fix(core): cancel prompts when the input stream ends

[MFA-G]

What does this PR do?

When the input stream ends while a prompt is waiting (or has already ended before it starts), prompt() never settles: it only resolves on submit/cancel, and nothing listens for the stream ending. With stdin from /dev/null, in CI or in agent shells, or with piped input that runs out before the last prompt, await confirm(...) hangs and Node exits with code 13 ("Detected unsettled top-level await"), leaving the cursor hidden.

This PR cancels the prompt in that case, so callers get the cancel symbol they already handle with isCancel(). That is the behavior the issue suggests.

• Prompt#prompt() listens for end on the input and runs the same cancel path as Ctrl+C: state = 'cancel', finalize, render, close(). If the stream has already ended (readableEnded), the prompt cancels right away, because end will not be emitted again.
• If the prompt has already been submitted or cancelled, an end event is ignored, and close() removes the listener so nothing leaks to the next prompt that shares stdin.

With the repro from the issue (built locally against this branch):

$ node repro.mjs < /dev/null
...
confirm settled with cancel
text settled with cancel
$ echo $?
0

On main the same command prints Warning: Detected unsettled top-level await and exits with 13.

Closes #615

Type of change

• Bug fix
• Feature
• Refactor (no behavior change)
• Documentation
• Performance improvement
• Tests
• Chore (dependencies, CI, tooling)

Checklist

• pnpm test passes (or targeted tests for my change)
• pnpm format has been run
• I have added/updated tests for my changes (if applicable)
• I have added a changeset

Three new tests are in packages/core/test/prompts/prompt.test.ts: the input ends while a prompt is active, the input ended before the prompt started, and the input ends after a submit (the result must stay the submitted value). The first two time out on main. pnpm test passes (core 174, prompts 618), and pnpm types and biome check are clean.

AI-generated code disclosure

• This PR includes AI-generated code

[changeset-bot]

🦋 Changeset detected

Latest commit: cddd575

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@clack/core	Patch
@clack/prompts	Patch

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[43081j]

seems to make sense