Minimal text-diff test: preserve the invisible character

To reproduce an unexpected diff, reduce both texts to the shortest safe pair that still differs. Keep the exact newline, tab, non-breaking space, combining accent, or case distinction involved. Show the strings in a code block or escaped form so readers can see what the renderer hides. State whether the comparison should be byte-exact or normalized. A normal-looking word may not be the same sequence of Unicode code points.