diff --git a/e2e/integrity.test.ts b/e2e/integrity.test.ts
new file mode 100644
index 0000000..fe3676c
--- /dev/null
+++ b/e2e/integrity.test.ts
@@ -0,0 +1,275 @@
+import { execFileSync, spawn } from 'node:child_process';
+import { existsSync, readFileSync } from 'node:fs';
+import { join } from 'node:path';
+import { expect, test } from '@playwright/test';
+import {
+  assertCliBuilt,
+  CLI_BIN,
+  createCliMachine,
+  type CliMachine,
+  type ExecResult,
+  freePort,
+  TARGET_FQDN,
+} from './helpers.js';
+
+// Data-integrity tier: proves the store guarantees the docs claim but no other tier verifies -
+// the daemon's single-writer serialization under concurrency, path-traversal rejection, no-op
+// write idempotence, stdin round-trip, graceful offline degradation, and non-destructive vault
+// removal. All offline: daemon tests speak loopback + local git, the rest use the in-process
+// engine with egress blackholed. @p0
+const BLACKHOLE = 'http://127.0.0.1:1';
+const OFFLINE = {
+  http_proxy: BLACKHOLE,
+  https_proxy: BLACKHOLE,
+  HTTP_PROXY: BLACKHOLE,
+  HTTPS_PROXY: BLACKHOLE,
+};
+
+const git = (dir: string, args: string[]): string =>
+  execFileSync('git', ['-C', dir, ...args], { encoding: 'utf-8' });
+
+const commitCount = (dir: string): number =>
+  Number.parseInt(git(dir, ['rev-list', '--count', 'HEAD']).trim(), 10);
+
+const workingTreeClean = (dir: string): boolean =>
+  git(dir, ['status', '--porcelain']).trim() === '';
+
+const hasIndexLock = (dir: string): boolean => existsSync(join(dir, '.git', 'index.lock'));
+
+// A corrupt object DB fails fsck with a non-zero exit; a clean repo returns 0.
+const fsckClean = (dir: string): boolean => {
+  try {
+    execFileSync('git', ['-C', dir, 'fsck', '--full'], { encoding: 'utf-8', stdio: 'pipe' });
+    return true;
+  } catch {
+    return false;
+  }
+};
+
+const daemonPid = (m: CliMachine): number | null => {
+  const p = join(m.configDir, 'daemon.pid');
+  return existsSync(p) ? Number.parseInt(readFileSync(p, 'utf-8').trim(), 10) : null;
+};
+
+const alive = (pid: number): boolean => {
+  try {
+    process.kill(pid, 0);
+    return true;
+  } catch {
+    return false;
+  }
+};
+
+// Pipe a body to the CLI over stdin (helpers.exec can't). Mirrors createCliMachine's env.
+const execStdin = (configDir: string, args: string[], stdin: string): Promise<ExecResult> =>
+  new Promise((resolve) => {
+    const child = spawn(process.execPath, [CLI_BIN, ...args], {
+      env: {
+        ...process.env,
+        AGENTAGE_CONFIG_DIR: configDir,
+        AGENTAGE_SITE_FQDN: TARGET_FQDN,
+        NO_COLOR: '1',
+        AGENTAGE_NO_DAEMON: '1',
+      },
+    });
+    let out = '';
+    child.stdout.on('data', (c: Buffer) => (out += c.toString()));
+    child.stderr.on('data', (c: Buffer) => (out += c.toString()));
+    child.on('close', (code) => resolve({ stdout: out, stderr: out, code: code ?? 1 }));
+    child.stdin.write(stdin);
+    child.stdin.end();
+  });
+
+test.describe('store data integrity @p0', () => {
+  test.beforeAll(() => assertCliBuilt());
+
+  test('10 concurrent writes serialize into 10 clean commits', async () => {
+    const port = await freePort();
+    const m = createCliMachine({ AGENTAGE_NO_DAEMON: '', AGENTAGE_DAEMON_PORT: String(port) });
+    const vaultDir = join(m.configDir, 'main');
+    let pid: number | null = null;
+    try {
+      expect((await m.exec(['vault', 'add', 'main', '--local', vaultDir])).code).toBe(0);
+      expect((await m.exec(['daemon', 'start'])).code).toBe(0);
+      pid = daemonPid(m);
+
+      // Ten writes to distinct paths, fired at once; the daemon's single engine serializes them.
+      const writes = await Promise.all(
+        Array.from({ length: 10 }, (_, i) =>
+          m.exec(['memory', 'write', `notes/n${i}.md`, '--body', `body-${i}`])
+        )
+      );
+      for (const w of writes) expect(w.code, w.stderr).toBe(0);
+
+      const reads = await Promise.all(
+        Array.from({ length: 10 }, (_, i) => m.exec(['memory', 'read', `notes/n${i}.md`]))
+      );
+      reads.forEach((r, i) => {
+        expect(r.code, r.stderr).toBe(0);
+        expect(r.stdout).toContain(`body-${i}`);
+      });
+
+      expect(commitCount(vaultDir)).toBe(10);
+      expect(workingTreeClean(vaultDir)).toBe(true);
+      expect(hasIndexLock(vaultDir)).toBe(false);
+      expect(fsckClean(vaultDir)).toBe(true);
+    } finally {
+      await m.exec(['daemon', 'stop']).catch(() => undefined);
+      if (pid !== null && alive(pid)) process.kill(pid, 'SIGKILL');
+      m.cleanup();
+    }
+  });
+
+  test('5 concurrent writes to one path keep the repo consistent', async () => {
+    const port = await freePort();
+    const m = createCliMachine({ AGENTAGE_NO_DAEMON: '', AGENTAGE_DAEMON_PORT: String(port) });
+    const vaultDir = join(m.configDir, 'main');
+    const bodies = Array.from({ length: 5 }, (_, i) => `body-${i}`);
+    let pid: number | null = null;
+    try {
+      expect((await m.exec(['vault', 'add', 'main', '--local', vaultDir])).code).toBe(0);
+      expect((await m.exec(['daemon', 'start'])).code).toBe(0);
+      pid = daemonPid(m);
+
+      const writes = await Promise.all(
+        bodies.map((b) => m.exec(['memory', 'write', 'notes/same.md', '--body', b]))
+      );
+      for (const w of writes) expect(w.code, w.stderr).toBe(0);
+
+      // Last-writer-wins: the surviving content is exactly one of the five, never a torn blend.
+      const read = await m.exec(['memory', 'read', 'notes/same.md']);
+      expect(read.code, read.stderr).toBe(0);
+      expect(bodies).toContain(read.stdout.trim());
+
+      // Five distinct bodies applied serially -> five commits, no torn index.
+      expect(commitCount(vaultDir)).toBe(5);
+      expect(workingTreeClean(vaultDir)).toBe(true);
+      expect(hasIndexLock(vaultDir)).toBe(false);
+      expect(fsckClean(vaultDir)).toBe(true);
+    } finally {
+      await m.exec(['daemon', 'stop']).catch(() => undefined);
+      if (pid !== null && alive(pid)) process.kill(pid, 'SIGKILL');
+      m.cleanup();
+    }
+  });
+
+  test('path traversal and absolute paths are refused, nothing escapes the vault', async () => {
+    const m = createCliMachine(OFFLINE);
+    try {
+      const vaultDir = join(m.configDir, 'main');
+      expect((await m.exec(['vault', 'add', 'main', '--local', vaultDir])).code).toBe(0);
+
+      const escape = join(m.configDir, 'escape.md'); // one level above the vault root
+      const abs = join(m.configDir, 'abs-escape.md');
+      const attempts: Array<[string, string]> = [
+        ['../escape.md', escape],
+        ['@main/../escape.md', escape],
+        [abs, abs], // an absolute path
+      ];
+      for (const [ref, leaked] of attempts) {
+        const res = await m.exec(['memory', 'write', ref, '--body', 'x']);
+        expect(res.code, `write ${ref} should be refused`).not.toBe(0);
+        expect(res.stderr + res.stdout).toContain('invalid path');
+        expect(existsSync(leaked), `${leaked} must not be created`).toBe(false);
+      }
+    } finally {
+      m.cleanup();
+    }
+  });
+
+  test('a no-op write adds no commit and reports the current HEAD', async () => {
+    const m = createCliMachine(OFFLINE);
+    try {
+      const vaultDir = join(m.configDir, 'main');
+      expect((await m.exec(['vault', 'add', 'main', '--local', vaultDir])).code).toBe(0);
+
+      const first = await m.exec([
+        'memory',
+        'write',
+        'notes/x.md',
+        '--body',
+        'identical',
+        '--json',
+      ]);
+      expect(first.code, first.stderr).toBe(0);
+      const rev1 = (JSON.parse(first.stdout) as { rev: string }).rev;
+      const commitsBefore = commitCount(vaultDir);
+
+      const second = await m.exec([
+        'memory',
+        'write',
+        'notes/x.md',
+        '--body',
+        'identical',
+        '--json',
+      ]);
+      expect(second.code, second.stderr).toBe(0);
+      const rev2 = (JSON.parse(second.stdout) as { rev: string }).rev;
+
+      expect(rev2).toBe(rev1); // no new commit was minted
+      expect(commitCount(vaultDir)).toBe(commitsBefore);
+      expect(rev2).toBe(git(vaultDir, ['rev-parse', 'HEAD']).trim());
+    } finally {
+      m.cleanup();
+    }
+  });
+
+  test('a body piped over stdin round-trips', async () => {
+    const m = createCliMachine();
+    try {
+      const vaultDir = join(m.configDir, 'main');
+      expect((await m.exec(['vault', 'add', 'main', '--local', vaultDir])).code).toBe(0);
+
+      const body = 'piped-body-marsupial';
+      const write = await execStdin(
+        m.configDir,
+        ['memory', 'write', 'notes/x.md', '--body', '-'],
+        body
+      );
+      expect(write.code, write.stdout).toBe(0);
+
+      const read = await m.exec(['memory', 'read', 'notes/x.md']);
+      expect(read.stdout).toContain(body);
+    } finally {
+      m.cleanup();
+    }
+  });
+
+  test('the offline update check degrades to a calm verdict, exit 0, no traceback', async () => {
+    // Point the endpoint at a reserved, unresolvable host so the check must fail its lookup.
+    const m = createCliMachine({ ...OFFLINE, AGENTAGE_SITE_FQDN: 'offline.invalid' });
+    try {
+      const res = await m.exec(['update', '--check'], 20_000);
+      expect(res.code, res.stderr).toBe(0); // exit 0 means it neither hung (killed) nor threw
+      expect(res.stdout.trim().length).toBeGreaterThan(0); // a verdict was printed
+      expect(/\bat\s+\S+\s+\(/.test(res.stderr + res.stdout), 'no stack trace').toBe(false);
+    } finally {
+      m.cleanup();
+    }
+  });
+
+  test('vault remove leaves the files and git history on disk', async () => {
+    const m = createCliMachine(OFFLINE);
+    try {
+      const vaultDir = join(m.configDir, 'main');
+      expect((await m.exec(['vault', 'add', 'main', '--local', vaultDir])).code).toBe(0);
+      expect((await m.exec(['memory', 'write', 'notes/keep.md', '--body', 'durable'])).code).toBe(
+        0
+      );
+      const commits = commitCount(vaultDir);
+
+      const rm = await m.exec(['vault', 'remove', 'main']);
+      expect(rm.code, rm.stderr).toBe(0);
+
+      // The registry entry is gone, but the on-disk repo is untouched.
+      expect(Object.keys(JSON.parse((await m.exec(['vault', 'list', '--json'])).stdout))).toEqual(
+        []
+      );
+      expect(existsSync(join(vaultDir, 'notes', 'keep.md'))).toBe(true);
+      expect(existsSync(join(vaultDir, '.git'))).toBe(true);
+      expect(commitCount(vaultDir)).toBe(commits);
+    } finally {
+      m.cleanup();
+    }
+  });
+});