.NET: [Bug]: CosmosDBChatExtensions does not restore ChatHistoryProvider state on deserialize

[rcoccia]

Description

When deserializing a session with ChatClientAgent.DeserializeSessionAsync, the framework passes the serialized ChatHistoryProviderState to ChatHistoryProviderFactory. However, the official CosmosDBChatExtensions factory ignores this state and always creates a new CosmosChatHistoryProvider, which generates a new ConversationId. As a result, conversation history is lost on each deserialize.

Expected:
The factory should use context.SerializedState when present and call CosmosChatHistoryProvider.CreateFromSerializedState(...) to preserve the original ConversationId

Actual:
The factory always creates new CosmosChatHistoryProvider(...), losing the previous ConversationId

Suggested Fix:

options.ChatHistoryProviderFactory = (context, ct) =>

{
    if (context.SerializedState.ValueKind == JsonValueKind.Object)
    {
        return new ValueTask<ChatHistoryProvider>(
            CosmosChatHistoryProvider.CreateFromSerializedState(
                new CosmosClient(accountEndpoint, tokenCredential),
                context.SerializedState,
                databaseId,
                containerId,
                context.JsonSerializerOptions));
    }

    return new ValueTask<ChatHistoryProvider>(
        new CosmosChatHistoryProvider(accountEndpoint, tokenCredential, databaseId, containerId));
};

Code Sample

Error Messages / Stack Traces

Package Versions

Microsoft.Agents.AI 1.0.0-preview.251113.1

.NET Version

.NET 10

Additional Context

No response