A regex \n (or a raw newline) in a search_files content pattern cannot
match in rg's default line-oriented mode. It previously either
hard-errored ('the literal "\n" is not allowed in a regex' — 17
occurrences in the production window) or, after the newline-warning
patch, returned 0 matches with an explanation — either way the model's
cross-line search intent required a manual workaround.
The rg engine now detects the pattern shape (_pattern_has_regex_newline,
already used by the warning path: odd-backslash \n escape or raw
newline; escaped \\n literals excluded) and enables -U/--multiline up
front, noting the mode switch in the result warning. Plain patterns are
untouched; the old line-oriented explanation is retained for the grep
fallback engine, which has no multiline mode.
Teknium