validate_workflow_source_paths folded case before applying NFC, but
case folding is not closed under canonical equivalence: a decomposed
sequence and its precomposed form can fold to different strings. Two
supplied paths that a normalization-insensitive filesystem treats as
one entry therefore passed the collision check, and staging silently
overwrote one file with the other.
Apply NFC first, then fold, then normalize again, and add the Greek
pair that reproduced the gap.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>