Why: The registration gate classified Word packages from a hard-coded ZIP member path, allowing alternate main-part paths to bypass the gate and rejecting unrelated ZIP archives.
Evidence: Focused OPC registration tests; go test -count=1 ./internal/tools; go test -count=1 ./...; go test -race -count=1 ./internal/tools ./internal/runmgr; go vet ./...; go build ./...; git diff --check.
Impact: Resolve package-level officeDocument targets safely, classify all conventional Word main content types through OPC defaults or overrides, and fail closed on malformed, ambiguous, external, or traversing metadata while preserving non-Word artifacts.
Refs: Task 10; /tmp/task10-backend-final-closure-last.md