fix(kosong): clamp uncached OpenAI input usage

[morluto]

Related Issue

No linked issue. This is a focused fix for a reproducible OpenAI-compatible usage edge case.

Problem

When a compatible endpoint reports cached-token details but omits the aggregate prompt/input token count, both OpenAI adapters default the aggregate to zero and then subtract the cache count. That produces a negative inputOther, which cancels the reported cache usage when total input is calculated.

Usage projection	Before	After
Reported aggregate input	0	0
Reported cache read	10	10
Derived uncached input	-10	0
Calculated total input	0	10

Official OpenAI usage objects include the aggregate token fields, so this primarily hardens compatibility with partial responses from OpenAI-compatible endpoints.

What changed

• Clamp derived uncached input tokens at zero for Chat Completions and Responses usage parsing.
• Apply the same correction to the legacy and v2 provider implementations.
• Add regressions for cache details reported without aggregate prompt/input totals.
• Preserve the provider-reported cache and output counts unchanged.

Test plan

• pnpm vitest run packages/kosong/test/kimi.test.ts packages/kosong/test/openai-responses.test.ts packages/agent-core-v2/test/kosong/provider/composition.test.ts (239 passed)
• pnpm vitest run --project kosong (1,336 passed)
• pnpm vitest run packages/agent-core-v2/test/agent/mcp/output.test.ts (39 passed)
• pnpm --filter @moonshot-ai/kosong typecheck
• pnpm --filter @moonshot-ai/agent-core-v2 typecheck
• pnpm --filter @moonshot-ai/agent-core-v2 lint:domain
• pnpm --filter @moonshot-ai/kosong build
• pnpm --filter @moonshot-ai/agent-core-v2 build

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: fe59b40

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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