* fix(sandbox): honor single-bound line ranges in read_file
read_file only sliced content when BOTH start_line and end_line were
provided, so read_file(path, start_line=100) or read_file(path,
end_line=50) silently returned the whole file. Handle one-sided ranges:
default the missing bound (start->1, end->EOF), clamp start to 1, and
return clear messages when start_line exceeds the file length or start_line
> end_line.
* address review: guard one-sided end_line <= 0 in read_file
Add symmetric end_line guard and run the inverted-range check regardless
of which bounds are explicit, so a lone end_line<=0 returns a clean
error instead of a negative-index slice. Per @willem-bd review on #4078.
Co-Authored-By: Claude <noreply@anthropic.com>
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Co-authored-by: Claude <noreply@anthropic.com>
