fix(kosong): restore Kimi preserved-thinking sessions

[RealKai42]

Related Issue

No linked issue. The problem was reproduced from exported sessions that could no longer continue after an empty reasoning step.

Problem

Kimi preserved thinking requires reasoning_content on historical assistant messages. Older sessions can contain assistant messages without a ThinkPart because an explicitly empty reasoning step was previously dropped. With thinking.keep set to all, replaying that history repeatedly fails the request instead of allowing the session to continue.

What changed

• At Kimi request serialization only, backfill reasoning_content: "" for assistant history that lacks a ThinkPart when thinking.keep is all and thinking is not disabled.
• Preserve existing empty and non-empty reasoning verbatim, and leave inactive keep modes and non-assistant messages unchanged.
• Keep canonical history untouched so other providers never receive synthesized thinking.
• Mirror the behavior in the v1 and v2 provider paths, including coverage for legacy tool-call and text history, existing reasoning, inactive modes, disabled thinking, and provider-role boundaries.

Validation

• pnpm exec vitest run packages/kosong/test — 49 files, 1220 tests passed.
• pnpm --filter @moonshot-ai/agent-core-v2 test — 237 files, 3361 tests passed.
• Type checks passed for @moonshot-ai/kosong and @moonshot-ai/agent-core-v2.
• pnpm --filter @moonshot-ai/agent-core-v2 run lint:domain passed for 855 files.
• Type-aware lint passed for all changed TypeScript files.

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: 1043041

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@1043041

npx https://pkg.pr.new/@moonshot-ai/kimi-code@1043041

commit: 1043041