Only warn for duplicate module if metaKey is not specified

Editor assessment

The subject states the conditional behavior exactly — a duplicate module only warns when no metaKey is specified — so the header communicates the fix, its condition, and its beneficiary without the diff, and fix(core) classifies and locates it correctly. Hygiene is clean: imperative mood, no trailing period, sensible length, no ticket junk. No body is needed for a contained validation fix, and no footer is required. A line on the false duplicates users saw would add depth; the message is already clear, accurate, and publishable in the good band.