Treat unawaited coroutine warnings as errors in tests

Add pytest filterwarnings to catch unawaited coroutine warnings as
errors. Fix the underlying issue in _await_with_session_monitoring
where a coroutine was not closed before raising when session task
was already done.

pyproject.toml

@@ -110,6 +110,9 @@ filterwarnings = [
     # Suppress OAuth in-memory token storage warnings in tests
     # Tests intentionally use ephemeral storage; this warning is for end users
     "ignore:Using in-memory token storage:UserWarning",
+    # Treat unawaited coroutine warnings as errors - these are almost always bugs
+    "error:coroutine .* was never awaited:RuntimeWarning",
+    "error:Exception ignored in.*coroutine:pytest.PytestUnraisableExceptionWarning",
 ]
 timeout = 5
 env = [

src/fastmcp/client/client.py

@@ -686,6 +686,8 @@ class Client(Generic[ClientTransportT]):
 
         # If session task already failed, raise immediately
         if session_task.done():
+            # Close the coroutine to avoid "was never awaited" warning
+            coro.close()
             exc = session_task.exception()
             if exc:
                 raise exc