Keep caller-selected replacement text literal with a callback, preserving
empty-search positions instead of changing their split/join behavior.
Commit the replacement interpretation for captures using custom patterns so
legacy records cannot report this producer correction as a target change.
BREAKING CHANGE: Captures with custom normalization patterns use
literal-replacements-v1 and cannot be compared with legacy unversioned
pattern captures. Capture both sides with the same replacement semantics;
legacy captures remain readable and captures without patterns are unaffected.