[farhantawfeeq56]

Motivation

Using gpt-6-luna (and likely other Responses-backed models) on a plan without Provider API access routes every request through the /alpha/generate fallback. After the model calls tool_search, every follow-up turn fails with:

400 Missing required parameter: 'input[N].arguments'.

The session cannot recover. I reproduced it with a minimal generate request:

History item	Result
assistant tool call named tool_search + its result	Missing required parameter: 'input[2].arguments'
identical call named bash	accepted
identical call named search_tools	accepted
tool_search call with deepseek/deepseek-v4.1-flash	accepted

So the backend special-cases a tool literally named tool_search when it rebuilds OpenAI Responses items and drops the required arguments. The provider sends valid tool-call input; the bug only affects the generate wire and Responses-backed models.

Summary

• Alias tool_search → search_tools in the /alpha/generate payload (tool declarations, replayed calls, and tool results) for models served by the OpenAI Responses wire.
• Map the model's search_tools call back to tool_search before emitting it to the host, so the call still runs the real tool.
• Gate the alias behind a new isResponsesModel core dependency wired from the registered model catalog. Chat Completions (DeepSeek) and Anthropic models are untouched.

Files changed

• src/core.ts
  • Added TOOL_SEARCH_* constants and wireToolName() / hostToolName() helpers.
  • Generate body now aliases tool names in messagesToCC() and toolsToJson().
  • Incoming stream events translate search_tools back to tool_search.
• src/converters.ts
  • toolsToJson() accepts an optional toolNameAlias.
  • messagesToCC() accepts toolNameAlias and applies it to tool calls and tool results. Default behavior is unchanged.
• src/types.ts
  • Added optional CoreDependencies.isResponsesModel.
• index.ts
  • Moved the modelApis map above createStreamCommandCode() and passed isResponsesModel, resolved from the catalog.
• tests/test-pure-functions.ts
  • Aliased and default (identity) coverage for toolsToJson() and messagesToCC().
• tests/test-stream.ts
  • Generate serialization test for a Responses model: request uses search_tools, response is mapped back to tool_search.
  • Non-Responses model test: names stay tool_search.
• CHANGELOG.md
  • Unreleased entry describing the fix.

Verification

• npm run typecheck passes.
• New unit and stream tests pass (tests/test-pure-functions.ts, tests/test-stream.ts; 118 tests).
• Resumed the exact failing session state with gpt-6-luna: previously 400 input[70].arguments, now completes normally.
• npm test passes except tests/test-release.mjs, which fails identically on a clean main checkout in this Windows environment (pre-existing CRLF/fixture issue, unrelated to this change).

After merge

• Sessions that previously failed right after a tool_search call recover on the next turn.
• No behavior change for DeepSeek, Anthropic, or Provider API users.
• The alias can be removed once the generate backend preserves arguments for calls named tool_search.