '--state', join(root, 'state.json')],
+    {
+      stdio: ['ignore', 'pipe', 'pipe'],
+    },
+  );
+  children.push(child);
+  await new Promise<void>((resolve, reject) => {
+    let stderr = '';
+    child.stderr?.setEncoding('utf8');
+    child.stderr?.on('data', (chunk: string) => (stderr += chunk));
+    child.once('error', reject);
+    child.once('exit', (code: number | null) =>
+      reject(new Error(`broker exited ${code}: ${stderr}`)),
+    );
+    child.stdout?.once('data', () => resolve());
+  });
+  return { socket };
+}
+
+async function register(socket: string, runtime_generation = 1): Promise<string> {
+  const reply = await request(socket, { action: 'register_anchor', runtime_generation });
+  expect(reply.ok).toBe(true);
+  expect(reply.session_id).toMatch(/^[a-f0-9]{64}$/);
+  return reply.session_id!;
+}
+
+async function beginVerification(
+  socket: string,
+  session_id: string,
+  runtime: 'claude' | 'pi',
+  runtime_generation = 1,
+  ttl_seconds = 300,
+  compactionEpoch = 1,
+): Promise<BrokerReply> {
+  return await request(socket, {
+    action: 'begin_verification',
+    session_id,
+    runtime_generation,
+    runtime,
+    ttl_seconds,
+    binding: binding(compactionEpoch),
+  });
+}
+
+async function promote(
+  socket: string,
+  session_id: string,
+  promotion_token: string,
+  runtime_generation = 1,
+): Promise<BrokerReply> {
+  return await request(socket, {
+    action: 'promote_lease',
+    session_id,
+    runtime_generation,
+    promotion_token,
+  });
+}
+
+async function authorize(
+  socket: string,
+  session_id: string,
+  runtime: 'claude' | 'pi',
+  tool_name: string,
+  runtime_generation = 1,
+): Promise<BrokerReply> {
+  return await request(socket, {
+    action: 'authorize_tool',
+    session_id,
+    runtime_generation,
+    runtime,
+    tool_name,
+  });
+}
+
+function runRuntimeGate(
+  socket: string,
+  sessionId: string,
+  runtime: 'claude' | 'pi',
+  toolName: string,
+  generation = 1,
+) {
+  return spawnSync('python3', [gatePath, '--runtime', runtime], {
+    input: `${JSON.stringify({ tool_name: toolName })}\n`,
+    encoding: 'utf8',
+    env: {
+      ...process.env,
+      MOSAIC_LEASE_BROKER_SOCKET: socket,
+      MOSAIC_LEASE_SESSION_ID: sessionId,
+      MOSAIC_RUNTIME_GENERATION: String(generation),
+    },
+  });
+}
+
+afterEach(() => {
+  for (const child of children.splice(0)) child.kill('SIGTERM');
+});
+
+describe('whole mutator-class lease gate', () => {
+  test('revoke-first and promote-last structurally bracket mutator authority', async () => {
+    const { socket } = await startBroker();
+    const sessionId = await register(socket);
+
+    expect(await promote(socket, sessionId, 'c'.repeat(64))).toMatchObject({
+      ok: false,
+      code: 'INVALID_LEASE_TRANSITION',
+    });
+    expect(await authorize(socket, sessionId, 'claude', 'Bash')).toMatchObject({
+      ok: false,
+      code: 'MUTATOR_UNVERIFIED',
+      decision: 'deny',
+    });
+
+    const pending = await beginVerification(socket, sessionId, 'claude');
+    expect(pending).toMatchObject({ ok: true, state: 'PENDING_VERIFICATION' });
+    expect(pending.promotion_token).toMatch(/^[a-f0-9]{64}$/);
+    expect(await authorize(socket, sessionId, 'claude', 'Write')).toMatchObject({
+      ok: false,
+      decision: 'deny',
+    });
+
+    expect(await promote(socket, sessionId, pending.promotion_token!)).toMatchObject({
+      ok: true,
+      state: 'VERIFIED',
+    });
+    expect(await authorize(socket, sessionId, 'claude', 'Bash')).toMatchObject({
+      ok: true,
+      decision: 'allow',
+      state: 'VERIFIED',
+    });
+
+    const nextCycle = await beginVerification(socket, sessionId, 'claude', 1, 300, 2);
+    expect(nextCycle).toMatchObject({ ok: true, state: 'PENDING_VERIFICATION' });
+    expect(await authorize(socket, sessionId, 'claude', 'Edit')).toMatchObject({
+      ok: false,
+      decision: 'deny',
+    });
+    expect(await promote(socket, sessionId, pending.promotion_token!)).toMatchObject({
+      ok: false,
+      code: 'PROMOTION_TOKEN_MISMATCH',
+    });
+  });
+
+  test('T-B raw and custom mutator tools are default-denied without shell parsing', async () => {
+    const { socket } = await startBroker();
+    const sessionId = await register(socket);
+    const mutators: Array<['claude' | 'pi', string]> = [
+      ['claude', 'Bash'],
+      ['claude', 'Edit'],
+      ['claude', 'Write'],
+      ['claude', 'NotebookEdit'],
+      ['claude', 'mcp__provider__close_issue'],
+      ['pi', 'bash'],
+      ['pi', 'edit'],
+      ['pi', 'write'],
+      ['pi', 'deploy'],
+      ['pi', 'unknown_custom_tool'],
+    ];
+
+    for (const [runtime, toolName] of mutators) {
+      expect(
+        await authorize(socket, sessionId, runtime, toolName),
+        `${runtime}:${toolName}`,
+      ).toMatchObject({
+        ok: false,
+        code: 'MUTATOR_UNVERIFIED',
+        decision: 'deny',
+      });
+    }
+
+    for (const [runtime, toolName] of [
+      ['claude', 'Read'],
+      ['claude', 'Grep'],
+      ['pi', 'read'],
+      ['pi', 'grep'],
+      ['pi', 'mosaic_context_recover'],
+    ] as const) {
+      expect(await authorize(socket, sessionId, runtime, toolName)).toMatchObject({
+        ok: true,
+        decision: 'allow',
+      });
+    }
+  });
+
+  test('observer revocation and monotonic TTL expiry deny the next mutator', async () => {
+    const { socket } = await startBroker();
+    const sessionId = await register(socket);
+    const pending = await beginVerification(socket, sessionId, 'claude', 1, 1);
+    await promote(socket, sessionId, pending.promotion_token!);
+
+    expect(await authorize(socket, sessionId, 'claude', 'Bash')).toMatchObject({
+      ok: true,
+      decision: 'allow',
+    });
+    await new Promise((resolve) => setTimeout(resolve, 1_100));
+    expect(await authorize(socket, sessionId, 'claude', 'Bash')).toMatchObject({
+      ok: false,
+      code: 'LEASE_EXPIRED',
+      decision: 'deny',
+    });
+
+    const refreshed = await beginVerification(socket, sessionId, 'claude', 1, 300, 2);
+    await promote(socket, sessionId, refreshed.promotion_token!);
+    expect(
+      await request(socket, {
+        action: 'revoke_lease',
+        session_id: sessionId,
+        runtime_generation: 1,
+        reason: 'compaction_observer',
+      }),
+    ).toMatchObject({ ok: true, state: 'UNVERIFIED' });
+    expect(await authorize(socket, sessionId, 'claude', 'Write')).toMatchObject({
+      ok: false,
+      code: 'MUTATOR_UNVERIFIED',
+      decision: 'deny',
+    });
+  });
+
+  test('runtime-generation replacement cannot inherit a verified lease', async () => {
+    const { socket } = await startBroker();
+    const sessionId = await register(socket);
+    const pending = await beginVerification(socket, sessionId, 'pi');
+    await promote(socket, sessionId, pending.promotion_token!);
+
+    expect(await authorize(socket, sessionId, 'pi', 'bash', 2)).toMatchObject({
+      ok: false,
+      code: 'MUTATOR_UNVERIFIED',
+      decision: 'deny',
+    });
+    expect(await authorize(socket, sessionId, 'pi', 'bash', 1)).toMatchObject({
+      ok: false,
+      code: 'STALE_GENERATION',
+    });
+  });
+
+  test('Claude and Pi runtime adapters consult the broker for every tool class', async () => {
+    const { socket } = await startBroker();
+    const sessionId = await register(socket);
+
+    expect(runRuntimeGate(socket, sessionId, 'claude', 'Read').status).toBe(0);
+    expect(runRuntimeGate(socket, sessionId, 'claude', 'Bash').status).toBe(2);
+    expect(runRuntimeGate(socket, sessionId, 'pi', 'unknown_custom_tool').status).toBe(2);
+
+    const pending = await beginVerification(socket, sessionId, 'claude');
+    await promote(socket, sessionId, pending.promotion_token!);
+    expect(runRuntimeGate(socket, sessionId, 'claude', 'Bash').status).toBe(0);
+
+    const settings = JSON.parse(await readFile(claudeSettingsPath, 'utf8')) as {
+      hooks: { PreToolUse: Array<{ matcher?: string; hooks: Array<{ command: string }> }> };
+    };
+    expect(
+      settings.hooks.PreToolUse.some(
+        (entry) =>
+          entry.matcher === '.*' &&
+          entry.hooks.some((hook) => hook.command.includes('mutator-gate.py')),
+      ),
+    ).toBe(true);
+
+    const piExtension = await readFile(piExtensionPath, 'utf8');
+    expect(piExtension).toContain("pi.on('tool_call'");
+    expect(piExtension).toContain('mutator-gate.py');
+  });
+});