Generate and reauthorize composite-key and read-only Changed subscriptions #191

Generated subscription qualification currently has an implementation prerequisite. Source inspection at workspace-2026.10.20.4, workspace-2026.10.22.1 and main a90b5bd finds __gom_composite_key_subscriptions_unavailable: composite-key entities receive only a hidden empty stream. The catalogue does not describe a Changed field. The same stub branch omits real subscriptions for external_read_only entities on SQLite/PostgreSQL. No local compiler/runtime reproduction is claimed; native grants are held.

Composite-key reproducer: derive GraphQLEntity/GraphQLOperations for a two-primary-key SQLite entity and compose it with schema_roots. A real Changed field is absent, so per-event revocation cannot yet be qualified. MSSQL source/SDL differences need their own explicit backend tests; existing issue #118 alone does not establish subscription support.

Required work:

• Emit typed complete composite target identity, trusted after-commit witness and source identity without conflating rows sharing the first key component.
• Generate the same request/entity/row/selected-field/assurance/provenance revalidation for every release. Key filters must compare complete keys. Denied or missing current rows and failed checks suppress the whole event.
• Keep generated mutations/schema ownership independent. Read-only projection subscriptions must accept only trusted ORM propagation events, never raw/deserialized observer events or an external write capability.
• Prove direct and child→parent events, colliding composite keys, source/target revocation after registration, rollback, deleted preimage rules, cycles/hop budgets and catalogue/SDL parity on each supported backend using disposable fixtures.

The read-only part blocks safe AI-owned metadata projections in #184 / draft #189: private-source→projection notifications plus message→session/run propagation are still missing. Do not treat a native stream, raw persistence re-export, shadow table or tests-only PR as a completion. Existing downstream roots remain ledgered until a qualified approved release.