Allow configuring default/minimum editor group width when a new group opens

[phillza]

Problem

When a new editor group opens (e.g. clicking a file in the Explorer), VS Code redistributes space equally across all groups (splitSizing: distribute) or splits the active group in half (splitSizing: split). There is no way to specify a maximum or default width for the newly-opened group, so it can end up unexpectedly wide and compress adjacent panels.

Use Case

A common modern layout has two or more persistent panels side-by-side (e.g. AI assistant panels like Claude Code) taking up most of the editor area, with a narrow column reserved for occasional file previews. Today, every time a file is opened from the Explorer it widens the file preview column back to its "fair share" of the space, compressing the AI panels.

The workaround is:

1. Lock the AI assistant editor groups so files can't open there
2. Pre-size the file preview column manually each session

This works but the sizing doesn't persist reliably across restarts.

Requested Feature

Add a setting such as:

// Maximum width (in px) that a newly-opened editor group will claim
"workbench.editor.newGroupMaxWidth": 300

Or alternatively a per-group "fixed width" mode similar to how terminal panel size can be locked.

Prior Art

• Issue Allow to configure the minimal width of an editor #54470 was closed during issue grooming despite 100+ votes and strong community interest
• Related: workbench.editor.splitSizing (auto | split | distribute) controls proportions but not absolute sizes

Expected Behaviour

When newGroupMaxWidth is set, a newly-created editor group opens at no wider than that value (or the available space if less), leaving adjacent groups undisturbed.

🤖 Submitted via Claude Code

[vs-code-engineering]

This feature request is now a candidate for our backlog. The community has 60 days to upvote the issue. If it receives 20 upvotes we will move it to our backlog. If not, we will close it. To learn more about how we handle feature requests, please see our documentation.

Happy Coding!