fix: revert lax coverage pragmas and cleanup identified covered blocks

Author: RJ Lopez

src/mcp/client/session_group.py

@@ -146,7 +146,7 @@ def __init__(
         self._session_exit_stacks = {}
         self._component_name_hook = component_name_hook
 
-    async def __aenter__(self) -> Self:  # pragma: lax no cover
+    async def __aenter__(self) -> Self:
         # Enter the exit stack only if we created it ourselves
         if self._owns_exit_stack:
             await self._exit_stack.__aenter__()
@@ -157,7 +157,7 @@ async def __aexit__(
         _exc_type: type[BaseException] | None,
         _exc_val: BaseException | None,
         _exc_tb: TracebackType | None,
-    ) -> bool | None:  # pragma: lax no cover
+    ) -> bool | None:
         """Closes session exit stacks and main exit stack upon completion."""
 
         # Only close the main exit stack if we created it
@@ -237,13 +237,13 @@ async def disconnect_from_server(self, session: mcp.ClientSession) -> None:
             for name in component_names.tools:
                 if name in self._tools:  # pragma: no branch
                     del self._tools[name]
-                if name in self._tool_to_session:  # pragma: lax no cover
+                if name in self._tool_to_session:  # pragma: no branch
                     del self._tool_to_session[name]
 
         # Clean up the session's resources via its dedicated exit stack
         if session_known_for_stack:
-            session_stack_to_close = self._session_exit_stacks.pop(session)  # pragma: lax no cover
-            await session_stack_to_close.aclose()  # pragma: lax no cover
+            session_stack_to_close = self._session_exit_stacks.pop(session)  # pragma: no cover
+            await session_stack_to_close.aclose()  # pragma: no cover
 
     async def connect_with_session(
         self, server_info: types.Implementation, session: mcp.ClientSession
@@ -323,7 +323,7 @@ async def _establish_session(
             await self._exit_stack.enter_async_context(session_stack)
 
             return result.server_info, session
-        except Exception:  # pragma: lax no cover
+        except Exception:
             # If anything during this setup fails, ensure the session-specific
             # stack is closed.
             await session_stack.aclose()

src/mcp/shared/session.py

@@ -451,7 +451,7 @@ async def _handle_session_message(message: SessionMessage) -> None:
                     try:
                         await stream.send(JSONRPCError(jsonrpc="2.0", id=id, error=error))
                         await stream.aclose()
-                    except Exception:  # pragma: lax no cover
+                    except Exception:
                         # Stream might already be closed
                         pass
                 self._response_streams.clear()

tests/client/test_session_group.py

@@ -5,9 +5,9 @@
 import sys
 from unittest import mock
 
-if sys.version_info < (3, 11):  # pragma: lax no cover
+if sys.version_info < (3, 11):  # pragma: no cover
     from exceptiongroup import BaseExceptionGroup
-else:  # pragma: lax no cover
+else:  # pragma: no cover
     BaseExceptionGroup = ExceptionGroup  # type: ignore # noqa: F821
 
 import httpx
@@ -449,7 +449,7 @@ async def test_unreachable_streamable_http_error_is_catchable() -> None:
             except BaseException as inner:
                 # Expected post-fix: real ConnectError lands here.
                 caught = inner
-    except BaseException as outer:  # pragma: lax no cover
+    except BaseException as outer:  # pragma: no cover
         # If we land here, the error escaped past the inner handler --
         # that is the regression case (masking RuntimeError surfacing
         # from __aexit__ instead of the real ConnectError propagating).