fix(pi): single-flight managed extension materialization

tests/unit/pi-extension-host.test.ts

@@ -35,6 +35,26 @@ async function post(
 }
 
 describe('managed Pi extension bridge', () => {
+  it('single-flights the shared managed extension for concurrent worker registration', async () => {
+    const root = await mkdtemp(path.join(tmpdir(), 'makelore-pi-extension-concurrent-'));
+    roots.push(root);
+    const host = new PiManagedExtensionHost();
+    hosts.push(host);
+
+    const registrations = await Promise.all(Array.from({ length: 8 }, async (_, index) => (
+      await host.registerWorker({
+        conversationId: `conversation-${index + 1}`,
+        generation: 1,
+        projectId: `project-${index + 1}`,
+        extensionsDir: root,
+      })
+    )));
+
+    expect(new Set(registrations.map(({ extensionPath }) => extensionPath)).size).toBe(1);
+    expect(host.getDiagnostics().registrations).toEqual({ parent: 8, child: 0 });
+    await Promise.all(registrations.map(({ dispose }) => dispose()));
+  });
+
   it('finishes a queued HTTP request while closing a holder and waiter', async () => {
     const root = await mkdtemp(path.join(tmpdir(), 'makelore-pi-extension-close-'));
     roots.push(root);