The wait tool's prompt runs off-loop on a worker thread, but its read polls
select/msvcrt, so it can act on a cancel: the SIGINT target now sets a flag the
reader checks between polls and raises PromptCancelledError with, which the tool
reports as "cancelled by user" while the turn continues. run_prompt_async /
run_cancellable_prompt_async hand the matching hook to the CLI guard; a stale
cancel never leaks into the next prompt read.
Add process-wide prompting backends for interactive human I/O; wire CLI
limit/confirm/workspace prompts through it. Expose ask_user, choose_user,
and form_user under tools/chat and include them in DEFAULT_TOOLS.
NCBM