Bug: MCP tools with top-level oneOf inputSchema receive empty args ({}), rejected by local validation (CLI 0.40.1)

Bug Report: kimi-cu-win MCP tools with top-level oneOf schema receive empty args ({}) — client-side validation rejects all calls

Summary

When calling kimi-cu-win MCP tools whose inputSchema uses a top-level oneOf (e.g. get_app_state, activate_window, click, scroll, drag), the arguments emitted by the model are dropped before reaching the MCP server: the session wire log records "args":{}, and the call fails local validation with:

Invalid args for tool "mcp__kimi-cu__get_app_state": must have required property 'pid';
must have required property 'app'; must have required property 'window_id';
must match exactly one schema in oneOf

Tools whose schema has top-level required fields (e.g. type_text with snapshot_id/text) pass arguments through correctly and reach the MCP runtime, so the issue is specific to schemas where required exists only inside oneOf branches.

Environment

• Kimi Code CLI: 0.40.1 (standalone install at ~/.kimi-code/bin/kimi, Windows)
• OS: Windows 11 (10.0.26200)
• Plugin: kimi-cu-win 0.2.17; runtime kimi-cu.exe 0.2.17 (doctor all green, agent running)

Evidence

1. Wire log (wire.jsonl) shows the model's tool calls arrive at the harness with empty args:

   "mcp__kimi-cu__get_app_state","args":{},"time":1788920322774
   "mcp__kimi-cu__get_app_state","args":{},"time":1788920333296
   ...
   "mcp__kimi-cu__type_text","args":{"snapshot_id":"diag-probe","text":"probe"},"time":1788921554319
   

   • get_app_state / activate_window: every attempt (8+) recorded args:{} → rejected by local schema validation, never reached the MCP server.
   • type_text (top-level required: ["snapshot_id","text"]): args passed through, reached the runtime, and got a real runtime error (type_text requires a target window...), proving the transport works.

2. Runtime is healthy and the same call works when sent directly: piping JSON-RPC over stdio into kimi-cu.exe mcp:

   {"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"get_app_state","arguments":{"window_id":65948,"mode":"text","max_chars":500}}}
   

   returns a full, valid get_app_state result. So the runtime, plugin manifest, and MCP server are all fine — arguments are lost in the CLI harness layer.

Affected tools

All kimi-cu-win tools with top-level oneOf and no top-level required: get_app_state, activate_window, click, scroll, select_text, drag (and possibly MCP tools from other servers with the same schema shape).

Steps to reproduce

1. Install kimi-cu-win plugin 0.2.17 + runtime 0.2.17 on Windows, CLI 0.40.1.
2. In a session, call mcp__kimi-cu__get_app_state with {"window_id": <any valid HWND>}.
3. Observe Invalid args ... must match exactly one schema in oneOf, and "args":{} in wire.jsonl.

Suspected cause

The CLI's MCP tool-schema handling (validation and/or the schema presented to the model) mishandles top-level oneOf when required is declared only inside branches — arguments not matching a flattened property set are stripped, so the validator then sees {} and reports every branch's required as missing.

Attachments

• Debug ZIP exported via kimi export (contains wire.jsonl with the evidence above).

Start by tracing the CLI's MCP tool-schema handling, especially the validation or model-schema path for tools using a top-level oneOf. Reproduce with get_app_state and compare its empty args with type_text's preserved arguments; done means branch arguments reach validation and the MCP server without breaking existing top-level required schemas.