Persona JSON is loaded by some skills and not others. Topic-cluster context lives inside cluster vaults. Competitor positioning lives nowhere. Without a canonical source, each blog command re-derives "what is the brand" from whatever scraps of context it happens to have.
BRAND.md and VOICE.md fix that. They are the editorial equivalent of a persistent PRODUCT.md or DESIGN.md: one canonical source, written to the project root and loaded by the blog orchestrator at the start of every command. Run it once and every sub-skill, from write to audit, works from the same brief.