DIFF_PLUS_RE matched both '+' and '-' (unified-diff markers), but '-'
is also a valid Markdown/YAML list prefix. When all replacement lines
start with '- ', the 50%-threshold heuristic in stripNewLinePrefixes
fires and strips every leading '-', corrupting list-item content.
Narrow the regex to match only '+' (added-line markers), which is the
stated intent of the docstring and the safe strip target. Removed
lines ('-') are never valid replacement content in any case.
Reproducer: passing content=["- [x] item"] as a bare string to a
set/replace op — the '-' is silently dropped, writing ' [x] item'.
Passing content as string[] bypasses stripNewLinePrefixes entirely and
was the workaround, but the root cause should be fixed.
Miroslav Drbal
8231ec3a7d