API error 400 Request contains an invalid argument.

### What happened?

[ACTION REQUIRED] 📎 PLEASE ATTACH THE EXPORTED CHAT HISTORY JSON FILE TO THIS ISSUE IF YOU FEEL COMFORTABLE SHARING IT

### What did you expect to happen?

It started to happen often that i have this message at the end of an AI's response:
[API Error: [{
"error": {
"code": 400,
"message": "Request contains an invalid argument.",
"errors": [
{
"message": "Request contains an invalid argument.",
"domain": "global",
"reason": "badRequest"
}
],
"status": "INVALID_ARGUMENT"
}
}
]]

After the first error message the AI answer with this error at every request, i have to close the session and resume it.

### Client information

* **CLI Version:** 0.58.0
* **Git Commit:** ac9431c9e
* **Session ID:** 05d99561-7ff8-4452-82b3-755e1419d99c
* **Operating System:** darwin v23.6.0
* **Sandbox Environment:** no sandbox
* **Model Version:** auto-gemini-2.5
* **Auth Type:** oauth-personal
* **Memory Usage:** 202.0 MB
* **Terminal Name:** Unknown
* **Terminal Background:** #191a1c
* **Kitty Keyboard Protocol:** Unsupported
* **IDE Client:** PhpStorm 2026.2.2

### Login information

_No response_

### Anything else we need to know?

_No response_

Start by reproducing the repeated 400 INVALID_ARGUMENT response in gemini-cli 0.58.0 with the reported auto-gemini-2.5 model and OAuth authentication. The issue does not identify a file, test, request argument, or reliable reproduction steps, so first inspect the CLI's API request and session-resume paths. Done means identifying the invalid request or state transition and preventing the error from recurring on every request.

Written by the indexing model from the issue text.