Split view shows even with no edits #1082

I was using Whiteboard to scope a feature in a codebase, and it kept showing
all the snippets in split view, even when there were no changes at all.

This doesn’t happen when the diff style is set to Unified. However:

• I prefer Split when there are actual changes, and I believe it’s the default.
• When both documents are identical, the second pane duplicates the content
  and reduces the space available to read it.
• A tour can mix unchanged context with changed code, so switching the entire
  review to Unified isn’t always ideal.

Could Whiteboard automatically show a single pane when the full base and head
documents are identical, while retaining the selected diff style when they differ?

The existing comparison already reports whether the documents are identical,
so that result could be used to choose the layout automatically.

I’ve opened #1081 with a proposed fix: document snippets automatically use a
single pane when the full base and head documents are identical.

This intentionally checks whole-document equality. An unchanged lens within
an edited file will still use the selected diff style, so it remains split
if Split is selected. Collapsing those unchanged ranges could be a follow-up.