fix: native tool type mapping for freeform apply_patch and web_search

[OnlyTerp]

Summary

This PR fixes three critical issues that break native tool compatibility when Codex Desktop routes through custom BYOK models via the shim:

1. apply_patch silently fails: Codex Desktop expects custom_tool_call for freeform apply_patch tools, but the shim emitted function_call with a generic schema. The Desktop rejected it because operation={"input":"..."} doesn't match the create_file/update_file/delete_file enum shape.

2. web_search stalls: Codex Desktop does not execute web_search for BYOK models — it expects the shim to return results. The shim was emitting function_call for web search and never executing the search, causing the model to loop forever waiting for results that never came.

3. custom_tool_call not emitted for any freeform tool: The streaming ResponsesStreamState always emitted type: "function_call" regardless of the original tool type.

What changed

codex_shim/server.py

• Added _build_tool_types(): Builds a map sanitized_tool_name -> original_tool_type from the request tools array before translation. This preserves the original type information that gets lost when we convert native tools to chat-completions function tools.

• Updated ResponsesStreamState.__init__: Accepts an optional tool_types dict.

• Updated ResponsesStreamState._open_tool: Looks up the original tool type and emits:

  • custom_tool_call for apply_patch (freeform)
  • web_search_call for web_search tools
  • function_call for everything else (backward compatible)

• Updated ResponsesStreamState._tool_item: Uses state["output_type"] instead of hardcoded "function_call".

• Updated all streaming paths: _stream_openai_chat, _stream_anthropic, and the Cursor passthrough all pass the tool type map when instantiating ResponsesStreamState.

• Added _perform_web_search(): Server-side DuckDuckGo search for the non-streaming path. Codex Desktop expects the shim to return search results; it does not execute them for BYOK models.

• Added _maybe_intercept_web_search(): Non-streaming interceptor that detects web_search_call items in the final response, executes the search, and replaces the call with a function_call_output containing the results.

codex_shim/translate.py

• Updated chat_completion_to_response: Accepts optional tool_types dict. Maps apply_patch -> custom_tool_call and web_search -> web_search_call in the non-streaming output array.

• Updated anthropic_to_response: Passes tool_types through to chat_completion_to_response.

tests/test_native_tool_types.py

New test suite covering:

• _build_tool_types for native and MCP tools
• custom_tool_call emission for apply_patch
• web_search_call emission for web_search
• Backward compatibility (no tool_types -> function_call)
• Anthropic path tool type mapping

Test plan

• python3 -m py_compile passes for all modified files
• New unit tests compile and pass (pytest tests/test_native_tool_types.py)
• Verified on live Codex Desktop 26.602 with kimi k2.7, grok, and Claude Fable 5
• apply_patch tool now succeeds with custom_tool_call output items
• web_search now returns results via server-side DDG execution
• function_call still works for all other tools (shell, MCP, etc.)

Fixes

• Fixes apply_patch silently failing on freeform models
• Fixes web_search stalling because results were never returned
• Fixes custom_tool_call not being emitted for any native tool

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>