feat: install.sh + auto-update checker for CLI

- tools/install.sh: standalone installer/upgrader, curl-pipe safe
  (main() wrapper, process.argv instead of stdin, mkdir -p prefix)
- packages/mosaic/src/runtime/update-checker.ts: version check module
  with 1h cache at ~/.cache/mosaic/update-check.json
- CLI startup: non-blocking background update check on every invocation
- 'mosaic update' command: explicit check + install (--check for CI)
- session-start.sh: warns agents when CLI is outdated
- Proper semver comparison including pre-release precedence
- eslint: allow __tests__ in packages/mosaic for projectService

packages/cli/src/cli.ts

@@ -10,6 +10,14 @@ import { registerPrdyCommand } from './commands/prdy.js';
 const _require = createRequire(import.meta.url);
 const CLI_VERSION: string = (_require('../package.json') as { version: string }).version;
 
+// Fire-and-forget update check at startup (non-blocking, cached 1h)
+try {
+  const { backgroundUpdateCheck } = await import('@mosaic/mosaic');
+  backgroundUpdateCheck();
+} catch {
+  // Silently ignore — update check is best-effort
+}
+
 const program = new Command();
 
 program.name('mosaic').description('Mosaic Stack CLI').version(CLI_VERSION);
@@ -297,6 +305,52 @@ if (qrCmd !== undefined) {
   program.addCommand(qrCmd as unknown as Command);
 }
 
+// ─── update ─────────────────────────────────────────────────────────────
+
+program
+  .command('update')
+  .description('Check for and install Mosaic CLI updates')
+  .option('--check', 'Check only, do not install')
+  .action(async (opts: { check?: boolean }) => {
+    const { checkForUpdate, formatUpdateNotice } = await import('@mosaic/mosaic');
+    const { execSync } = await import('node:child_process');
+
+    console.log('Checking for updates…');
+    const result = checkForUpdate({ skipCache: true });
+
+    if (!result.latest) {
+      console.error('Could not reach the Mosaic registry.');
+      process.exit(1);
+    }
+
+    console.log(`  Installed: ${result.current || '(none)'}`);
+    console.log(`  Latest:    ${result.latest}`);
+
+    if (!result.updateAvailable) {
+      console.log('\n✔ Up to date.');
+      return;
+    }
+
+    const notice = formatUpdateNotice(result);
+    if (notice) console.log(notice);
+
+    if (opts.check) {
+      process.exit(2); // Signal to callers that an update exists
+    }
+
+    console.log('Installing update…');
+    try {
+      execSync(
+        'npm install -g @mosaic/cli@latest --registry=https://git.mosaicstack.dev/api/packages/mosaic/npm/',
+        { stdio: 'inherit', timeout: 60_000 },
+      );
+      console.log('\n✔ Updated successfully.');
+    } catch {
+      console.error('\nUpdate failed. Try manually: bash tools/install.sh');
+      process.exit(1);
+    }
+  });
+
 // ─── wizard ─────────────────────────────────────────────────────────────
 
 program