fix(coding-runtime): close Pi extension lifecycle races

tests/unit/pi-extension-ui-projector.test.ts

@@ -40,5 +40,15 @@ describe('Pi extension UI projector', () => {
     expect(projector.getDiagnostics()).toEqual([{
       method: 'setWidget', reason: 'unsupported-ui-method',
     }]);
+    for (let index = 0; index < 1_000; index += 1) {
+      projector.project('conversation-a', 1, 'run-1', {
+        type: 'extension_ui_request', id: `unknown-${index}`, method: `unknown-${index}`,
+      });
+    }
+    const diagnostics = projector.getDiagnostics();
+    expect(diagnostics).toHaveLength(256);
+    expect(diagnostics.at(-1)).toEqual({
+      method: 'unknown-999', reason: 'invalid-ui-payload',
+    });
   });
 });