Fix client meta forwarding, ClientNotification construction, and v1 test idioms for SDK v2

fastmcp_slim/fastmcp/client/client.py

@@ -809,14 +809,12 @@ class Client(
         reason: str | None = None,
     ) -> None:
         """Send a cancellation notification for an in-progress request."""
-        notification = mcp_types.ClientNotification(
-            root=mcp_types.CancelledNotification(
-                method="notifications/cancelled",
-                params=mcp_types.CancelledNotificationParams(
-                    request_id=request_id,
-                    reason=reason,
-                ),
-            )
+        notification = mcp_types.CancelledNotification(
+            method="notifications/cancelled",
+            params=mcp_types.CancelledNotificationParams(
+                request_id=request_id,
+                reason=reason,
+            ),
         )
         await self.session.send_notification(notification)
 

fastmcp_slim/fastmcp/client/mixins/tools.py

@@ -160,8 +160,14 @@ class ClientToolsMixin:
         ) as span:
             logger.debug(f"[{self.name}] called call_tool: {name}")
 
-            # Inject trace context into meta for propagation to server
+            # Inject trace context into meta for propagation to server.
+            # SDK v2: request `_meta` is `RequestParamsMeta` (a TypedDict), not
+            # the old `RequestParams.Meta` nested model.
             propagated_meta = inject_trace_context(meta)
+            request_meta = cast(
+                "mcp_types.RequestParamsMeta | None",
+                propagated_meta if propagated_meta else None,
+            )
 
             result = await self._await_with_session_monitoring(
                 self.session.call_tool(
@@ -169,7 +175,7 @@ class ClientToolsMixin:
                     arguments=arguments,
                     read_timeout_seconds=normalize_timeout_to_seconds(timeout),
                     progress_callback=progress_handler or self._progress_handler,
-                    meta=propagated_meta if propagated_meta else None,
+                    meta=request_meta,
                 )
             )
 
@@ -365,7 +371,7 @@ class ClientToolsMixin:
         # Use RootModel with Union to handle both response types (SDK calls model_validate)
         wrapped_result = await self._await_with_session_monitoring(
             self.session.send_request(
-                request=request,  # type: ignore[arg-type]  # ty:ignore[invalid-argument-type]
+                request=request,  # type: ignore[arg-type]
                 result_type=ToolTaskResponseUnion,
             )
         )

tests/client/client/test_client.py

@@ -94,12 +94,13 @@ async def test_call_tool_with_meta():
         assert context.request_context is not None
         meta = context.request_context.meta
 
-        # Return the metadata as a dict
+        # Return the metadata as a dict. Under SDK v2 the lifted request meta
+        # is a plain dict, so custom fields are read by key.
         if meta is not None:
             return {
                 "has_meta": True,
-                "user_id": getattr(meta, "user_id", None),
-                "trace_id": getattr(meta, "trace_id", None),
+                "user_id": meta.get("user_id"),
+                "trace_id": meta.get("trace_id"),
             }
         return {"has_meta": False}
 

tests/client/sampling/handlers/test_anthropic_handler.py

@@ -18,7 +18,6 @@ from mcp_types import (
     ToolResultContent,
     ToolUseContent,
 )
-from pydantic import AnyUrl
 
 from fastmcp.client.sampling.handlers.anthropic import (
     AnthropicSamplingHandler,
@@ -387,7 +386,7 @@ def test_convert_messages_raises_on_unsupported_content_type():
     embedded = EmbeddedResource(
         type="resource",
         resource=TextResourceContents(
-            uri=AnyUrl("file:///test.txt"), text="hello", mime_type="text/plain"
+            uri="file:///test.txt", text="hello", mime_type="text/plain"
         ),
     )
     # Must be inside a list content — single-content messages hit a

tests/client/sampling/handlers/test_openai_handler.py

@@ -27,7 +27,6 @@ from openai.types.chat import (
     ChatCompletionUserMessageParam,
 )
 from openai.types.chat.chat_completion import Choice
-from pydantic import AnyUrl
 
 from fastmcp.client.sampling.handlers.openai import (
     OpenAISamplingHandler,
@@ -331,7 +330,7 @@ def test_convert_messages_raises_on_unsupported_content_type():
     embedded = EmbeddedResource(
         type="resource",
         resource=TextResourceContents(
-            uri=AnyUrl("file:///test.txt"), text="hello", mime_type="text/plain"
+            uri="file:///test.txt", text="hello", mime_type="text/plain"
         ),
     )
     msg = SamplingMessage.model_construct(

tests/test_compat.py

@@ -1,5 +1,6 @@
 """Tests for the MCP SDK v2 camelCase compatibility bridge (fastmcp._compat)."""
 
+import datetime
 import warnings
 
 import mcp_types
@@ -7,6 +8,8 @@ import pytest
 from mcp import MCPError as SDKMCPError
 
 import fastmcp._compat as _compat
+from fastmcp import Client, FastMCP
+from fastmcp.client.transports import FastMCPTransport
 from fastmcp.exceptions import FastMCPDeprecationWarning, MCPError, McpError
 
 
@@ -184,3 +187,39 @@ class TestExceptionAlias:
     def test_except_mcp_error_catches_sdk_raised(self):
         with pytest.raises(McpError):
             raise SDKMCPError(code=-32000, message="boom")
+
+
+class TestClientBehaviorCompat:
+    """Behavior compat checklist (design decision D)."""
+
+    @pytest.fixture
+    def server(self):
+        srv = FastMCP("BehaviorServer")
+
+        @srv.tool
+        def echo(x: str) -> str:
+            return x
+
+        return srv
+
+    @pytest.mark.parametrize(
+        "timeout",
+        [5, 5.0, datetime.timedelta(seconds=5), None],
+    )
+    async def test_client_accepts_timedelta_or_float_timeout(self, server, timeout):
+        client = Client(transport=FastMCPTransport(server), timeout=timeout)
+        async with client:
+            result = await client.call_tool("echo", {"x": "hi"})
+        assert result.data == "hi"
+
+    async def test_ping_returns_bool(self, server):
+        client = Client(transport=FastMCPTransport(server))
+        async with client:
+            result = await client.ping()
+        assert result is True
+
+    async def test_session_id_none_safe(self, server):
+        # In-memory transport has no HTTP session id; must return None, not raise.
+        client = Client(transport=FastMCPTransport(server))
+        async with client:
+            assert client.transport.get_session_id() is None