fix(web): fall back to session abort for stale prompts

[wbxl2000]

Related Issue

No linked issue. This fixes a web chat stop action race observed during streaming.

Problem

When the web client held a stale prompt_id, prompt-level abort could return aborted: false. The client treated that as handled and did not try the session-level abort fallback, so clicking Stop could appear to do nothing while the session was still running.

What changed

• Fall back to session-level abort when prompt-level abort reports the cached prompt is missing or already completed.
• Clear the stale cached prompt id before falling back.
• Add regression coverage for stale prompt abort and successful prompt abort paths.
• Add a patch changeset for the bundled web fix.

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update.

Verification:

• pnpm --filter @moonshot-ai/kimi-web typecheck
• pnpm --filter @moonshot-ai/kimi-web exec vitest run --reporter=verbose
• pnpm --filter @moonshot-ai/kimi-web build
• git diff --check origin/main..HEAD
• Read-only diff audit: No actionable findings.

Docs: no docs update needed; this restores the existing web Stop behavior without adding a new user-facing command or configuration.

[changeset-bot]

🦋 Changeset detected

Latest commit: 42deaa0

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

This PR includes changesets to release 1 package

Name	Type
@moonshot-ai/kimi-code	Patch

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[pkg-pr-new]

pnpm dlx https://pkg.pr.new/@moonshot-ai/kimi-code@42deaa0

npx https://pkg.pr.new/@moonshot-ai/kimi-code@42deaa0

commit: 42deaa0