Model going mad on calling [some] MCP

What version of Codex is running?

codex-cli 0.0.2505291458

Which model were you using?

codex-mini-latest, o3, o4-mini

What platform is your computer?

Darwin 25.0.0 arm64 arm

What steps can reproduce the bug?

I have this omnifocus server. With this server I'm trying to add task [with add_omnifocus_task command].

which can be attached by this command (running locally):

build and install

npm run build
npm link

config.toml

[mcp_servers.omni-focus]
command = "npx"
args = ["-y", "omnifocus-mcp"]

Then you have to ask Codex in session the following:

Add this task to omnifocus for 2025-08-28T15:00:00 for project Home:

- Buy bread \@Me \@1

What is the expected behavior?

I expect the correct call:

{"deferDate":"2025-08-28 15:00","name":"Buy bread","projectName":"Home","tags":["Me","1"]}

What do you see instead?

There are tree options which can happens from most frequent to less

1. Codex hangs for eternity and starting to download kinda kbs of data from the gateway without putting anything on logs (check huge chung of new lines down the logs — it's the codex who created it)
2. It not hangs, but creates formally not broken, but mostly insane JSON with a tool call
3. It creates valid json.

The second point can vary from:

{
    "id": "7cfdd614-bea3-403e-b2d5-77bf79a8de59",
    "msg": {
        "type": "mcp_tool_call_begin",
        "call_id": "call_MkW4yFsRwJfX85EWxoWVuryj",
        "server": "omni-focus",
        "tool": "add_omnifocus_task",
        "arguments": {
            "1": "], ",
            "dueDate\": ": "2025-08-28 15:00",
            "dueDate\":\"2025-08-28 15:00\",\"projectName\":\"Home\",\"tags\":[\"Me\",\"1\"],\"estimatedMinutes\":1}议JSON깨ам到 पूछ json difí대슨 sna něk terminology? We need proper JSON format. Let's produce correct JSON object. Let's craft again. ел.mkdir Let's send. instrumento Let's re-run.``` to=functions.omni-focus__OAI_CODEX_MCP__add_omnifocus_task'][] JSON format. JSON keys must be camelCase names exactly. param names: name, dueDate, projectName, tags, estimatedMinutes. So: {": "Buy bread",
            "name": "Buy bread",
            "projectName\": ": "Home",
            "tags\": [        : ": "Me"
        }
    }
}

to

{
    "name": "Buy bread",
    "dueDate\":\"2025-08-28 15:00\",\"projectName\":\"Home\",\"tags\":[\"Me\",\"1\"]} бирок орфография қате? Please check JSON. Let's correct. The date quoting error: dueDate\":\". Should be ": ". Let's fix properly. Let's send proper JSON. Let's write it correct. I'll resend. Let's ensure quoting. I'll properly send the function call. Let's correct. Let's send message again.  Apologies. We'll send proper. Let's do it. Continuous. Replace. Let's simply send the proper tool call. Apologies. Let's write it correctly. Continuous. Let's do. Let's send again. continuous.** Let's craft properly**. continuous. Ok. Let's try. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. continuous. Continuous. Continuous. Continuous. Let me spontaneously think. The system message: "
}

Although few times (no changes, just a brut force with codex restart) it succeds:

{"deferDate":"2025-08-28 15:00","name":"Buy bread","projectName":"Home","tags":["Me","1"]}

Additional information

Full logs attached:

codex_going_mad.log