chore(changeset): record the ViewMetadata type narrowing

A minor, BREAKING-bannered changeset for @objectstack/spec: the published
type narrows while the runtime accept set does not move. Its ADR-0087
disposition is no-migration-prescription.

Claude-Session: https://claude.ai/code/session_013RDBh5DqXd2xnLwvHLgLFr
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

.changeset/view-metadata-type-not-unknown.md

@@ -0,0 +1,35 @@
+---
+'@objectstack/spec': minor
+---
+
+fix(spec): the published type `ViewMetadata` names a `view` body instead of being `unknown` (#19871)
+
+Clause-②: no (narrowing)
+
+**BREAKING for TypeScript code that annotates with `ViewMetadata`**: a narrowing of a published
+TYPE, landing in the launch window as `minor` (the lockstep convention: the bump level is not the
+carrier, this banner and the disposition below are). The runtime accept set does not move at all:
+`ViewMetadataSchema` is unchanged, and a 44-body parse probe answers byte-identically before and
+after.
+
+`ViewMetadata` was declared as `z.input<typeof ViewMetadataSchema>`. That schema is a
+`z.preprocess`, whose input type is `unknown`, so the name documented as "any persisted view
+metadata body: container | ViewItem record | flattened overlay" type-checked any value at all,
+including bodies the schema refuses. It is now the union of the input types of
+`VIEW_METADATA_MEMBERS`, the four members the schema's union runs, so `unknown`, a non-object and a
+key no member declares are compile errors, and a body of each member still type-checks.
+
+**What still differs from the runtime verdict.** The type is the members' declared shape, not the
+door's answer. The door still accepts bodies the type refuses (it removes the console's row `id`s
+and three members strip undeclared keys), and still refuses bodies the type admits (the identity
+precondition, the members' refinements, and a body mixing keys of different members, which
+TypeScript checks against the union as a whole). `ViewMetadataSchema.safeParse` remains the only
+judge.
+
+**If your code stops compiling.** A value you annotated as `ViewMetadata` is not one of the four
+member shapes. Correct the body, or type a value that is still unvalidated as `unknown` and let
+`ViewMetadataSchema.safeParse` decide.
+
+`ViewMetadataParsed` is not changed by this release: it is still `unknown`.
+
+<!-- adr-0087: not-required (no-migration-prescription) Nothing authorable is removed, renamed or re-typed at runtime: no spec key, no export, no stored row moves, and every view body parses byte-identically, so `objectstack migrate meta` has nothing to reach. The only thing that moved is a TypeScript annotation, whose channel is the consumer's compiler. `type-surface-only` does not apply because this diff touches `packages/spec/**` (its predicate 2). -->