Add docstring info for cancellable and add TODO note for initialised which states that initialised is not cancellable as per https://modelcontextprotocol.io/specification/2025-03-26/basic/utilities/cancellation

Author: davemssavage

src/mcp/client/session.py

@@ -140,6 +140,11 @@ async def initialize(self) -> types.InitializeResult:
                 )
             ),
             types.InitializeResult,
+            # TODO should set a request_read_timeout_seconds as per
+            # guidance from BaseSession.send_request not obvious
+            # what subsequent process should be, refer the following
+            # specification for more details
+            # https://modelcontextprotocol.io/specification/2025-03-26/basic/utilities/cancellation
             cancellable=False,
         )
 

src/mcp/shared/session.py

@@ -229,6 +229,18 @@ async def send_request(
         response contains an error. If a request read timeout is provided, it
         will take precedence over the session read timeout.
 
+        If cancellable is set to False then the request will wait
+        request_read_timeout_seconds to complete and ignore any attempt to
+        cancel via the anyio.CancelScope within which this method was called.
+
+        If cancellable is set to True (default) if the anyio.CancelScope within
+        which this method was called is cancelled it will generate a
+        CancelationNotfication and send this to the server which should then abort
+        the task however this is not guaranteed.
+
+        For further information on the CancelNotification flow refer to
+        https://modelcontextprotocol.io/specification/2025-03-26/basic/utilities/cancellation
+
         Do not use this method to emit notifications! Use send_notification()
         instead.
         """