feat(agent-core): tighten Write and Edit tool guidance

[chengluyu]

Related Issue

No linked issue; this PR addresses the tool-selection problem described below.

Problem

The file tool prompts did not make the Edit-over-Write rule forceful enough, so the model could choose Write for small edits to existing files. That risks unnecessary full-file overwrites when an exact Edit replacement is the safer tool.

What changed

• Tightened the Write prompt so incremental changes to existing files are explicitly disallowed, including trivial and one-line edits.
• Reworked the Edit prompt into a short description plus bullets that preserve the exact-match, ordering, and line-ending rules.
• Updated prompt assertions so accidental weakening of the guidance is caught.
• Added a changeset for the agent-core prompt change and the CLI bundle.
• Raised the timeout for two git integration tests that exceeded the default 5s timeout under the full monorepo test run.

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 install --frozen-lockfile
• pnpm test
• pnpm --filter @moonshot-ai/agent-core run typecheck
• pnpm --filter @moonshot-ai/kimi-code run typecheck
• pnpm exec oxlint --quiet apps/kimi-code/test/utils/git/git-ls-files.test.ts packages/agent-core/test/tools/edit.test.ts packages/agent-core/test/tools/write.test.ts
• git diff --check origin/main..HEAD && git diff --check
• Read-only diff audit for internal identifiers: no issues found.

[changeset-bot]

🦋 Changeset detected

Latest commit: 03a2733

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

This PR includes changesets to release 2 packages

Name	Type
@moonshot-ai/agent-core	Patch
@moonshot-ai/kimi-code	Patch

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[pkg-pr-new]

pnpm dlx https://pkg.pr.new/@moonshot-ai/kimi-code@03a2733

npx https://pkg.pr.new/@moonshot-ai/kimi-code@03a2733

commit: 03a2733