- Backspace and delete-char remove a whole UTF-8 character (they
removed one byte, leaving an invalid lead byte in the file), and
record the full character for undo.
- Left/right step over whole characters; up/down snap the column to a
character boundary and clamp the row, which also removes an unsigned
underflow in move-down when the cursor was past the last row.
- Horizontal scroll offsets are computed in display cells, the way the
terminal renderer draws (tabs, wide characters), instead of bytes, so
long non-ASCII lines no longer scroll to blank with the cursor off
screen. The mouse column mapping uses the same measure.
Audit findings B5, B6.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015rcVQiiWyTzoNrsvLSaAfB
Claude
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