Allow adding variant via prompttemplate files

[JonasHelming]

fixed #14507

What it does

Allows users to add custom variants to existing main prompts via adding .prompttemplate files.
If the file name of a .prompttemplate file starts with the id of an existing main prompt, the custom prompt file is treated as a variant.

How to test

• Create a new .prompttemplate file which starts with the id of an existing main prompt template.
• Browse to the respective agent and select the variant
• Edit the variant
• No other prompt feature should be influenced

Follow-ups

we might allow users to create variants in the UI

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[sdirix]

Works for me!

I tested editing the workspace agent template. Creating a new template and setting it in the AI configuration works fine.

There are some glitches when deleting this file:

• Create this custom variant template
• Set it in the UI for an agent
• Send a request for the agent, observe it is correctly set as system prompt

If the file is now deleted, the following happens:

• It's still shown in the AI configuration UI until the selection is switched back and forth
• Although it's gone, clicking on "Edit" will still open an editor for the no longer existing file
• When sending a request to the agent, it will use NO system prompt

What is likely going on is that, although deleted, Theia AI still tries to use the deleted prompt variant. In the UI this leads to the variant no longer appearing in the dropdown, but still being selected. At request time, the prompt can't be found and then no prompt is used.

This use case should be handled cleaner:

• The UI should be updated immediately
• The Edit button should always open the correct file
• Requests should fallback to their regular prompt

[JonasHelming]

Great catch, thank you!

New commit should fix the describe issue:

• We update the selection box on file changes
• We show to the user if a variant is no longer existing and disallow editing it
• If a variant is not available, but configured, an empty system prompt is expected, though

[sdirix]

There is one more problematic flow:

• When there are multiple variants, the flow works as expected.
• However when there is no variant left, then the UI disables all buttons, the dropdown vanishes, there is no error message and the user can't recover from the state without re-adding a variant

Steps to reproduce:

• Open AI configuration view
• Select workspace agent
• Click "edit", edit the template and use "File > Save As" to save it as a variant
• Select the newly added variant in the UI
• Delete the prompt template again
• Now the UI is in the broken state and does not recover without reloading or readding a variant

One more thing (could be a followup):

• Deleting the variant can also be accomplished via the "Reset" button.
• For these custom variants it would be nice if the button would show "Delete" instead as they are then gone in contrast to the "built-in" variants

Besides this edge case it seems to work great now 👍

[JonasHelming]

Great catch, fixed the describe workflow!
I will create a follow up for "delete".

[sdirix]

Works great for me. Thanks!