Side questions: hosts can now ask the running session an out-of-band question

What

• A new side_question control request lets an embedding host (an app or SDK hosting a Claude Code session) ask the running session a question outside the normal conversation flow, including a history of prior question/response pairs.
• The host must supply an onSideQuestion callback to answer these questions, and can report progress while working on an answer.
• Each side question is tracked and cancellable: requests are keyed by request ID with an abort signal, and duplicate deliveries for the same request are ignored.
• If nothing answers within a deadline (660000ms, about 11 minutes), Claude Code returns a synthetic "no answer available" response instead of hanging.
• A new side_question telemetry event records when this feature is used.

Why This lets a host application (for example a remote or cloud session, or an SDK-based integration) pull information from a running Claude Code session without interrupting it, while making sure a slow or missing host answer can't stall the session indefinitely.