Verified against plan9port: regexp(7) defines ^ as 'beginning of a line'
and $ as 'end of a line', and sam's regexp.c BOL (p==0 || prev=='\\n') /
EOL (next char '\\n') confirm per-line anchoring. The engine was matching
with buffer-wide anchors, so ,s/^/> /g only touched the first line and the
sam idiom ,x/.+/ s/^/> / failed to prefix each line.
Fix: compile every pattern with QRegularExpression::MultilineOption. '.'
still does not cross newlines (sam-faithful; PCRE default). Add 3 regression
tests (caretIsPerLine, dollarIsPerLine, samAnchorIdiom); 30/30 engine tests.
Docs: correct docs/SAM.md — ^/$ per-line is faithful, not a deviation;
reframe PCRE extras as an escape hatch (prefer structural composition), not
'free upgrades'. Fix the panel hint and PLAN.md accordingly.
4cdd762bb6