Resuming sessions with tools raises a TypeError exception.

[zavocc]

Trying to make sure the same tools can still be used when resuming sessions, but trying to do so causes an error:

TypeError: Object of type Tool is not JSON serializable

However, passing tools just works fine when using create_session method... same tools, the only thing that changed is the mode of operations (create session or resume session method)

Here is the sample code trying to do so, assuming that first run was successful after using create_session method with tools provided before, then resuming it with same or different set of tools:

import asyncio
import copilot
from pydantic import BaseModel, Field

class ToolGetWeatherParams(BaseModel):
    location: str = Field(..., description="The location to get the weather for.")

@copilot.define_tool(description="Get Weather today")
def tool_get_weather(params: ToolGetWeatherParams) -> str:
    return f"The weather in {params.location} is sunny with a high of 75°F."

async def main():
    client = copilot.CopilotClient()
    await client.start()

    # Note that this works if I use create_session
    session = await client.resume_session({
        "session_id": "test-session-123",
        "tools": [tool_get_weather]
    })
    response = await session.send_and_wait({"prompt": "What is the weather in London?"})
    print(response.data.content)

    await session.destroy()
    
    # Stop
    await client.stop()

asyncio.run(main())

Expected behavior that it should resume session with no errors and can call tools.

[github-actions]

Thank you for reporting this issue, @zavocc!

I've labeled this as a bug affecting the Python SDK. The issue is clear: resume_session fails to serialize Tool objects when tools are passed, while create_session handles this correctly. You've provided excellent detail with error messages, sample code, and expected behavior.

This looks like a serialization handling inconsistency between the two methods that needs to be addressed by the maintainers.

AI generated by Issue Triage Agent

[zavocc]

I tried using low-level method (without pydantic) according to this doc: https://github.com/github/copilot-sdk/blob/main/python/README.md#tools
but it still doesn't work, same problem where Tool is not json serialisable

[abhijitsingh10]

Apply the same tool serialization pipeline in both methods.

Example (illustrative):

def _normalize_tools(self, tools: list[Tool]) -> list[dict]:
return [tool.to_dict() for tool in tools]

Then in both methods:

if "tools" in options:
options["tools"] = self._normalize_tools(options["tools"])

That’s it. One shared helper, zero API changes.

Temporary workaround (until fixed upstream)

If you need this now, you can manually serialize tools the same way create_session does.

Reuse the session’s existing tools (recommended)

If the session already exists and tools were registered during creation:

session = await client.resume_session({
"session_id": "test-session-123"
})

No tools passed → no error → tools remain available.

Manually serialize tools (hacky but works)

If Tool exposes a schema method (often named to_dict() or similar):

session = await client.resume_session({
"session_id": "test-session-123",
"tools": [tool_get_weather.to_dict()]
})

This bypasses the serialization issue entirely.