diff --git a/src/resources/extensions/gsd/tests/post-mutation-hook.test.ts b/src/resources/extensions/gsd/tests/post-mutation-hook.test.ts
new file mode 100644
index 000000000..929c62dad
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/post-mutation-hook.test.ts
@@ -0,0 +1,171 @@
+// GSD Extension — post-mutation hook regression tests
+// Verifies that after a successful handleCompleteTask call, the post-mutation
+// hook fires: event-log.jsonl and state-manifest.json are both written.
+
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import * as os from 'node:os';
+import { openDatabase, closeDatabase } from '../gsd-db.ts';
+import { handleCompleteTask } from '../tools/complete-task.ts';
+import { readEvents } from '../workflow-events.ts';
+import { readManifest } from '../workflow-manifest.ts';
+
+function tempDir(): string {
+  return fs.mkdtempSync(path.join(os.tmpdir(), 'gsd-post-hook-'));
+}
+
+function cleanupDir(dirPath: string): void {
+  try { fs.rmSync(dirPath, { recursive: true, force: true }); } catch { /* best effort */ }
+}
+
+/** Create a minimal project directory with a PLAN.md for complete-task to find. */
+function createProject(basePath: string): void {
+  const sliceDir = path.join(basePath, '.gsd', 'milestones', 'M001', 'slices', 'S01');
+  const tasksDir = path.join(sliceDir, 'tasks');
+  fs.mkdirSync(tasksDir, { recursive: true });
+  fs.writeFileSync(path.join(sliceDir, 'S01-PLAN.md'), `# S01: Test Slice
+
+## Tasks
+
+- [ ] **T01: Test task** \`est:30m\`
+  - Do: Implement the thing
+  - Verify: Run tests
+
+- [ ] **T02: Second task** \`est:1h\`
+  - Do: Implement more
+  - Verify: Run more tests
+`);
+}
+
+function makeCompleteTaskParams() {
+  return {
+    taskId: 'T01',
+    sliceId: 'S01',
+    milestoneId: 'M001',
+    oneLiner: 'Implemented auth middleware',
+    narrative: 'Added JWT validation middleware with proper error handling.',
+    verification: 'Ran npm test — all tests pass.',
+    deviations: 'None.',
+    knownIssues: 'None.',
+    keyFiles: ['src/middleware/auth.ts'],
+    keyDecisions: [],
+    blockerDiscovered: false,
+    verificationEvidence: [
+      { command: 'npm test', exitCode: 0, verdict: '✅ pass', durationMs: 2500 },
+    ],
+  };
+}
+
+// ─── Post-mutation hook: event log ───────────────────────────────────────
+
+test('post-mutation-hook: event-log.jsonl exists after handleCompleteTask', async () => {
+  const base = tempDir();
+  const dbPath = path.join(base, 'test.db');
+  openDatabase(dbPath);
+  createProject(base);
+
+  try {
+    const result = await handleCompleteTask(makeCompleteTaskParams(), base);
+    assert.ok(!('error' in result), `handler should succeed, got: ${JSON.stringify(result)}`);
+
+    const logPath = path.join(base, '.gsd', 'event-log.jsonl');
+    assert.ok(fs.existsSync(logPath), 'event-log.jsonl should exist after handler completes');
+  } finally {
+    closeDatabase();
+    cleanupDir(base);
+  }
+});
+
+test('post-mutation-hook: event log contains complete-task event with correct params', async () => {
+  const base = tempDir();
+  const dbPath = path.join(base, 'test.db');
+  openDatabase(dbPath);
+  createProject(base);
+
+  try {
+    await handleCompleteTask(makeCompleteTaskParams(), base);
+
+    const logPath = path.join(base, '.gsd', 'event-log.jsonl');
+    const events = readEvents(logPath);
+    assert.ok(events.length > 0, 'event log should have at least one event');
+
+    const ev = events.find((e) => e.cmd === 'complete-task');
+    assert.ok(ev !== undefined, 'should have a complete-task event');
+    assert.strictEqual((ev!.params as { milestoneId?: string }).milestoneId, 'M001');
+    assert.strictEqual((ev!.params as { sliceId?: string }).sliceId, 'S01');
+    assert.strictEqual((ev!.params as { taskId?: string }).taskId, 'T01');
+    assert.strictEqual(ev!.actor, 'agent');
+  } finally {
+    closeDatabase();
+    cleanupDir(base);
+  }
+});
+
+// ─── Post-mutation hook: manifest ────────────────────────────────────────
+
+test('post-mutation-hook: state-manifest.json exists after handleCompleteTask', async () => {
+  const base = tempDir();
+  const dbPath = path.join(base, 'test.db');
+  openDatabase(dbPath);
+  createProject(base);
+
+  try {
+    const result = await handleCompleteTask(makeCompleteTaskParams(), base);
+    assert.ok(!('error' in result), `handler should succeed, got: ${JSON.stringify(result)}`);
+
+    const manifestPath = path.join(base, '.gsd', 'state-manifest.json');
+    assert.ok(fs.existsSync(manifestPath), 'state-manifest.json should exist after handler completes');
+  } finally {
+    closeDatabase();
+    cleanupDir(base);
+  }
+});
+
+test('post-mutation-hook: manifest has version 1 and includes completed task', async () => {
+  const base = tempDir();
+  const dbPath = path.join(base, 'test.db');
+  openDatabase(dbPath);
+  createProject(base);
+
+  try {
+    await handleCompleteTask(makeCompleteTaskParams(), base);
+
+    const manifest = readManifest(base);
+    assert.ok(manifest !== null, 'manifest should be readable');
+    assert.strictEqual(manifest!.version, 1);
+
+    const task = manifest!.tasks.find((t) => t.id === 'T01');
+    assert.ok(task !== undefined, 'T01 should appear in manifest');
+    assert.strictEqual(task!.status, 'complete');
+    assert.strictEqual(task!.milestone_id, 'M001');
+    assert.strictEqual(task!.slice_id, 'S01');
+  } finally {
+    closeDatabase();
+    cleanupDir(base);
+  }
+});
+
+// ─── Post-mutation hook: non-fatal on hook failure ───────────────────────
+
+test('post-mutation-hook: handler still returns success even if projections dir is missing', async () => {
+  // basePath with NO .gsd directory — projections will fail to find milestones
+  // but handler should still return a result (not throw)
+  const base = tempDir();
+  const dbPath = path.join(base, 'test.db');
+  openDatabase(dbPath);
+
+  // Create tasks dir but NO plan file (projections will soft-fail)
+  const tasksDir = path.join(base, '.gsd', 'milestones', 'M001', 'slices', 'S01', 'tasks');
+  fs.mkdirSync(tasksDir, { recursive: true });
+
+  try {
+    const result = await handleCompleteTask(makeCompleteTaskParams(), base);
+    // Handler should succeed (post-hook failures are non-fatal)
+    assert.ok(!('error' in result), `handler should not propagate hook errors, got: ${JSON.stringify(result)}`);
+  } finally {
+    closeDatabase();
+    cleanupDir(base);
+  }
+});
diff --git a/src/resources/extensions/gsd/tests/sync-lock.test.ts b/src/resources/extensions/gsd/tests/sync-lock.test.ts
new file mode 100644
index 000000000..038c6ccb6
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/sync-lock.test.ts
@@ -0,0 +1,122 @@
+// GSD Extension — sync-lock unit tests
+// Tests acquireSyncLock() and releaseSyncLock().
+
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import * as os from 'node:os';
+import { acquireSyncLock, releaseSyncLock } from '../sync-lock.ts';
+
+function tempDir(): string {
+  return fs.mkdtempSync(path.join(os.tmpdir(), 'gsd-sync-lock-'));
+}
+
+function cleanupDir(dirPath: string): void {
+  try { fs.rmSync(dirPath, { recursive: true, force: true }); } catch { /* best effort */ }
+}
+
+// ─── acquireSyncLock ─────────────────────────────────────────────────────
+
+test('sync-lock: acquireSyncLock returns { acquired: true } when no lock exists', () => {
+  const base = tempDir();
+  fs.mkdirSync(path.join(base, '.gsd'), { recursive: true });
+  try {
+    const result = acquireSyncLock(base);
+    assert.strictEqual(result.acquired, true);
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+test('sync-lock: acquireSyncLock creates lock file at .gsd/sync.lock', () => {
+  const base = tempDir();
+  fs.mkdirSync(path.join(base, '.gsd'), { recursive: true });
+  try {
+    acquireSyncLock(base);
+    const lockPath = path.join(base, '.gsd', 'sync.lock');
+    assert.ok(fs.existsSync(lockPath), 'sync.lock should exist after acquire');
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+test('sync-lock: lock file contains pid and acquired_at fields', () => {
+  const base = tempDir();
+  fs.mkdirSync(path.join(base, '.gsd'), { recursive: true });
+  try {
+    acquireSyncLock(base);
+    const lockPath = path.join(base, '.gsd', 'sync.lock');
+    const content = JSON.parse(fs.readFileSync(lockPath, 'utf-8'));
+    assert.strictEqual(typeof content.pid, 'number');
+    assert.strictEqual(typeof content.acquired_at, 'string');
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+// ─── releaseSyncLock ─────────────────────────────────────────────────────
+
+test('sync-lock: releaseSyncLock removes lock file', () => {
+  const base = tempDir();
+  fs.mkdirSync(path.join(base, '.gsd'), { recursive: true });
+  try {
+    acquireSyncLock(base);
+    const lockPath = path.join(base, '.gsd', 'sync.lock');
+    assert.ok(fs.existsSync(lockPath), 'lock file should exist before release');
+    releaseSyncLock(base);
+    assert.ok(!fs.existsSync(lockPath), 'lock file should not exist after release');
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+test('sync-lock: releaseSyncLock is a no-op when no lock file exists', () => {
+  const base = tempDir();
+  fs.mkdirSync(path.join(base, '.gsd'), { recursive: true });
+  try {
+    // Should not throw
+    releaseSyncLock(base);
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+// ─── acquire → release → re-acquire round-trip ───────────────────────────
+
+test('sync-lock: can re-acquire after release', () => {
+  const base = tempDir();
+  fs.mkdirSync(path.join(base, '.gsd'), { recursive: true });
+  try {
+    const r1 = acquireSyncLock(base);
+    assert.strictEqual(r1.acquired, true, 'first acquire should succeed');
+    releaseSyncLock(base);
+    const r2 = acquireSyncLock(base);
+    assert.strictEqual(r2.acquired, true, 're-acquire after release should succeed');
+    releaseSyncLock(base);
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+// ─── stale lock override ─────────────────────────────────────────────────
+
+test('sync-lock: overrides stale lock file (mtime backdated)', (t) => {
+  const base = tempDir();
+  fs.mkdirSync(path.join(base, '.gsd'), { recursive: true });
+  const lockPath = path.join(base, '.gsd', 'sync.lock');
+  try {
+    // Write a lock file with a very old mtime (simulating staleness)
+    fs.writeFileSync(lockPath, JSON.stringify({ pid: 99999, acquired_at: new Date(0).toISOString() }));
+    // Backdate mtime by 2 minutes
+    const staleTime = new Date(Date.now() - 120_000);
+    fs.utimesSync(lockPath, staleTime, staleTime);
+
+    // Should override stale lock and acquire
+    const result = acquireSyncLock(base, 500);
+    assert.strictEqual(result.acquired, true, 'should acquire over stale lock');
+    releaseSyncLock(base);
+  } finally {
+    cleanupDir(base);
+  }
+});
diff --git a/src/resources/extensions/gsd/tests/workflow-events.test.ts b/src/resources/extensions/gsd/tests/workflow-events.test.ts
new file mode 100644
index 000000000..ee3f7f9ec
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/workflow-events.test.ts
@@ -0,0 +1,205 @@
+// GSD Extension — workflow-events unit tests
+// Tests appendEvent, readEvents, findForkPoint, compactMilestoneEvents.
+
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import * as os from 'node:os';
+import {
+  appendEvent,
+  readEvents,
+  findForkPoint,
+  compactMilestoneEvents,
+  type WorkflowEvent,
+} from '../workflow-events.ts';
+
+function tempDir(): string {
+  return fs.mkdtempSync(path.join(os.tmpdir(), 'gsd-events-'));
+}
+
+function cleanupDir(dirPath: string): void {
+  try { fs.rmSync(dirPath, { recursive: true, force: true }); } catch { /* best effort */ }
+}
+
+function makeEvent(cmd: string, params: Record<string, unknown> = {}): Omit<WorkflowEvent, 'hash'> {
+  return { cmd, params, ts: new Date().toISOString(), actor: 'agent' };
+}
+
+// ─── appendEvent ─────────────────────────────────────────────────────────
+
+test('workflow-events: appendEvent creates .gsd dir and event-log.jsonl', () => {
+  const base = tempDir();
+  try {
+    appendEvent(base, makeEvent('complete-task', { milestoneId: 'M001', taskId: 'T01' }));
+    assert.ok(fs.existsSync(path.join(base, '.gsd', 'event-log.jsonl')));
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+test('workflow-events: appendEvent writes valid JSON line', () => {
+  const base = tempDir();
+  try {
+    appendEvent(base, makeEvent('complete-task', { milestoneId: 'M001', taskId: 'T01' }));
+    const content = fs.readFileSync(path.join(base, '.gsd', 'event-log.jsonl'), 'utf-8');
+    const lines = content.trim().split('\n');
+    assert.strictEqual(lines.length, 1);
+    const parsed = JSON.parse(lines[0]!) as WorkflowEvent;
+    assert.strictEqual(parsed.cmd, 'complete-task');
+    assert.strictEqual(parsed.actor, 'agent');
+    assert.strictEqual(typeof parsed.hash, 'string');
+    assert.strictEqual(parsed.hash.length, 16);
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+test('workflow-events: appendEvent appends multiple events', () => {
+  const base = tempDir();
+  try {
+    appendEvent(base, makeEvent('complete-task', { taskId: 'T01' }));
+    appendEvent(base, makeEvent('complete-slice', { sliceId: 'S01' }));
+    const events = readEvents(path.join(base, '.gsd', 'event-log.jsonl'));
+    assert.strictEqual(events.length, 2);
+    assert.strictEqual(events[0]!.cmd, 'complete-task');
+    assert.strictEqual(events[1]!.cmd, 'complete-slice');
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+test('workflow-events: same cmd+params → same hash (deterministic)', () => {
+  const base = tempDir();
+  try {
+    appendEvent(base, makeEvent('plan-task', { milestoneId: 'M001', sliceId: 'S01' }));
+    appendEvent(base, makeEvent('plan-task', { milestoneId: 'M001', sliceId: 'S01' }));
+    const events = readEvents(path.join(base, '.gsd', 'event-log.jsonl'));
+    assert.strictEqual(events[0]!.hash, events[1]!.hash, 'identical cmd+params produce identical hash');
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+test('workflow-events: different params → different hash', () => {
+  const base = tempDir();
+  try {
+    appendEvent(base, makeEvent('complete-task', { taskId: 'T01' }));
+    appendEvent(base, makeEvent('complete-task', { taskId: 'T02' }));
+    const events = readEvents(path.join(base, '.gsd', 'event-log.jsonl'));
+    assert.notStrictEqual(events[0]!.hash, events[1]!.hash, 'different params produce different hash');
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+// ─── readEvents ──────────────────────────────────────────────────────────
+
+test('workflow-events: readEvents returns [] for non-existent file', () => {
+  const result = readEvents('/nonexistent/path/event-log.jsonl');
+  assert.deepStrictEqual(result, []);
+});
+
+test('workflow-events: readEvents skips corrupted lines', () => {
+  const base = tempDir();
+  try {
+    fs.mkdirSync(path.join(base, '.gsd'), { recursive: true });
+    const logPath = path.join(base, '.gsd', 'event-log.jsonl');
+    // Write a valid line, a corrupted line, and another valid line
+    fs.writeFileSync(logPath,
+      '{"cmd":"complete-task","params":{},"ts":"2026-01-01T00:00:00Z","hash":"abcd1234abcd1234","actor":"agent"}\n' +
+      'NOT VALID JSON {{{{\n' +
+      '{"cmd":"plan-task","params":{},"ts":"2026-01-01T00:00:01Z","hash":"1234abcd1234abcd","actor":"system"}\n',
+    );
+    const events = readEvents(logPath);
+    assert.strictEqual(events.length, 2, 'should return 2 valid events, skipping the corrupted line');
+    assert.strictEqual(events[0]!.cmd, 'complete-task');
+    assert.strictEqual(events[1]!.cmd, 'plan-task');
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+// ─── findForkPoint ───────────────────────────────────────────────────────
+
+test('workflow-events: findForkPoint returns -1 for two empty logs', () => {
+  assert.strictEqual(findForkPoint([], []), -1);
+});
+
+test('workflow-events: findForkPoint returns -1 when first events differ', () => {
+  const e1 = { cmd: 'a', params: {}, ts: '', hash: 'hash1', actor: 'agent' } as WorkflowEvent;
+  const e2 = { cmd: 'b', params: {}, ts: '', hash: 'hash2', actor: 'agent' } as WorkflowEvent;
+  assert.strictEqual(findForkPoint([e1], [e2]), -1);
+});
+
+test('workflow-events: findForkPoint returns 0 when only first event is common', () => {
+  const common = { cmd: 'a', params: {}, ts: '', hash: 'hash1', actor: 'agent' } as WorkflowEvent;
+  const eA = { cmd: 'b', params: {}, ts: '', hash: 'hash2', actor: 'agent' } as WorkflowEvent;
+  const eB = { cmd: 'c', params: {}, ts: '', hash: 'hash3', actor: 'agent' } as WorkflowEvent;
+  // logA: [common, eA], logB: [common, eB]
+  assert.strictEqual(findForkPoint([common, eA], [common, eB]), 0);
+});
+
+test('workflow-events: findForkPoint returns last common index for prefix relationship', () => {
+  const e1 = { cmd: 'a', params: {}, ts: '', hash: 'h1', actor: 'agent' } as WorkflowEvent;
+  const e2 = { cmd: 'b', params: {}, ts: '', hash: 'h2', actor: 'agent' } as WorkflowEvent;
+  const e3 = { cmd: 'c', params: {}, ts: '', hash: 'h3', actor: 'agent' } as WorkflowEvent;
+  // logA is a prefix of logB → fork point is last index of logA
+  assert.strictEqual(findForkPoint([e1, e2], [e1, e2, e3]), 1);
+});
+
+test('workflow-events: findForkPoint handles equal logs', () => {
+  const e1 = { cmd: 'a', params: {}, ts: '', hash: 'h1', actor: 'agent' } as WorkflowEvent;
+  const e2 = { cmd: 'b', params: {}, ts: '', hash: 'h2', actor: 'agent' } as WorkflowEvent;
+  assert.strictEqual(findForkPoint([e1, e2], [e1, e2]), 1);
+});
+
+// ─── compactMilestoneEvents ──────────────────────────────────────────────
+
+test('workflow-events: compactMilestoneEvents returns { archived: 0 } when no matching events', () => {
+  const base = tempDir();
+  try {
+    appendEvent(base, makeEvent('complete-task', { milestoneId: 'M002', taskId: 'T01' }));
+    const result = compactMilestoneEvents(base, 'M001');
+    assert.strictEqual(result.archived, 0);
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+test('workflow-events: compactMilestoneEvents archives milestone events', () => {
+  const base = tempDir();
+  try {
+    appendEvent(base, makeEvent('complete-task', { milestoneId: 'M001', taskId: 'T01' }));
+    appendEvent(base, makeEvent('complete-task', { milestoneId: 'M001', taskId: 'T02' }));
+    appendEvent(base, makeEvent('complete-task', { milestoneId: 'M002', taskId: 'T03' }));
+
+    const result = compactMilestoneEvents(base, 'M001');
+    assert.strictEqual(result.archived, 2, 'should archive 2 M001 events');
+
+    // Archive file should exist
+    const archivePath = path.join(base, '.gsd', 'event-log-M001.jsonl.archived');
+    assert.ok(fs.existsSync(archivePath), 'archive file should exist');
+    const archived = readEvents(archivePath);
+    assert.strictEqual(archived.length, 2, 'archive file should have 2 events');
+
+    // Active log should retain only M002 event
+    const active = readEvents(path.join(base, '.gsd', 'event-log.jsonl'));
+    assert.strictEqual(active.length, 1, 'active log should have 1 remaining event');
+    assert.strictEqual((active[0]!.params as { milestoneId?: string }).milestoneId, 'M002');
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+test('workflow-events: compactMilestoneEvents empties active log when all events are from milestone', () => {
+  const base = tempDir();
+  try {
+    appendEvent(base, makeEvent('complete-task', { milestoneId: 'M001', taskId: 'T01' }));
+    compactMilestoneEvents(base, 'M001');
+    const active = readEvents(path.join(base, '.gsd', 'event-log.jsonl'));
+    assert.strictEqual(active.length, 0, 'active log should be empty after full compact');
+  } finally {
+    cleanupDir(base);
+  }
+});
diff --git a/src/resources/extensions/gsd/tests/workflow-manifest.test.ts b/src/resources/extensions/gsd/tests/workflow-manifest.test.ts
new file mode 100644
index 000000000..fa0618cbb
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/workflow-manifest.test.ts
@@ -0,0 +1,186 @@
+// GSD Extension — workflow-manifest unit tests
+// Tests writeManifest, readManifest, snapshotState, bootstrapFromManifest.
+
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import * as os from 'node:os';
+import {
+  openDatabase,
+  closeDatabase,
+  insertMilestone,
+  insertSlice,
+  insertTask,
+} from '../gsd-db.ts';
+import {
+  writeManifest,
+  readManifest,
+  snapshotState,
+  bootstrapFromManifest,
+} from '../workflow-manifest.ts';
+
+function tempDir(): string {
+  return fs.mkdtempSync(path.join(os.tmpdir(), 'gsd-manifest-'));
+}
+
+function tempDbPath(base: string): string {
+  return path.join(base, 'test.db');
+}
+
+function cleanupDir(dirPath: string): void {
+  try { fs.rmSync(dirPath, { recursive: true, force: true }); } catch { /* best effort */ }
+}
+
+// ─── readManifest: no file ────────────────────────────────────────────────
+
+test('workflow-manifest: readManifest returns null when file does not exist', () => {
+  const base = tempDir();
+  try {
+    const result = readManifest(base);
+    assert.strictEqual(result, null);
+  } finally {
+    cleanupDir(base);
+  }
+});
+
+// ─── writeManifest + readManifest round-trip ─────────────────────────────
+
+test('workflow-manifest: writeManifest creates state-manifest.json with version 1', () => {
+  const base = tempDir();
+  openDatabase(tempDbPath(base));
+  try {
+    writeManifest(base);
+    const manifestPath = path.join(base, '.gsd', 'state-manifest.json');
+    assert.ok(fs.existsSync(manifestPath), 'state-manifest.json should exist');
+    const raw = JSON.parse(fs.readFileSync(manifestPath, 'utf-8'));
+    assert.strictEqual(raw.version, 1);
+  } finally {
+    closeDatabase();
+    cleanupDir(base);
+  }
+});
+
+test('workflow-manifest: readManifest parses manifest written by writeManifest', () => {
+  const base = tempDir();
+  openDatabase(tempDbPath(base));
+  try {
+    writeManifest(base);
+    const manifest = readManifest(base);
+    assert.ok(manifest !== null);
+    assert.strictEqual(manifest!.version, 1);
+    assert.ok(typeof manifest!.exported_at === 'string');
+    assert.ok(Array.isArray(manifest!.milestones));
+    assert.ok(Array.isArray(manifest!.slices));
+    assert.ok(Array.isArray(manifest!.tasks));
+    assert.ok(Array.isArray(manifest!.decisions));
+    assert.ok(Array.isArray(manifest!.verification_evidence));
+  } finally {
+    closeDatabase();
+    cleanupDir(base);
+  }
+});
+
+// ─── snapshotState: captures DB rows ─────────────────────────────────────
+
+test('workflow-manifest: snapshotState includes inserted milestone', () => {
+  const base = tempDir();
+  openDatabase(tempDbPath(base));
+  try {
+    insertMilestone({ id: 'M001', title: 'Auth Milestone' });
+    const snap = snapshotState();
+    assert.strictEqual(snap.version, 1);
+    const m = snap.milestones.find((r) => r.id === 'M001');
+    assert.ok(m !== undefined, 'M001 should appear in snapshot');
+    assert.strictEqual(m!.title, 'Auth Milestone');
+  } finally {
+    closeDatabase();
+    cleanupDir(base);
+  }
+});
+
+test('workflow-manifest: snapshotState captures tasks', () => {
+  const base = tempDir();
+  openDatabase(tempDbPath(base));
+  try {
+    insertMilestone({ id: 'M001' });
+    insertSlice({ id: 'S01', milestoneId: 'M001' });
+    insertTask({ id: 'T01', sliceId: 'S01', milestoneId: 'M001', title: 'Do thing', status: 'complete' });
+    const snap = snapshotState();
+    const t = snap.tasks.find((r) => r.id === 'T01');
+    assert.ok(t !== undefined, 'T01 should appear in snapshot');
+    assert.strictEqual(t!.status, 'complete');
+  } finally {
+    closeDatabase();
+    cleanupDir(base);
+  }
+});
+
+// ─── bootstrapFromManifest ────────────────────────────────────────────────
+
+test('workflow-manifest: bootstrapFromManifest returns false when no manifest file', () => {
+  const base = tempDir();
+  openDatabase(tempDbPath(base));
+  try {
+    const result = bootstrapFromManifest(base);
+    assert.strictEqual(result, false);
+  } finally {
+    closeDatabase();
+    cleanupDir(base);
+  }
+});
+
+test('workflow-manifest: bootstrapFromManifest restores DB from manifest (round-trip)', () => {
+  const base = tempDir();
+  openDatabase(tempDbPath(base));
+  try {
+    // Insert data and write manifest
+    insertMilestone({ id: 'M001', title: 'Restored Milestone' });
+    insertSlice({ id: 'S01', milestoneId: 'M001', title: 'Restored Slice' });
+    insertTask({ id: 'T01', sliceId: 'S01', milestoneId: 'M001', title: 'Restored Task', status: 'complete' });
+    writeManifest(base);
+    closeDatabase();
+
+    // Open a fresh DB and bootstrap from manifest
+    const newDbPath = path.join(base, 'new.db');
+    openDatabase(newDbPath);
+    const result = bootstrapFromManifest(base);
+    assert.strictEqual(result, true, 'bootstrapFromManifest should return true');
+
+    // Verify restored state
+    const snap = snapshotState();
+    const m = snap.milestones.find((r) => r.id === 'M001');
+    assert.ok(m !== undefined, 'M001 should be restored');
+    assert.strictEqual(m!.title, 'Restored Milestone');
+
+    const s = snap.slices.find((r) => r.id === 'S01');
+    assert.ok(s !== undefined, 'S01 should be restored');
+
+    const t = snap.tasks.find((r) => r.id === 'T01');
+    assert.ok(t !== undefined, 'T01 should be restored');
+    assert.strictEqual(t!.status, 'complete');
+  } finally {
+    closeDatabase();
+    cleanupDir(base);
+  }
+});
+
+// ─── readManifest: version check ─────────────────────────────────────────
+
+test('workflow-manifest: readManifest throws on unsupported version', () => {
+  const base = tempDir();
+  try {
+    fs.mkdirSync(path.join(base, '.gsd'), { recursive: true });
+    fs.writeFileSync(
+      path.join(base, '.gsd', 'state-manifest.json'),
+      JSON.stringify({ version: 99, exported_at: '', milestones: [], slices: [], tasks: [], decisions: [], verification_evidence: [] }),
+    );
+    assert.throws(
+      () => readManifest(base),
+      /Unsupported manifest version/,
+      'should throw on version mismatch',
+    );
+  } finally {
+    cleanupDir(base);
+  }
+});
diff --git a/src/resources/extensions/gsd/tests/workflow-projections.test.ts b/src/resources/extensions/gsd/tests/workflow-projections.test.ts
new file mode 100644
index 000000000..9d26da900
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/workflow-projections.test.ts
@@ -0,0 +1,170 @@
+// GSD Extension — workflow-projections unit tests
+// Tests the pure rendering functions (no DB required).
+
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { renderPlanContent } from '../workflow-projections.ts';
+import type { SliceRow, TaskRow } from '../gsd-db.ts';
+
+// ─── Test fixtures ────────────────────────────────────────────────────────
+
+function makeSlice(overrides: Partial<SliceRow> = {}): SliceRow {
+  return {
+    id: 'S01',
+    milestone_id: 'M001',
+    title: 'Auth Layer',
+    status: 'active',
+    risk: 'high',
+    depends: [],
+    demo: 'Login flow works end-to-end',
+    goal: 'Implement JWT authentication',
+    full_summary_md: '',
+    full_uat_md: '',
+    success_criteria: '',
+    proof_level: '',
+    integration_closure: '',
+    observability_impact: '',
+    created_at: '2026-01-01T00:00:00Z',
+    completed_at: null,
+    sequence: 1,
+    replan_triggered_at: null,
+    ...overrides,
+  };
+}
+
+function makeTask(overrides: Partial<TaskRow> = {}): TaskRow {
+  return {
+    id: 'T01',
+    slice_id: 'S01',
+    milestone_id: 'M001',
+    title: 'Create JWT middleware',
+    status: 'pending',
+    description: 'Implement JWT validation middleware',
+    estimate: '2h',
+    files: ['src/middleware/auth.ts'],
+    verify: 'npm test src/middleware/auth.test.ts',
+    one_liner: '',
+    narrative: '',
+    verification_result: '',
+    duration: '',
+    completed_at: null,
+    blocker_discovered: false,
+    deviations: '',
+    known_issues: '',
+    key_files: [],
+    key_decisions: [],
+    full_summary_md: '',
+    inputs: [],
+    expected_output: [],
+    observability_impact: '',
+    sequence: 1,
+    ...overrides,
+  };
+}
+
+// ─── renderPlanContent: structure ────────────────────────────────────────
+
+test('workflow-projections: renderPlanContent starts with H1 containing slice id and title', () => {
+  const content = renderPlanContent(makeSlice(), []);
+  assert.ok(content.startsWith('# S01: Auth Layer'), `expected H1, got: ${content.slice(0, 60)}`);
+});
+
+test('workflow-projections: renderPlanContent includes Goal line', () => {
+  const content = renderPlanContent(makeSlice(), []);
+  assert.ok(content.includes('**Goal:** Implement JWT authentication'));
+});
+
+test('workflow-projections: renderPlanContent includes Demo line', () => {
+  const content = renderPlanContent(makeSlice(), []);
+  assert.ok(content.includes('**Demo:** After this: Login flow works end-to-end'));
+});
+
+test('workflow-projections: renderPlanContent falls back to TBD when goal and full_summary_md are empty', () => {
+  const slice = makeSlice({ goal: '', full_summary_md: '' });
+  const content = renderPlanContent(slice, []);
+  assert.ok(content.includes('**Goal:** TBD'));
+});
+
+test('workflow-projections: renderPlanContent falls back to full_summary_md when goal is empty', () => {
+  const slice = makeSlice({ goal: '', full_summary_md: 'Fallback goal text' });
+  const content = renderPlanContent(slice, []);
+  assert.ok(content.includes('**Goal:** Fallback goal text'));
+});
+
+test('workflow-projections: renderPlanContent includes ## Tasks section', () => {
+  const content = renderPlanContent(makeSlice(), []);
+  assert.ok(content.includes('## Tasks'));
+});
+
+// ─── renderPlanContent: task checkboxes ──────────────────────────────────
+
+test('workflow-projections: pending task renders with [ ] checkbox', () => {
+  const task = makeTask({ status: 'pending' });
+  const content = renderPlanContent(makeSlice(), [task]);
+  assert.ok(content.includes('- [ ] **T01:**'), `expected unchecked, got: ${content}`);
+});
+
+test('workflow-projections: done task renders with [x] checkbox', () => {
+  const task = makeTask({ status: 'done' });
+  const content = renderPlanContent(makeSlice(), [task]);
+  assert.ok(content.includes('- [x] **T01:**'), `expected checked, got: ${content}`);
+});
+
+test('workflow-projections: non-done status renders with [ ] checkbox', () => {
+  const task = makeTask({ status: 'complete' }); // 'complete' ≠ 'done' → unchecked
+  const content = renderPlanContent(makeSlice(), [task]);
+  assert.ok(content.includes('- [ ] **T01:**'));
+});
+
+// ─── renderPlanContent: task sublines ────────────────────────────────────
+
+test('workflow-projections: task with estimate renders Estimate subline', () => {
+  const task = makeTask({ estimate: '2h' });
+  const content = renderPlanContent(makeSlice(), [task]);
+  assert.ok(content.includes('  - Estimate: 2h'));
+});
+
+test('workflow-projections: task with empty estimate omits Estimate subline', () => {
+  const task = makeTask({ estimate: '' });
+  const content = renderPlanContent(makeSlice(), [task]);
+  assert.ok(!content.includes('  - Estimate:'));
+});
+
+test('workflow-projections: task with files renders Files subline', () => {
+  const task = makeTask({ files: ['src/auth.ts', 'src/auth.test.ts'] });
+  const content = renderPlanContent(makeSlice(), [task]);
+  assert.ok(content.includes('  - Files: src/auth.ts, src/auth.test.ts'));
+});
+
+test('workflow-projections: task with empty files array omits Files subline', () => {
+  const task = makeTask({ files: [] });
+  const content = renderPlanContent(makeSlice(), [task]);
+  assert.ok(!content.includes('  - Files:'));
+});
+
+test('workflow-projections: task with verify renders Verify subline', () => {
+  const task = makeTask({ verify: 'npm test' });
+  const content = renderPlanContent(makeSlice(), [task]);
+  assert.ok(content.includes('  - Verify: npm test'));
+});
+
+test('workflow-projections: task with no verify omits Verify subline', () => {
+  const task = makeTask({ verify: '' });
+  const content = renderPlanContent(makeSlice(), [task]);
+  assert.ok(!content.includes('  - Verify:'));
+});
+
+test('workflow-projections: task with duration renders Duration subline', () => {
+  const task = makeTask({ duration: '45m' });
+  const content = renderPlanContent(makeSlice(), [task]);
+  assert.ok(content.includes('  - Duration: 45m'));
+});
+
+test('workflow-projections: multiple tasks rendered in order', () => {
+  const t1 = makeTask({ id: 'T01', title: 'First task', sequence: 1 });
+  const t2 = makeTask({ id: 'T02', title: 'Second task', sequence: 2 });
+  const content = renderPlanContent(makeSlice(), [t1, t2]);
+  const idxT1 = content.indexOf('**T01:**');
+  const idxT2 = content.indexOf('**T02:**');
+  assert.ok(idxT1 < idxT2, 'T01 should appear before T02');
+});
diff --git a/src/resources/extensions/gsd/tests/write-intercept.test.ts b/src/resources/extensions/gsd/tests/write-intercept.test.ts
new file mode 100644
index 000000000..940295376
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/write-intercept.test.ts
@@ -0,0 +1,77 @@
+// GSD Extension — write-intercept unit tests
+// Tests isBlockedStateFile() and BLOCKED_WRITE_ERROR constant.
+
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { isBlockedStateFile, BLOCKED_WRITE_ERROR } from '../write-intercept.ts';
+
+// ─── isBlockedStateFile: blocked paths ───────────────────────────────────
+
+test('write-intercept: blocks unix .gsd/STATE.md path', () => {
+  assert.strictEqual(isBlockedStateFile('/project/.gsd/STATE.md'), true);
+});
+
+test('write-intercept: blocks relative path with dir prefix before .gsd/STATE.md', () => {
+  // The regex requires a path separator before .gsd — bare '.gsd/STATE.md' is not blocked
+  // but 'project/.gsd/STATE.md' is (has separator before .gsd)
+  assert.strictEqual(isBlockedStateFile('project/.gsd/STATE.md'), true);
+});
+
+test('write-intercept: does NOT block bare .gsd/STATE.md without leading separator', () => {
+  // Regex requires [/\\] before .gsd — bare relative path has no such separator
+  assert.strictEqual(isBlockedStateFile('.gsd/STATE.md'), false);
+});
+
+test('write-intercept: blocks nested project .gsd/STATE.md path', () => {
+  assert.strictEqual(isBlockedStateFile('/Users/dev/my-project/.gsd/STATE.md'), true);
+});
+
+test('write-intercept: blocks .gsd/projects/<name>/STATE.md (symlinked projects path)', () => {
+  assert.strictEqual(isBlockedStateFile('/home/user/.gsd/projects/my-project/STATE.md'), true);
+});
+
+// ─── isBlockedStateFile: allowed paths ───────────────────────────────────
+
+test('write-intercept: allows .gsd/ROADMAP.md', () => {
+  assert.strictEqual(isBlockedStateFile('/project/.gsd/ROADMAP.md'), false);
+});
+
+test('write-intercept: allows .gsd/PLAN.md', () => {
+  assert.strictEqual(isBlockedStateFile('/project/.gsd/PLAN.md'), false);
+});
+
+test('write-intercept: allows .gsd/REQUIREMENTS.md', () => {
+  assert.strictEqual(isBlockedStateFile('/project/.gsd/REQUIREMENTS.md'), false);
+});
+
+test('write-intercept: allows .gsd/SUMMARY.md', () => {
+  assert.strictEqual(isBlockedStateFile('/project/.gsd/SUMMARY.md'), false);
+});
+
+test('write-intercept: allows .gsd/PROJECT.md', () => {
+  assert.strictEqual(isBlockedStateFile('/project/.gsd/PROJECT.md'), false);
+});
+
+test('write-intercept: allows regular source files', () => {
+  assert.strictEqual(isBlockedStateFile('/project/src/index.ts'), false);
+});
+
+test('write-intercept: allows slice plan files', () => {
+  assert.strictEqual(isBlockedStateFile('/project/.gsd/milestones/M001/slices/S01/S01-PLAN.md'), false);
+});
+
+test('write-intercept: does not block files named STATE.md outside .gsd/', () => {
+  assert.strictEqual(isBlockedStateFile('/project/docs/STATE.md'), false);
+});
+
+// ─── BLOCKED_WRITE_ERROR: content ────────────────────────────────────────
+
+test('write-intercept: BLOCKED_WRITE_ERROR is a non-empty string', () => {
+  assert.strictEqual(typeof BLOCKED_WRITE_ERROR, 'string');
+  assert.ok(BLOCKED_WRITE_ERROR.length > 0);
+});
+
+test('write-intercept: BLOCKED_WRITE_ERROR mentions engine tool calls', () => {
+  assert.ok(BLOCKED_WRITE_ERROR.includes('gsd_complete_task'), 'should mention gsd_complete_task');
+  assert.ok(BLOCKED_WRITE_ERROR.includes('engine tool calls'), 'should mention engine tool calls');
+});