fix(hooks): log external command failures

[030611]

Related Issue

Resolve #2766

Problem

External hooks fail open by design, but command launch errors, timeouts, and unexpected non-zero exits currently leave no diagnostic. This makes a broken hook configuration look the same as a hook that was never triggered.

What changed

• emit a warning through the existing diagnostic logger in both hook engines
• include the hook event, configured command, exit status or timeout state, and the first stderr line
• preserve fail-open behavior and keep exit code 2 as an intentional block without a warning
• add regression coverage for unexpected failures and intentional blocks

Validation

• TypeScript checks for agent-core and agent-core-v2
• agent-core-v2 import-boundary check
• focused hook suites: 101 passed, 6 skipped
• new diagnostics regressions: 4 passed

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.

[changeset-bot]

🦋 Changeset detected

Latest commit: 2a27472

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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