- drop the synthetic "search failed with exit code N" line (an rtk addition)
- surface the engine stderr verbatim in every path, incl. partial match + error
- remove the now-vestigial is_grep_error_exit (the "0 matches" it guarded is gone)
- error/exit matrix tests vs real grep/rg (#2465: an error is never a silent no-match)
Adrien Eppling