fix: handle EndOfStream and ClosedResourceError in send_request

Fixes #1717

The `send_request` method only catches `TimeoutError` from the
`response_stream_reader.receive()` call. If `receive()` raises
`EndOfStream` or `ClosedResourceError` (e.g., when the connection
closes unexpectedly), these exceptions propagate without being
caught, potentially leaving `response_or_error` unassigned and
causing an `UnboundLocalError` at the subsequent isinstance check.

This adds explicit handling for these stream closure exceptions,
converting them to `McpError` with `CONNECTION_CLOSED` error code.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kxbnb

src/mcp/shared/session.py

@@ -274,6 +274,10 @@ async def send_request(
                 class_name = request.__class__.__name__
                 message = f"Timed out while waiting for response to {class_name}. Waited {timeout} seconds."
                 raise MCPError(code=REQUEST_TIMEOUT, message=message)
+            except (anyio.EndOfStream, anyio.ClosedResourceError) as e:
+                class_name = request.__class__.__name__
+                message = f"Connection closed while waiting for response to {class_name}: {e}"
+                raise MCPError(code=CONNECTION_CLOSED, message=message)
 
             if isinstance(response_or_error, JSONRPCError):
                 raise MCPError.from_jsonrpc_error(response_or_error)