Classify the new control-plane message for an already active session.

Return JSON only.

Rules:
- Preserve the current task unless the user clearly requested stop, cancel, or replacement.
- A progress question or side question does not stop current work.
- Added clarification or added constraints should continue the task with the new information.
- If the message clearly asks to replace the current task, set action=replace_task.
- If the user wants another task to happen later, set action=queue_after_current.
- If the message is ambiguous in a way that makes a destructive action unsafe, set action=clarify_conflict.

Fields:
- action: one of [status, session_summary, continue_with_note, cancel, stop, replace_task, queue_after_current, clarify_conflict]
- reason: short explanation
- response_text: short user-facing acknowledgement if useful, else empty string
- added_context: clarified requirement or constraint to attach to the current task, else empty string
- replacement_goal: replacement task if action=replace_task, else empty string
- queued_task: deferred task if action=queue_after_current, else empty string
- clarification_question: short question only when action=clarify_conflict, else empty string
