fix: isolate concurrent OpenCode chat runs

tests/unit/opencode-manager.test.ts

@@ -105,6 +105,43 @@ describe('OpencodeManager', () => {
     expect(manager.getStatus()).not.toBe(status);
   });
 
+  it('exposes a stable generation that rolls over only when a new runtime starts', async () => {
+    const { children, spawn } = createSpawnHarness();
+    const manager = new OpencodeManager({
+      port: 4351,
+      binPath: 'C:\\NianCode\\opencode.exe',
+      findPortOwner: vi.fn().mockResolvedValue(null),
+      spawn,
+    });
+
+    expect(manager.getRuntimeGeneration()).toBe(0);
+
+    const initialStart = manager.start();
+    await vi.waitFor(() => expect(children).toHaveLength(1));
+    expect(manager.getRuntimeGeneration()).toBe(1);
+    expect(manager.getRuntimeGenerationProvenance()).toBe('starting');
+    children[0].stdout.emit(
+      'data',
+      Buffer.from('opencode server listening on http://127.0.0.1:4351\n'),
+    );
+    await initialStart;
+    expect(manager.getRuntimeGeneration()).toBe(1);
+    expect(manager.getRuntimeGenerationProvenance()).toBe('fresh');
+    expect(manager.getRuntimeGeneration()).toBe(1);
+
+    const restart = manager.restart();
+    children[0].emit('exit', 0);
+    await vi.waitFor(() => expect(children).toHaveLength(2));
+    children[1].stdout.emit(
+      'data',
+      Buffer.from('opencode server listening on http://127.0.0.1:4351\n'),
+    );
+    await restart;
+
+    expect(manager.getRuntimeGeneration()).toBe(2);
+    expect(manager.getRuntimeGenerationProvenance()).toBe('fresh');
+  });
+
   it('falls back to an ephemeral port when the preferred port has an unhealthy listener', async () => {
     const { children, calls, spawn } = createSpawnHarness();
     const preferredPort = 4340;
@@ -429,6 +466,7 @@ describe('OpencodeManager', () => {
       port: 4329,
       url: 'http://127.0.0.1:4329',
     });
+    expect(manager.getRuntimeGenerationProvenance()).toBe('attached');
     expect(logWarn).toHaveBeenCalledWith(
       '[opencode-runtime] Attached to an existing server; newly generated provider config may not be active',
       expect.objectContaining({