Setting focus on Claude Code Extension always starts a new Claude Code panel/editor when there is a single editorViewColumn or when it's not the top/frontmost editor

[couimet]

While testing for #529 , I got to realize that Claude Code Extension starts new panels/editors when it doesn't already have one open in a top-most editor.

I decided to punt on this in the context of #529 to avoid feature creep and because an easy workaround is to always keep Claude Code Extension as a front-most/top-most editor in split view (multiple view columns).