defineMapping artifacts are registered but never consumed — wire named mappings into REST import or de-scope from the stack

[os-zhuang]

defineMapping / the stack mappings: collection is registered as metadata (engine metadataArrayKeys, packages/metadata/src/plugin.ts), but no runtime consumer resolves a named mapping: the REST import path (packages/rest/src/rest-server.ts, data-import handler) only accepts an inline per-request mapping body param — it never looks up a registered mapping artifact by name.

So a defineMapping entry in an app stack is inert: it parses, registers, and does nothing.

Found while upgrading the showcase to a registry-driven coverage manifest. Per Prime Directive #10 the showcase must not demo inert capabilities, so mappings is recorded as an explicit waiver in STACK_COLLECTION_COVERAGE (examples/app-showcase/src/coverage.ts) pointing at this issue. (app-crm does ship a defineMapping example — examples/app-crm/src/data/crm-mappings.ts — which today is declared-but-not-enforced.)

Resolution options:

1. Wire it: let the REST import/export endpoints accept mappingName and resolve the registered artifact (contract-first: the artifact becomes the source of truth, inline stays as an escape hatch), or
2. De-scope: drop mappings from the stack schema until there is a consumer, and migrate app-crm's example.

Once either lands, flip the showcase waiver to demonstrated.