fix(agent-core-v2): only send prompt_cache_key to official OpenAI endpoints

[creatiVision]

Related Issue

Resolves #2166 (NVIDIA NIM: 400 Validation: Unsupported parameter(s): prompt_cache_key). Related: #2611 (Azure Foundry: 400 Unrecognized request argument supplied: prompt_cache_key).

Supersedes and replaces #2240 and #2761, which are closed in favor of this single reconciled branch.

Problem

Since v0.29.0 (#1970), every OpenAI-compatible provider receives the session prompt_cache_key in the request body. Strictly-validating endpoints (e.g. NVIDIA NIM, Azure Foundry) reject the unknown parameter with HTTP 400, making custom openai / openai_responses providers unusable for agent sessions.

What changed

The field is now only sent when the effective base URL targets the official OpenAI API (api.openai.com or a regional *.api.openai.com variant, or unset → client default):

• Added isOfficialOpenAIBaseUrl() helper in packages/agent-core-v2/src/human/llm/requester/bases/openai-base-url.ts.
• Gated the prompt_cache_key fallback behind it in both the OpenAI chat-completions and Responses bases (openai/format.ts, openai-responses/format.ts). A vendor that supports the field on other hosts keeps encoding it via the cacheKey trait hook (e.g. Kimi), which is unaffected.
• Tests: cache-key.test.ts (official endpoint keeps the key; third-party endpoint omits it) and response-format.test.ts (Responses base omits it for third-party endpoints).

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: 0c0ae57

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-v2	Patch
@moonshot-ai/kimi-code	Patch

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[creatiVision]

Superseded by #2240 — the same reconciled fix lives on fix/latest-with-prompt-cache. Closing this one.

[creatiVision]

Superseded by #2240 — the same reconciled fix lives on fix/latest-with-prompt-cache. Closing this one.