ClientCitation deserialization fails when Copilot Studio citation contains @id: "ClientCitation" object has no field "at_id" #595

Summary

When using the Microsoft Agents SDK with a signed-in Microsoft user to invoke a Copilot Studio agent, some Copilot Studio responses contain citations with an @id property.

Those responses fail during Activity deserialization with:

entities.citation.0
Value error, "ClientCitation" object has no field "at_id"

The Copilot Studio request itself succeeds and a response is returned. The exception occurs while the Python SDK is deserializing the returned Activity.

The issue can also be reproduced locally without a Microsoft tenant, authentication, Copilot Studio, or any network request.

Environment

Originally observed with:

microsoft-agents-copilotstudio-client==1.5.0
microsoft-agents-activity==1.5.0
pydantic==2.13.4
Python 3.14

I also tested after upgrading to:

microsoft-agents-copilotstudio-client==1.7.0

and the same ClientCitation / at_id exception is still reproduced.

Reproduction repository

A standalone reproduction is available here:

https://github.com/abdurrafay0610/microsoft-agents-activity-sdk-issue-recreation

The repository contains the minimal reproduction, Activity-level reproduction, requirements, and additional diagnostic information.

To reproduce:

git clone https://github.com/abdurrafay0610/microsoft-agents-activity-sdk-issue-recreation.git
cd microsoft-agents-activity-sdk-issue-recreation

pip install -r requirements.txt

python reproduce.py
python reproduce_activity.py

No Microsoft credentials, tenant, or Copilot Studio agent are required for the standalone reproduction.

Input that triggers the failure

The relevant portion of the citation returned by Copilot Studio has this shape:

{
  "@type": "Claim",
  "@id": "turn16search0",
  "position": 1,
  "appearance": {
    "@type": "DigitalDocument",
    "name": "Example citation"
  }
}

The important property is:

"@id": "turn16search0"

SDK deserialization path

microsoft-agents-copilotstudio-client receives the Copilot Studio SSE Activity response in:

microsoft_agents.copilotstudio.client.copilot_client.CopilotClient.post_request()

The Activity JSON is then passed to:

Activity.model_validate_json(activity_data)

During Activity validation, the citation is deserialized as:

microsoft_agents.activity.entity.ai_entity.ClientCitation

ClientCitation uses _SchemaMixin.

The relevant validation helper is:

microsoft_agents.activity.entity._schema_mixin.validate_schema_model

When @id is present in the input, the helper attempts:

setattr(model, "at_id", data["@id"])

However, ClientCitation defines:

at_type
position
appearance

and does not define an at_id field.

The assignment therefore results in:

Value error, "ClientCitation" object has no field "at_id"

Documentation / implementation mismatch

The _SchemaMixin validator describes its behavior as handling @type, @context, and @id when those properties are defined in the destination type.

However, for @id, the implementation attempts to assign at_id when the property is present in the input, without first establishing that the destination model defines at_id.

For ClientCitation, the destination model does not define that field.

Expected behavior

A Copilot Studio Activity containing a citation with the returned @id property should be deserialized without the SDK raising an exception.

Actual behavior

Activity deserialization fails with:

entities.citation.0
Value error, "ClientCitation" object has no field "at_id"

This prevents the application from consuming an otherwise successfully returned Copilot Studio response.

Additional details

The full failure path and standalone examples are documented in the reproduction repository:

https://github.com/abdurrafay0610/microsoft-agents-activity-sdk-issue-recreation

One thing I would definitely fix before submitting is the `repro.py` → `reproduce.py` filename mismatch, because otherwise the first thing a Microsoft maintainer sees when following the instructions is an unrelated `No such file` error.