feat: Integrate Pydantic v2 compatibility patches into ADK web server

- Import patch_types_for_pydantic_v2 and create_robust_openapi_function
- Apply compatibility patches before FastAPI app creation
- Replace default OpenAPI generation with robust error-handling version
- Add logging for patch application status and OpenAPI integration
- Ensures Swagger UI works correctly with Pydantic v2 by handling:
  * MCP ClientSession schema generation issues
  * types.GenericAlias compatibility problems
  * httpx.Client schema generation errors
  * Recursion errors in complex model schemas

This integration enables Swagger UI functionality while maintaining
backward compatibility and providing comprehensive error handling.

Author: mmphego

src/google/adk/cli/adk_web_server.py

@@ -94,6 +94,7 @@
 from .utils.base_agent_loader import BaseAgentLoader
 from .utils.shared_value import SharedValue
 from .utils.state import create_empty_state
+from ..utils.pydantic_v2_compatibility import patch_types_for_pydantic_v2, create_robust_openapi_function
 
 logger = logging.getLogger("google_adk." + __name__)
 
@@ -686,6 +687,13 @@ async def internal_lifespan(app: FastAPI):
     tracer_provider = trace.get_tracer_provider()
     register_processors(tracer_provider)
 
+    # Apply Pydantic v2 compatibility patches before creating FastAPI app
+    patches_applied = patch_types_for_pydantic_v2()
+    if patches_applied:
+      logger.info("Pydantic v2 compatibility patches applied successfully")
+    else:
+      logger.warning("Pydantic v2 compatibility patches could not be applied")
+
     # Run the FastAPI server.
     app = FastAPI(lifespan=internal_lifespan)
 
@@ -698,6 +706,10 @@ async def internal_lifespan(app: FastAPI):
           allow_headers=["*"],
       )
 
+    # Replace default OpenAPI function with robust version
+    app.openapi = create_robust_openapi_function(app)
+    logger.info("Robust OpenAPI generation enabled with Pydantic v2 error handling")
+
     @app.get("/list-apps")
     async def list_apps() -> list[str]:
       return self.agent_loader.list_agents()