F2: findChangedRange only normalized the repeated-content INSERTION case
(oldTo<start), leaving the symmetric DELETION case (newTo<start) to return a
degenerate DocChange (newTo<from). Push BOTH ends forward by start-min(oldTo,newTo)
so the range stays non-degenerate (from<=oldTo, from<=newTo), matching ProseMirror's
diff bounds. The insertion case is byte-identical to before (min=oldTo → oldTo→start,
newTo→newTo+delta); the deletion/both-below cases are fixed. Never spuriously arms
the guard (arming needs oldTo>from AND newTo>from; normalization leaves exactly one
end ==from).
F1: add custom-typography.test.ts (15 tests) via the real Editor path (mirrors
intentional-clear.test.ts): findChangedRange normalization (insertion + the fixed
deletion), mapRangeThroughChange release/boundary/shift, and arming (local
undo-replace arms; remote y-sync change-origin does NOT; ordinary edit does NOT).
Adds test-only exports (undoGuardKey, findChangedRange, mapRangeThroughChange).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
agent_coder
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