feat(fpagent): pick the installer bundle for the host architecture

The hosted installer only ever chose the x86_64 bundle, so a 32-bit field
laptop running the public one-liner failed with "no compatible bundle" even
though fingerprint-agent v1.5.0 publishes fpagent-<version>-linux-i386.tar.gz.

Resolve the host architecture from uname -m (x86_64 or i386, else fail before
any download), then prefer -ubuntu-<codename>-<arch>.tar.gz and fall back to
-linux-<arch>.tar.gz. The version regex now derives the git hash for every
supported architecture, so a 32-bit install records and reports it too.

The help text matches the bundle installer: the systemd service and the
self-update timer are on by default, with --no-service, --no-updates and
--update-base documented.

tools/test/fpagent-install.test.js

@@ -37,6 +37,17 @@ const RELEASE = {
   ],
 };
 
+// A directory holding a fake `uname` that reports the given machine, so the
+// installer's architecture-sensitive picker runs on any CI host. PATH is
+// prepended with it; everything else resolves as usual.
+function fakeUname(machine) {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'fpagent-uname-'));
+  fs.writeFileSync(path.join(dir, 'uname'), `#!/bin/sh\nprintf '%s\\n' '${machine}'\n`, {
+    mode: 0o755,
+  });
+  return dir;
+}
+
 // Fake Gitea: refuses without the token, serves the release and its assets.
 async function startFakeGitea({ releaseStatus = 200, downloadStatus = 200 } = {}) {
   const calls = [];
@@ -231,6 +242,98 @@ test('install.sh is served publicly at /fpagent/install.sh', async () => {
   }
 });
 
+test('install.sh picks the bundle for the host architecture', async () => {
+  const calls = [];
+  const gateway = await startServer((req, res) => {
+    calls.push(req.url);
+    if (req.url === '/releases/latest') {
+      res.writeHead(200, { 'content-type': 'application/json' });
+      res.end(
+        JSON.stringify({
+          tag: 'v9.9.9',
+          assets: [
+            { name: 'fpagent-deadbee-linux-x86_64.tar.gz' },
+            { name: 'fpagent-deadbee-linux-x86_64.tar.gz.sha256' },
+            { name: 'fpagent-cafebabe-linux-i386.tar.gz' },
+            { name: 'fpagent-cafebabe-linux-i386.tar.gz.sha256' },
+          ],
+        })
+      );
+      return;
+    }
+    res.writeHead(404);
+    res.end();
+  });
+  const unameDir = fakeUname('i686');
+  const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'fpagent-arch-test-'));
+  try {
+    let out = '';
+    try {
+      // Async so the in-process gateway can answer while the child runs.
+      const r = await execFileAsync('bash', [SCRIPT], {
+        env: {
+          ...process.env,
+          PATH: `${unameDir}:${process.env.PATH}`,
+          TMPDIR: tmp,
+          FPAGENT_BASE_URL: urlOf(gateway),
+        },
+      });
+      out = r.stdout + r.stderr;
+    } catch (e) {
+      out = `${e.stdout ?? ''}${e.stderr ?? ''}`; // the asset download 404s
+    }
+    assert.match(out, /cafebabe/, 'the i386 version should come from the asset name');
+    assert.ok(
+      calls.some((u) => u.includes('fpagent-cafebabe-linux-i386.tar.gz')),
+      'should request the i386 bundle'
+    );
+    assert.ok(
+      !calls.some((u) => u.includes('x86_64')),
+      'should never request another architecture\u2019s bundle'
+    );
+  } finally {
+    fs.rmSync(tmp, { recursive: true, force: true });
+    fs.rmSync(unameDir, { recursive: true, force: true });
+    await stopServer(gateway);
+  }
+});
+
+test('install.sh refuses an unsupported architecture before fetching', async () => {
+  const calls = [];
+  const gateway = await startServer((req, res) => {
+    calls.push(req.url);
+    res.writeHead(404);
+    res.end();
+  });
+  const unameDir = fakeUname('aarch64');
+  const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'fpagent-arch-test-'));
+  try {
+    let out = '';
+    let failed = false;
+    try {
+      const r = await execFileAsync('bash', [SCRIPT], {
+        env: {
+          ...process.env,
+          PATH: `${unameDir}:${process.env.PATH}`,
+          TMPDIR: tmp,
+          FPAGENT_BASE_URL: urlOf(gateway),
+        },
+      });
+      out = r.stdout + r.stderr;
+    } catch (e) {
+      failed = true;
+      out = `${e.stdout ?? ''}${e.stderr ?? ''}`;
+    }
+    assert.equal(failed, true, 'the installer should reject an unsupported host');
+    assert.match(out, /unsupported architecture: aarch64/);
+    assert.equal(calls.length, 0, 'should fail before touching the network');
+  } finally {
+    fs.rmSync(tmp, { recursive: true, force: true });
+    fs.rmSync(unameDir, { recursive: true, force: true });
+    await stopServer(gateway);
+  }
+});
+
 test('install.sh is valid bash', () => {
   execFileSync('bash', ['-n', SCRIPT], { stdio: 'pipe' });
 });