## Problem
Toggling large diffs via fugitive's `=` caused the top of the buffer to
re-render and glitch. `ensure_cache` always created a new cache entry
with
`pending_clear=true` and `highlighted={}`, forcing `on_win` to clear and
re-highlight every visible hunk — including stable ones above the toggle
point that never changed.
## Solution
On reparse, compare old and new hunk lists using a prefix + suffix
matching
strategy. Hunks that match (same filename, line count, and sampled
content)
carry forward their `highlighted` state so `on_win` skips them.
Comparison
is O(1) per hunk. Only runs when the old entry had
`pending_clear=false`;
`invalidate_cache`/`ColorScheme` paths still force full re-highlight.
Closes#131
6040c054cb