auto_decide.build_auto_decisions (3): produces one decision per
action_request entry, defaults to one decision for legacy scalar
interrupts, and skips malformed interrupts silently so a misbehaving
tool can't take down the whole agent_task step.
finalize.extract_final_assistant_message (4): string-content AIMessage
returned verbatim, list-of-parts content concatenated (skipping
non-text parts like tool_use), walks back past trailing ToolMessages
to find the last AIMessage, and returns None when no extractable text
is present (so callers can branch on silence vs. empty).
7 tests, pure unit.
