Interrupt requests can push a queued message through instead of stopping the turn

What

Programs and remote apps that drive Claude Code can send an interrupt request to stop what Claude is doing. That request can now do something else instead:

• New fields: the interrupt request gains two internal fields. send_now asks that waiting messages from you reach the model now, either by moving the blocking work to the background or by stopping the turn. message_uuid names the queued message that was pressed.
• Advertised: support is announced by the interrupt_send_now_v1 capability in the system/init message.
• Handling: when Claude Code runs without its own screen and gets an interrupt naming a pressed queued message, it now pushes that message through instead of stopping the turn.
• Combining requests: when two interrupt requests are merged, send_now is kept only if the earlier one set it, message_uuid is kept only when both refer to the same message, and cancel_queued is carried through as before.
• Recognition: a request counts as send-now when send_now is true and cancel_queued is not.
• Removed: the old paths that answered an interrupt early during a file download, and a turn handoff early, are gone. Messages are now held until the start or result message has been written (writeAfterInit).

Why

This makes a "send now" action possible in remote apps and SDK hosts: a message you queued can reach Claude mid-turn without ending the session.