fix: ensure Bedrock compliance by separating tool result and conversation blocks in chat history adapter

[ShyamSathish005]

Why are these changes needed?

This PR updates the _convert_to_chat_history method in SKChatCompletionAdapter to ensure that tool result blocks and conversation blocks are never combined in the same turn. If two tool result messages would be consecutive, a dummy user message is inserted to break the turn, fully complying with Bedrock's requirements and preventing the API error.

Fixes intermittent Bedrock ValidationException errors in multi-agent scenarios.
Ensures stable tool use and message handoff for teams of agents using AWS Bedrock models via Semantic Kernel.

Related issue number

Closes #6480

Checks

• [✅ ] I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• [✅ ] I've added tests (if relevant) corresponding to the changes introduced in this PR.
• [ ✅] I've made sure all auto checks have passed.

[victordibia]

@ShyamSathish005 ,

Thanks for the PR.
Can you kindly include a minimum reproducible example in the PR description?
Ideally an example triggers the error and fixed by the _sk_chat_completion_adapter.py update

Thanks.

[ShyamSathish005]

Sure.

[ShyamSathish005]

This PR updates the _convert_to_chat_history method in SKChatCompletionAdapter to ensure strict Bedrock compliance by separating tool result and conversation blocks in the chat history. The adapter now inserts a dummy user message if two tool result messages would otherwise be consecutive, preventing them from being combined in the same turn. This change addresses intermittent ValidationException errors from Bedrock in multi-agent scenarios, ensuring stable tool use and message handoff for agent teams using AWS Bedrock models via Semantic Kernel.

The following example triggers the error before this fix:

Example that triggers the Bedrock ValidationException

from your_package import SKChatCompletionAdapter

chat_history = [
    {"role": "user", "content": "Start"},
    {"role": "tool", "content": "Tool result 1"},
    {"role": "tool", "content": "Tool result 2"},  # Consecutive tool results
    {"role": "assistant", "content": "Response"}
]

adapter = SKChatCompletionAdapter()
try:
    # This would raise a ValidationException before the fix
    converted = adapter._convert_to_chat_history(chat_history)
    print(converted)
except Exception as e:
    print("Error:", e)

#6522 After the fix:
The above code will no longer raise a Bedrock ValidationException. The adapter will insert a dummy user message between consecutive tool results, ensuring compliance and stable operation.