feat(client): store InitializeResult as initialize_result (#2300)

src/mcp/client/client.py

@@ -19,6 +19,7 @@ from mcp.types import (
     EmptyResult,
     GetPromptResult,
     Implementation,
+    InitializeResult,
     ListPromptsResult,
     ListResourcesResult,
     ListResourceTemplatesResult,
@@ -29,7 +30,6 @@ from mcp.types import (
     ReadResourceResult,
     RequestParamsMeta,
     ResourceTemplateReference,
-    ServerCapabilities,
 )
 
 
@@ -155,9 +155,16 @@ class Client:
         return self._session
 
     @property
-    def server_capabilities(self) -> ServerCapabilities | None:
-        """The server capabilities received during initialization, or None if not yet initialized."""
-        return self.session.get_server_capabilities()
+    def initialize_result(self) -> InitializeResult:
+        """The server's InitializeResult.
+
+        Contains server_info, capabilities, instructions, and the negotiated protocol_version.
+        Raises RuntimeError if accessed outside the context manager.
+        """
+        result = self.session.initialize_result
+        if result is None:  # pragma: no cover
+            raise RuntimeError("Client must be used within an async context manager")
+        return result
 
     async def send_ping(self, *, meta: RequestParamsMeta | None = None) -> EmptyResult:
         """Send a ping request to the server."""

src/mcp/client/session.py

@@ -131,7 +131,7 @@ class ClientSession(
         self._logging_callback = logging_callback or _default_logging_callback
         self._message_handler = message_handler or _default_message_handler
         self._tool_output_schemas: dict[str, dict[str, Any] | None] = {}
-        self._server_capabilities: types.ServerCapabilities | None = None
+        self._initialize_result: types.InitializeResult | None = None
         self._experimental_features: ExperimentalClientFeatures | None = None
 
         # Experimental: Task handlers (use defaults if not provided)
@@ -185,18 +185,19 @@ class ClientSession(
         if result.protocol_version not in SUPPORTED_PROTOCOL_VERSIONS:
             raise RuntimeError(f"Unsupported protocol version from the server: {result.protocol_version}")
 
-        self._server_capabilities = result.capabilities
+        self._initialize_result = result
 
         await self.send_notification(types.InitializedNotification())
 
         return result
 
-    def get_server_capabilities(self) -> types.ServerCapabilities | None:
-        """Return the server capabilities received during initialization.
+    @property
+    def initialize_result(self) -> types.InitializeResult | None:
+        """The server's InitializeResult. None until initialize() has been called.
 
-        Returns None if the session has not been initialized yet.
+        Contains server_info, capabilities, instructions, and the negotiated protocol_version.
         """
-        return self._server_capabilities
+        return self._initialize_result
 
     @property
     def experimental(self) -> ExperimentalClientFeatures: