Thought / Reasoning messages missing in events

[bastiandg]

Is your feature request related to a problem? Please describe.

This is a follow-up to #1489.

As described in the issue, when setting reasoning configuration and activate the planner, no thinking messages can be found in the events.

MODEL_CLAUDE_SONNET = "anthropic/claude-sonnet-4-20250514"

root_agent = Agent(
    model=LiteLlm(model=MODEL_CLAUDE_SONNET),
    name='root_agent',
    instruction="""answer user questions""",
    planner=BuiltInPlanner(
        thinking_config=types.ThinkingConfig(
            include_thoughts=True,
        ),
    ),
)

Describe the solution you'd like

The solution is to forward the reasoning / thought messages from LiteLlm to the adk session events array.

Describe alternatives you've considered

As a workaround one could use a thinking mcp https://github.com/modelcontextprotocol/servers/tree/main/src/sequentialthinking .
This is probably less performant then the native reasoning capabilities of llms.