Freeze when opening coding agent session

[mjbvz]

1. Open a coding agent session that's somewhat long

Bug
Editor freezes for a half second. Profile shows that there is a hang as we render all the chat content

Profile: Trace-20250826T163013.json.zip

[mjbvz]

Lots of these are calls to codeBlockRendeerSync. I think we end up creating a ton of extra editors as part of this, but then only show a handful at the end

@rebornix I think you know more about tree/list rendering. I think the main problem here is that when we open the session we scroll to the end, which forces all of the content to be rendered so we can figure out heights. Are there any tricks from notebooks we can use to optimize this?

[mjbvz]

Oh actually I misunderstood what is happening. The content is all rendered all at once because the entire log is put into one big response. Definitely need to try fixing that

[mjbvz]

@roblourens This sounds like it could be a lot of work but I think one way to improve long response rendering would be to use the tree API so that the response parts are rendered as children of the response node. That way long responses with a bunch of tool calls could be rendered incrementally instead of all in one shot

Is that something we've considered before?

[roblourens]

Good investigation. Yeah, I've thought about that as I see agent trajectories getting longer, and I think that what you suggest is probably the way to go. Will be a big refactoring of the list renderer but it will probably be simpler in the end.

In some cases it might make the arrow navigation annoying. But in other cases it might help solve some problems. Keyboard navigation of the chat list has always been a bit awkward.

[roblourens]

This could be a fun debt week task for me or Justin but I would trust you to do it too if you want to work on it.