Typing over a selection composed two edits in Lua —
delete_region() + insert_char() — so it recorded two undo steps:
one undo left the half-replaced text, two restored the original.
Undo granularity is per apply_edit in both modes (v0.1 pushes one
UndoEntry per edit; CRDT commits per edit via export and groups by
commit, with record_checkpoint unused), so the fix is to make
type-over one edit.
New core EditorCore::insert_char_over_region emits a single
EditOp::Replace when a region is active (cursor past the inserted
bytes, selection cleared) and delegates to insert_char otherwise.
The three type-over commands (buffer.newline / tab / self-insert)
call it via a new Lua binding instead of the delete+insert pair.
delete_region and insert_char are unchanged for their other
callers; region-aware backspace/delete already emit one op.
Verified one undo unit in BOTH modes (dual_mode
replace_is_a_single_undo_step covers v01 + crdt — a CRDT Replace is
delete-then-insert internally but one commit) plus an end-to-end
acceptance test through the key-dispatch path.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Levi Neuwirth
db073cc668