PositroNB: Restart kernel button

[seeM]

Add the Restart Kernel button to Positron notebooks, addresses #9789.

Screen.Recording.2025-10-10.at.19.02.37.mov

Release Notes

New Features

• N/A

Bug Fixes

• N/A

QA Notes

@:notebooks

[github-actions]

E2E Tests 🚀
This PR will run tests tagged with: @:critical @:notebooks

^{readme  valid tags}

[rodrigosf672]

@seeM Based on your changes, what do you expect to happen in the scenarios 2-4?

Cases

1. User attempts to restart the kernel of a saved notebook while nothing is running (most trivial).
2. User attempts to restart the kernel of an unsaved notebook while nothing is running (trivial);
3. User attempts to restart the kernel of a saved notebook while something is running (complex);
4. User attempts to restart the kernel of an unsaved notebook while something is running (most complex).

Outcomes

1. Kernel restarts with no additional prompts/dialogs.
2. ?
3. ?
4. ?

[cindyytong]

@seeM Awesome!

This is looking good however I am concerned that we are running out of space in the nav bar and not grouping related actions in the same area. I put 2 mockups for exploration here to determine next steps: https://www.figma.com/design/z9EOP4qLLzR08PNxe4M0Ei/Positron-Notebooks---Design-Audit?node-id=305-2&t=8CHFBPPjEQfYYkiB-1

[nstrayer]

Code itself looks great. I'll leave the design part to further discussions.

[seeM]

Thanks for the reviews! I've updated the UI based on your feedback:

1. Run All and Clear Outputs no longer show titles – they have tooltips to clarify any confusion
2. "+ Code" and "+ Markdown" moved to the left
3. Restart Kernel moved to the right and no title (to be moved into a submenu in Positron Notebooks: Enhanced kernel info in the notebook toolbar #9722)
4. Show Console moved to the More Actions submenu

[cindyytong]

@seeM looking great! Based on the design we made the other day with a new dropdown for the kernel, are you suggesting that whole dropdown gets handled in #9722

Where restart kernel and show console would be a submenu item in this dropdown?

My understanding was that 9722 would just capture putting the kernel info in the new dropdown

[midleman]

I don't see any particular e2e tests that exercise the notebook kernel restart. I can def add a test for that. However, I was curious if there are any particular checks I should assert? Is there any kind of persistence that is expected or is everything wiped?

[seeM]

@midleman in terms of state, it should behave exactly as restarting a console session. Some ideas:

• The button is disabled while the session is starting, and while shutting down after clicking
• Can execute a cell afterwards, execution order is reset and all state was wiped

[seeM]

@rodrigosf672 IIUC whether the notebook is saved or not shouldn't affect restart behavior.

Perhaps restarting while something is running should display a warning, and perhaps a warning should also be displayed based if data will be lost. Will start a discussion in Slack.