Resuming a session has strange ux with regards to model and reasoning
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Description
Describe the bug
If you have a session that's was done on gpt-5.6-terra with medium, and you --resume it, with either --model=gpt-5.6-luna --reasoning-effort=xhigh or gpt-5.6-luna + xhigh in your ~/.copilot/settings.json, the reasoningEffort is honoured, but the model is not, and your resumed session will be on gpt-5.6-terra xhigh
Feels like this should be consistent? It should either:
- Explicitly honour the original session, keeping the settings the same
- Explicitly honour your copilot CLI args and/or settings.json
I would rather the latter personally, but raising this as a UX bug.
This also affects sessions resumed via copilot-sdk.
Affected version
1.0.77
Steps to reproduce the behavior
No response
Expected behavior
No response
Additional context
No response
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start at the --resume flow and trace how --model, --reasoning-effort, and ~/.copilot/settings.json are applied when restoring a session. Check the corresponding copilot-sdk resume path as well. Done means the chosen precedence is consistent for both CLI and SDK sessions, with regression coverage for model and reasoning effort.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- shell
- Domain
- ai, cli
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 52/100