Bug: BadRequestError after Computer Use failure breaks entire session

Steps to Reproduce

1. Start a new Codex Desktop session (version 0.140.0-alpha.19)
2. Ask the agent to use the Computer Use plugin
3. The Computer Use plugin fails due to a permissions issue
4. Agent switches to in-app browser and tries to continue
5. After this point, every subsequent user message triggers a BadRequestError:

BadRequestError: OpenAIException - {"error":{"message":"Expecting property name enclosed in double quotes: line 1 column 2 (char 1)","type":"BadRequestError","param":null,"code":"400"}}

1. The entire session is broken and must be abandoned - no user message can be processed

Expected Behavior

• The session should recover gracefully after a plugin failure
• Subsequent user messages should be handled normally

Actual Behavior

• After the Computer Use failure, all subsequent requests return a 400 BadRequestError
• The error message suggests malformed JSON being sent to the OpenAI API
• This is not a permissions issue (which would be 403/401) - it is a JSON serialization bug

Root Cause Hypothesis

• The agent serialization of conversation context into JSON payload appears to be corrupted after the Computer Use failure
• The line 1 column 2 error indicates the entire request body structure is broken from the start
• Possible cause: JSON.stringify is not being used to serialize messages

Environment

• Codex Desktop version: 0.140.0-alpha.19
• Model: agnes-2.0-flash
• OS: Windows