Two "parity" write paths drift silently when a shared step is copy-pasted instead of deduped

When two code paths are meant to produce identical writes — e.g. a legacy prose-extraction pipeline and a newer structured-ingest API both writing nodes to a graph store — keeping the "shared" logic as parallel copies causes silent divergence that no path's own tests catch.

Concrete instance: a soft-write confidence-dampening step. One path (prose extraction) wrote three node properties (extractionConfidence, softWriteAlpha, softWriteReason) via an inline Cypher SET; the other (the /v2/ingest API door) called a helper that, after a refactor/rename, set only extractionConfidence. Result: a soft-written node created via the API was byte-different from one created via the prose path — missing two annotations. Both paths passed their own unit tests; the divergence was invisible because nothing compared the two outputs.