fix(agent-core-v2): revalidate file freshness when the scheduled write starts

[jangjoe]

Related Issue

Follow-up to #3096 — addresses the P1 review finding left unresolved there (Codex review on the stale-guard PR).

Problem

The Edit/Write staleness check ran during tool-call preparation, before the batch scheduler started any task. A file modified after that check — while the write waited behind a conflicting tool call or a user approval prompt — was overwritten without detection.

What changed

• Added an onExecuteTool ordered hook to the agent-core-v2 tool executor that runs inside the scheduled task, directly around the physical tool execution (i.e. after conflicting predecessors have completed).
• The stale guard now revalidates Edit/Write against the recorded mtime at that point and vetoes with outcome 'vetoed' when the file changed since the last read; mtime recording for Read/Edit/Write also moved into the task, so same-batch sequences (Read→Edit, consecutive writes) see the predecessor's record deterministically.
• The prepare-time check stays as early feedback ahead of approval prompts.
• Tests: staleGuard unit tests now exercise the execution-time path (veto after a post-prepare modification, same-batch ordering, failed-read veto); executor tests cover the new seam (middleware ordering across conflicting tasks, run-time veto, and the no-result guard rail).

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue (external PRs: the issue must have a maintainer's /approve).
• 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: 879b404

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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