[Bug] Mid-Conversation switch references latest selected agent instead of the last agent used for code generation

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

26.903.61454

What subscription do you have?

Plus

What platform is your computer?

Windows

What issue are you seeing?

The "degraded performance" warning dialog tracks model state against the latest selected LLM in the picker rather than the last LLM that actually executed a generation. When switching from LLM A (which just generated code) to LLM B, the warning dialog appears. When the user immediately switches back to LLM A to avoid the issue, the dialog triggers again warning that switching back will cause degraded performance—even though LLM A is the model that just generated the previous response.

Impact

• Misleading UI warnings that confuse the user.
• Forces unnecessary warning prompts when attempting to undo an accidental or unexecuted model selection.

What steps can reproduce the bug?

1. Generate an output using LLM A.
2. Select LLM B in the model picker mid-thread.
3. Observe the warning dialog indicating that switching to LLM B may degrade performance.
4. Without generating any output with LLM B, select LLM A again to return to the active context.

• The degraded performance warning dialog appears again when switching back to LLM A.
• The warning logic compares against the latest chosen model in the picker (LLM B) rather than verifying which model actually ran the last generation cycle.

What is the expected behavior?

• Switching back to the model that produced the last generation (LLM A) should be recognized as returning to the active model state.
• The warning dialog should evaluate against the last LLM used for generation, suppressing false-positive warnings when the user reverts an uncommitted picker change.

Additional information

No response

Start at the model picker and the degraded performance warning dialog, then trace how the selected model and the last generation model are tracked during a conversation. Reproduce the A/B switch sequence described in the issue and verify that returning to A after no generation with B no longer shows the warning.