Desktop app: existing conversations do not pick up updated API credentials, causing stream disconnected errors

Describe the bug

When switching API providers or credentials (e.g., changing model_providers config with a new API key and base URL), existing desktop app conversations continue using the old credentials cached in their session. This causes stream disconnected before completion: stream closed before response.completed errors.

CLI sessions are unaffected because each new CLI session starts fresh with the current config.

To Reproduce

1. Configure ~/.codex/config.toml with a custom provider (e.g., Provider A) and start a conversation in the desktop app.
2. Update config.toml to point to a different provider or API key (e.g., Provider B).
3. Continue the existing conversation in the desktop app.
4. Observe: stream disconnected before completion

Expected behavior

The desktop app should either:

• Refresh credentials at the start of each turn, or
• Clearly indicate that the session is stale and suggest starting a new conversation

Workaround

Start a new conversation in the desktop app. New conversations correctly use the updated config.

Environment

• OS: Windows 11
• Codex Desktop App version: 26.616.32156
• CLI works correctly with the same config