Python: Agent(client=FoundryChatClient(...)) type-checks as invalid with ty, runtime works #6938

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   Eduard van Valkenburg (eavanvalkenburg)

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7. github-actions commented on Jul 7, 2026

   

   github-actionsBot

   on Jul 7, 2026 – with GitHub Actions

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   👋 Hi Pamela Fox (@pamelafox) — thanks for the report!

   Your reported ty error (error[invalid-argument-type]: Expected SupportsChatGetResponse[...], found FoundryChatClient[...]) does not reproduce with ty 0.0.21 (your stated version) or ty 0.0.56 against the current v1.10.0 codebase — both pass cleanly on your exact repro snippet. To investigate further we would need: (1) your ty project configuration (any ty.toml, pyproject.toml [tool.ty] settings, or CLI flags you use), (2) the output of pip show agent-framework-core agent-framework-foundry confirming exact installed versions, and (3) whether ty is resolving types from your venv or from source. It's possible your environment is missing the .pyi stub at agent_framework/foundry/__init__.pyi or ty is picking up a different package installation.

   Once you can share the details above, we'll take another look. 🙏
8. eavanvalkenburg commented on Jul 7, 2026

   

   Eduard van Valkenburg (eavanvalkenburg)

   on Jul 7, 2026

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   Hi Pamela Fox (@pamelafox)
   in this line, we specifically check for this:

   agent-framework/python/packages/foundry/tests/foundry/test_foundry_chat_client.py

   Line 159 in c67372f

   assert isinstance(client, SupportsChatGetResponse)

   and when I run ty (v 0.0.46) against the test file everything passes.

   and when I add:

   client = FoundryChatClient(project_client=mock_project, model="test-model")
   
   agent = Agent(client=client, instructions="test agent")

   as a test, it also passes ty. When I run with ty==0.0.21 I also get passing checks. I am looking further, but if you have additional info, let me know!
9. pamelafox commented on Jul 7, 2026

   

   Pamela Fox (pamelafox)

   on Jul 7, 2026

   Last edited by pamelafox

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   Hm, the full file is here:
   https://github.com/Azure-Samples/foundry-hosted-agentframework-demos/blob/main/agents/stage4_foundry_hosted.py

   I get the error both from the ty VS Code extension and my local ty, across all the versions (I just upgraded as well to check 0.56)

   error[invalid-argument-type]: Argument to `Agent.__init__` is incorrect
     --> agents/stage4_foundry_hosted.py:99:9
      |
   99 |         client=client,
      |         ^^^^^^^^^^^^^ Expected `SupportsChatGetResponse[OpenAIChatOptions[None] | (ChatOptions[None] & ChatOptions[Any]) | None | dict[str, bool]]`, found `FoundryChatClient[OpenAIChatOptions[None]]`
      |
   info: type `FoundryChatClient[OpenAIChatOptions[None]]` is not assignable to protocol `SupportsChatGetResponse[OpenAIChatOptions[None] | (ChatOptions[None] & ChatOptions[Any]) | None | dict[str, bool]]`
   info: └── protocol member `get_response` is incompatible
   info: Method defined here
       --> agents/.venv/lib/python3.14/site-packages/agent_framework/_agents.py:1730:9
        |
   1730 |     def __init__(
        |         ^^^^^^^^
   1731 |         self,
   1732 |         client: SupportsChatGetResponse[OptionsCoT],
        |         ------------------------------------------- Parameter declared here
        |
   
10. Eduard van Valkenburg (eavanvalkenburg)

    closed this as completedin #6950on Jul 7, 2026
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12. pamelafox commented on Oct 19, 2026

    

    Pamela Fox (pamelafox)

    on Oct 19, 2026

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    I found what triggers this in my code: passing a plain dict as default_options.

    Agent.__init__ uses one type variable for both arguments:

    client: SupportsChatGetResponse[OptionsCoT],
    default_options: OptionsCoT | None = None,

    When default_options is a dict literal such as {"store": False}, ty includes dict[str, bool] in the solution for OptionsCoT, and then FoundryChatClient[OpenAIChatOptions[None]] no longer matches the expected client type. The dict[str, bool] shows up at the end of the expected type in the error:

    Expected `SupportsChatGetResponse[OpenAIChatOptions[None] | (ChatOptions[None] & ChatOptions[Any]) | None | dict[str, bool]]`, found `FoundryChatClient[OpenAIChatOptions[None]]`
    

    That would explain why the snippet in the original report didn't reproduce: it doesn't pass default_options.

    Code that shows the error

    from agent_framework import Agent
    from agent_framework.foundry import FoundryChatClient
    from azure.identity import DefaultAzureCredential
    
    client = FoundryChatClient(
        project_endpoint="https://example.services.ai.azure.com/api/projects/example",
        model="gpt-5.5",
        credential=DefaultAzureCredential(),
    )
    
    agent = Agent(
        client=client,
        instructions="You are a friendly assistant",
        default_options={"store": False},  # error is reported on `client=` above
    )

    Workaround

    Passing a typed options object fixes the error, and it's still a plain dict at runtime:

    from agent_framework.openai import OpenAIChatOptions
    
    agent = Agent(
        client=client,
        instructions="You are a friendly assistant",
        default_options=OpenAIChatOptions(store=False),
    )

    Environment

    • ty 0.0.89, VS Code ty extension 2026.80.0
    • agent-framework-core 1.21.0, agent-framework-foundry 1.14.1, agent-framework-openai 1.16.0
    • Python 3.14.4

    Caveat: the error appears in the VS Code ty extension (language server). Running ty check from the command line with the same ty version and virtual environment passes for both versions of the snippet, so the CLI may not reproduce it.

    A possible fix in agent-framework: let default_options accept a plain mapping without that type taking part in the type variable that client also uses.

    This comment was written with help from GitHub Copilot.