ToolSearch / MCP tool_reference messages poison session on api.kimi.com/coding/ and cause persistent HTTP 400 invalid_request_error

Description

When using the Anthropic-compatible Kimi Code endpoint at https://api.kimi.com/coding/, sessions appear to break permanently after ToolSearch introduces MCP tool_reference messages into the conversation context.

The provider then starts returning:

HTTP 400
invalid_request_error: Invalid request Error

Once the session contains tool_reference content, follow-up requests continue to fail until a new session is started.

This looks like a provider-side schema / content-type compatibility issue rather than a generic tool failure.

What version of Kimi Code CLI is running?

Observed across:

• 2.1.123
• 2.1.138

Which open platform/subscription were you using?

api.kimi.com/coding/ (Kimi Code subscription / Anthropic-compatible endpoint)

Which model were you using?

Kimi Code model via api.kimi.com/coding/.

What platform is your computer?

macOS / Darwin arm64

What issue are you seeing?

A failing session and a healthy session were compared side by side.

Problematic session:

• Real API 400 errors: 5
• ToolSearch calls: 1
• MCP tool_reference messages: present
• Native tools like Agent/Bash: normal
• Claude Code version: issue persisted from 2.1.123 to 2.1.138

Healthy session:

• Real API 400 errors: 0
• ToolSearch calls: 0
• MCP tool_reference messages: absent
• Native tools like Agent/Bash: normal
• Claude Code version: 2.1.138

Suspected failure chain:

1. Assistant calls ToolSearch
2. ToolSearch returns 3 MCP Playwright tool references
3. Those tool_reference items are added to the conversation context
4. The provider gateway encounters an unsupported / unrecognized content type while parsing the request
5. The request fails with HTTP 400 invalid_request_error
6. Because the bad content remains in context, follow-up requests continue to fail

What steps can reproduce the bug?

1. Use https://api.kimi.com/coding/ in an Anthropic-compatible coding client
2. Start a fresh session
3. Invoke ToolSearch so the tool returns MCP tool references
4. Let those tool_reference messages enter the conversation history
5. Send the next normal assistant/user turn
6. Observe HTTP 400 invalid_request_error: Invalid request Error

What is the expected behavior?

The provider should either:

• fully support tool_reference / MCP-related message content in the conversation schema, or
• safely ignore / normalize unsupported content instead of permanently poisoning the session.

A session should not become unrecoverable just because ToolSearch returned MCP references.

Additional information

What seems ruled out:

• Not ordinary tool usage in general, because native tools continued to work in healthy sessions
• Not purely a client-version issue, because the correlation is with tool_reference presence, not just CLI version

Please investigate:

• schema compatibility for tool_reference content in api.kimi.com/coding/
• provider gateway parsing for MCP-related message content
• fallback behavior for unknown content types
• support status for ToolSearch / MCP / tool_reference under the Anthropic-compatible endpoint

I can provide redacted logs / context snippets if needed.

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中文补充：

当 ToolSearch / MCP 返回的 tool_reference 被写入上下文后，api.kimi.com/coding/ 后续请求会开始持续返回 400，像是 provider 网关不认识这种消息内容类型。一旦上下文被污染，这个 session 基本就废掉了，只能开新 session。这个问题在未触发 ToolSearch 的新 session 中不会出现。

No files or tests are named. Start by reproducing the issue against https://api.kimi.com/coding/ with a fresh session, invoking ToolSearch and then sending a normal turn; compare the request context with a healthy session. Done means the resulting session no longer persistently returns HTTP 400 after MCP tool_reference messages are present.