Keep what an interrupted reply had already committed

[shellicar]

Summary

• Interrupting a reply keeps what Claude had already said, so it can answer questions about it on the next turn.
• Thinking already completed when the interrupt lands is kept too, so the reasoning behind an unfinished answer is not thrown away.
• A tool call still streaming its input is dropped whole.
• An interrupted query records a [Request interrupted by user] message after the reply it cut off.
• Interrupting before anything was committed hands the prompt back to the editor and takes the abandoned exchange off the transcript.
• Cancelling a query no longer reports an error.