0629 — "schema" names a Postgres schema and nothing else

Context. Found while planning [0630], not planned work. The word already carried two senses — a payload’s version (SchemaVersion, message_log.schema_version, [0618]) and a migration target (vulkan migrate’s rows, pkg/migrate’s prose, ~25 comments calling the shared tables “the control-plane schema”) — and [0630] adds a third, the Postgres namespace. Postgres owns that word, and ## Vocabulary bans coining an alternative for a mechanism’s own noun, so the migration sense is the one that moves. The CLI was already inconsistent with itself about it: migrate up/down emitted {"scope": ...} while migrate status emitted {"schemas": [{"schema": ...}]} for the identical concept.

Decision. No rename — remove the need for a collective noun. migrate status --output json reports system as an object beside a topics array, and the text output prints one system: line above a TOPIC table. The result documents drop scope and schema entirely: the command already names what it targeted, so the document reports only what happened (topic present when one topic was named, absent otherwise). VK0017’s problem line becomes “system not registered”. The ~25 “control-plane schema” sites read “the control-plane tables”. Two ## Vocabulary rows record it, and schema joins the ### Attributes registry as the Postgres namespace.

Consequences. This fixes a real ambiguity, not just a word: only the __system. PREFIX is reserved, so a topic named exactly system registers, and migrate status printed two indistinguishable rows for it in both output modes. Splitting the list by what the rows are makes it unambiguous by construction, and the system needs no name because a database holds exactly one — the singleton [0625] settled and [0630] makes permanent. --output json is a contract [0575][0576]; pre-v1, so the break is taken, and nothing in the labs, the site, or tools consumed the old keys. Rejected: common.Owner/owner_kind as the collective noun — it is the library’s right name for a polymorphic row’s owner but reads backwards at a surface where nothing is being owned. Deferred: “schema version” for a MIGRATION version (VK0022/VK0023’s problem lines, ErrSchemaOlderThanBuild/ErrSchemaNewerThanBuild, ~8 files). The rule if it is taken up: migration_log.migration_version reads “migration version” and message_log.schema_version keeps “schema version”, so guides/schema-versions.mdx never moves.