Codex Responses proxy drops tool_search during request normalization

[TerenceXin]

Summary

When 9Router is used as a Codex Responses API proxy, tool_search is removed from the outgoing request before the request is forwarded upstream.

This breaks Codex deferred tool discovery. In Codex Desktop, tools such as app automation, thread-management tools, and multi_agent_v1 tools are normally discovered through tool_search. Once the proxy drops tool_search, the model has no entrypoint to discover those deferred tools, so they appear to be missing in the session.

This is a request-normalization issue in 9Router, not a model capability issue.

Affected code

open-sse/executors/codex.js

normalizeCodexTools(body) currently keeps:

• function
• namespace
• tool types listed in CODEX_HOSTED_TOOL_TYPES

But tool_search is neither a function nor in CODEX_HOSTED_TOOL_TYPES, so it is filtered out.

Minimal reproduction

Run this from the 9Router source checkout:

node --input-type=module <<'EOF'
import { CodexExecutor } from './open-sse/executors/codex.js';

const executor = new CodexExecutor();
const body = {
  model: 'gpt-5.5',
  input: [
    { type: 'message', role: 'user', content: [{ type: 'input_text', text: 'probe' }] }
  ],
  tools: [
    { type: 'tool_search', execution: 'sync', description: 'Discover deferred tools', parameters: { type: 'object', properties: {} } },
    { type: 'namespace', name: 'codex_app', description: 'app tools', tools: [
      { type: 'function', name: 'automation_update', description: 'automation', parameters: { type: 'object', properties: {} }, defer_loading: true }
    ] },
    { type: 'function', name: 'plain_fn', description: 'plain', parameters: { type: 'object', properties: {} } }
  ],
  stream: true
};

const before = body.tools.map(t => t.type + ':' + (t.name || ''));
executor.transformRequest('gpt-5.5', body, true, { connectionId: 'probe', providerSpecificData: {} });
const after = body.tools.map(t => t.type + ':' + (t.name || ''));

console.log(JSON.stringify({ before, after, dropped: before.filter(x => !after.includes(x)) }, null, 2));
EOF

Actual output:

{
  "before": [
    "tool_search:",
    "namespace:codex_app",
    "function:plain_fn"
  ],
  "after": [
    "namespace:codex_app",
    "function:plain_fn"
  ],
  "dropped": [
    "tool_search:"
  ]
}

Expected behavior

9Router should preserve tool_search for Codex/OpenAI Responses requests when forwarding to a Codex-compatible upstream.

Impact

• Codex Desktop deferred tools cannot be discovered through tool_search.
• App automation tools, thread-management tools, and multi_agent_v1 tools appear missing when using 9Router as the provider.
• This can be mistaken for a Codex version/configuration problem, but the immediate cause is that the proxy removes the discovery tool from the request.

Additional observation

The same request-normalization path also drops custom / freeform tools, because custom is also not in the allowlist. For example:

{ type: 'custom', name: 'apply_patch', description: 'patch', format: { type: 'grammar', syntax: 'lark', definition: 'start: /.+/' } }

This may be related to #1371, but it is a different code path: this issue is about request-time filtering in open-sse/executors/codex.js, while #1371 describes response translation not preserving custom_tool_call output.

Related issues

• Codex subagent compatibility: multi_agent_v2 tool exposure and encrypted tool schema support / Codex 子代理兼容性问题 #1873 discusses broader Codex subagent compatibility and missing subagent tools.
• Codex subagent tools fail when multi_agent_v2 is enabled: spawn_agent.message uses encrypted parameters #1758 discusses multi_agent_v2 encrypted tool parameter rejection.
• Codex apply_patch broken via /v1/responses: custom_tool_call not preserved in translator #1371 discusses custom_tool_call / apply_patch response translation.

Suggested fix

Update normalizeCodexTools() to preserve tool_search for Codex Responses requests, and add regression coverage showing that these tool types survive request normalization:

• function
• namespace
• tool_search
• hosted tools such as web_search, image_generation, mcp, local_shell, code_interpreter, computer

If custom tools are intended to be supported, preserve them there as well, including their format payload.