fix serialization issue in streamablehttp mcp tools (#6721)

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The current `StreamableHttpServerParams` has timedelta values that are
not JSON serializable (config.dump_component.model_dump_json()).
This make is unusable in UIs like AGS that expect configs to be
serializable to json,

```python
class StreamableHttpServerParams(BaseModel):
    """Parameters for connecting to an MCP server over Streamable HTTP."""

    type: Literal["StreamableHttpServerParams"] = "StreamableHttpServerParams"

    url: str  # The endpoint URL.
    headers: dict[str, Any] | None = None  # Optional headers to include in requests.
    timeout: timedelta = timedelta(seconds=30)  # HTTP timeout for regular operations.
    sse_read_timeout: timedelta = timedelta(seconds=60 * 5)  # Timeout for SSE read operations.
    terminate_on_close: bool = True
```

This PR uses float for time outs and casts it to timedelta as needed. 

```python
class StreamableHttpServerParams(BaseModel):
    """Parameters for connecting to an MCP server over Streamable HTTP."""

    type: Literal["StreamableHttpServerParams"] = "StreamableHttpServerParams"

    url: str  # The endpoint URL.
    headers: dict[str, Any] | None = None  # Optional headers to include in requests.
    timeout: float = 30.0  # HTTP timeout for regular operations in seconds.
    sse_read_timeout: float = 300.0  # Timeout for SSE read operations in seconds.
    terminate_on_close: bool = True
```

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## Why are these changes needed?

<!-- Please give a short summary of the change and the problem this
solves. -->

## Related issue number

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python/packages/autogen-ext/src/autogen_ext/tools/mcp/_config.py

@@ -1,4 +1,3 @@
-from datetime import timedelta
 from typing import Any, Literal
 
 from mcp import StdioServerParameters
@@ -32,8 +31,8 @@ class StreamableHttpServerParams(BaseModel):
 
     url: str  # The endpoint URL.
     headers: dict[str, Any] | None = None  # Optional headers to include in requests.
-    timeout: timedelta = timedelta(seconds=30)  # HTTP timeout for regular operations.
-    sse_read_timeout: timedelta = timedelta(seconds=60 * 5)  # Timeout for SSE read operations.
+    timeout: float = 30.0  # HTTP timeout for regular operations in seconds.
+    sse_read_timeout: float = 300.0  # Timeout for SSE read operations in seconds.
     terminate_on_close: bool = True
 
 

python/packages/autogen-ext/src/autogen_ext/tools/mcp/_session.py

@@ -32,7 +32,12 @@ async def create_mcp_server_session(
             ) as session:
                 yield session
     elif isinstance(server_params, StreamableHttpServerParams):
-        async with streamablehttp_client(**server_params.model_dump(exclude={"type"})) as (
+        # Convert float seconds to timedelta for the streamablehttp_client
+        params_dict = server_params.model_dump(exclude={"type"})
+        params_dict["timeout"] = timedelta(seconds=server_params.timeout)
+        params_dict["sse_read_timeout"] = timedelta(seconds=server_params.sse_read_timeout)
+
+        async with streamablehttp_client(**params_dict) as (
             read,
             write,
             session_id_callback,  # type: ignore[assignment, unused-variable]
@@ -41,6 +46,6 @@ async def create_mcp_server_session(
             async with ClientSession(
                 read_stream=read,
                 write_stream=write,
-                read_timeout_seconds=server_params.sse_read_timeout,
+                read_timeout_seconds=timedelta(seconds=server_params.sse_read_timeout),
             ) as session:
                 yield session

python/packages/autogen-ext/src/autogen_ext/tools/mcp/_streamable_http.py

@@ -49,7 +49,6 @@ class StreamableHttpMcpToolAdapter(
         .. code-block:: python
 
             import asyncio
-            from datetime import timedelta
             from autogen_ext.models.openai import OpenAIChatCompletionClient
             from autogen_ext.tools.mcp import StreamableHttpMcpToolAdapter, StreamableHttpServerParams
             from autogen_agentchat.agents import AssistantAgent
@@ -62,8 +61,8 @@ class StreamableHttpMcpToolAdapter(
                 server_params = StreamableHttpServerParams(
                     url="https://api.example.com/mcp",
                     headers={"Authorization": "Bearer your-api-key", "Content-Type": "application/json"},
-                    timeout=timedelta(seconds=30),
-                    sse_read_timeout=timedelta(seconds=60 * 5),
+                    timeout=30.0,  # HTTP timeout in seconds
+                    sse_read_timeout=300.0,  # SSE read timeout in seconds (5 minutes)
                     terminate_on_close=True,
                 )