Diff Bugs We Fixed

The bugs found in the diff view, what caused each, and why we fixed it the way we did. The user side is in Diffs.

Collapse unchanged folded nothing side by side.

• The issue: with Collapse unchanged on, the side by side diff showed every line; the inline diff folded fine.
• Why it happened: @codemirror/merge creates both editors' states first and adds its chunk field afterwards with StateEffect.appendConfig. Our fold field worked its folds out when it was created, when getChunks still returned nothing, and nothing filled it later.
• The fix and why we chose it: the field builds its folds in the transaction where the chunks first appear. That keeps splitFolds a plain extension given to the MergeView, instead of reconfiguring both editors after they exist. foldField.test.ts builds a real MergeView and checks both sides fold the same runs.

The inline diff had no scrollbar.

• The issue: scrolling the inline diff in the Changes view showed no vertical scrollbar.
• Why it happened: the change overview (the ruler at the right) sits over the body, and the editor was meant to stop short of it with right. CodeMirror's base theme forces position: relative !important on every editor, and a relatively placed box ignores right, so the editor ran under the ruler and the ruler covered its scrollbar.
• The fix and why we chose it: DiffFrame places the inline editor with position: absolute !important, so inset: 0 and the ruler's right both apply. We found it with inspect_elements in the real window: the editor reached under the ruler. Sizing the editor by hand (height and margin) would also work, but would copy what inset already says.