Codex App sends tool_search_call.arguments as a JSON string, causing Responses API invalid_type errors

What version of the Codex App are you using (From “About Codex” dialog)?

Codex App: 26.623.19656.0 (please confirm from About Codex) Codex CLI: 0.142.5

What subscription do you have?

team

What platform is your computer?

_No response_

What issue are you seeing?

Codex App intermittently records/replays internal tool_search_call.arguments as a JSON-encoded string instead of a JSON object. The next Responses API request fails before the assistant can continue.

Observed errors:

Invalid type for 'input[28].arguments': expected an object, but got a string instead.
Invalid type for 'input[62].arguments': expected an object, but got a string instead.

This does not appear to be a chrome-devtools MCP server failure. The chrome-devtools MCP tool list is available:

listed MCP server tools while building tool list server_name=chrome-devtools tool_count=29

But internal tool_search_call items are sometimes malformed.

Examples from local rollout JSONL, with PII redacted:

1. Session:

019f3f79-5b48-7de1-9f57-0e4179b70a18

Bad input[28]:

{
"type": "tool_search_call",
"call_id": "call_H91Re6731TtEVu1BXFJJ2cuf",
"status": "completed",
"execution": "client",
"arguments": "{\"query\":\"chrome devtools network request list get current page navigate click input\",\"limit\":10}"
}

Expected:

{
"type": "tool_search_call",
"call_id": "call_H91Re6731TtEVu1BXFJJ2cuf",
"status": "completed",
"execution": "client",
"arguments": {
"query": "chrome devtools network request list get current page navigate click input",
"limit": 10
}
}

1. Same session later:

Bad input[62]:

{
"type": "tool_search_call",
"call_id": "call_Q5wet5GUYIcEiweMrZO8jJjO",
"status": "completed",
"execution": "client",
"arguments": "{\"limit\":10,\"query\":\"spawn agent wait agent subagent multi agent\"}"
}

The local router also logged:

failed to parse tool_search arguments: invalid type: string "...", expected struct SearchToolCallParams

What steps can reproduce the bug?

1. Start a Codex App thread on Windows.
2. Use a task that requires Chrome DevTools MCP or asks the model to check available tools.
3. Example prompt pattern:

• "Use Chrome DevTools MCP to inspect real page network requests."
• "Check whether multi-agent/subagent tools are available."

1. The assistant emits a message such as:

"Chrome DevTools MCP is available... checking whether multi-agent tools are available."

1. Codex emits an internal tool_search_call.
2. In some cases, tool_search_call.arguments is stored/sent as a JSON string rather than an object.
3. The next Responses API request fails with:

Invalid type for 'input[n].arguments': expected an object, but got a string instead.

What is the expected behavior?

tool_search_call.arguments should always be serialized as a JSON object before storing/replaying/sending to Responses API. A malformed internal tool_search item should not poison the thread history.

Additional information

• This reproduced across multiple sessions:
• 019f3d04-f96e-76c0-abf4-a04c5b9394cf
• 019f3f79-5b48-7de1-9f57-0e4179b70a18
• It can happen without auto-compaction.
• Auto-compaction may make the issue more visible because malformed history is replayed.
• Workaround: manually repair the rollout JSONL by converting stringified tool_search_call.arguments to objects and removing orphan parse-failure outputs, or avoid triggering tool_search.