Add consent-gated media exchange library

docs/architecture.md

@@ -58,7 +58,8 @@ SIGINT/SIGTERM abort shared loops, stop account runtimes, stop the web server, c
 - Reddit request coordinator (shared across runtime construction);
 - recipient history/reservations across accounts;
 - Express server, dashboard assets, event stream, and operational jobs;
-- configured subreddit catalog and application policy.
+- configured subreddit catalog and application policy;
+- shared operator-owned exchange library, classification metadata, and outbound-use ledger;
 
 ### Account-scoped
 
@@ -132,6 +133,7 @@ docs/                          Maintainer and agent documentation
 - New transport field: define it in `packages/api-contracts`, return it from the route, consume it in the dashboard, and add contract/route/UI tests.
 - New API operation: add a focused router, register it in `src/web/server.ts`, describe it in `src/web/api-catalog.ts`, regenerate `docs/api.md`, and add authorization tests.
 - New persisted state: add an append-only migration, expose it through a small repository, and test fresh plus upgraded databases.
+- Shared operator media: keep it under `MediaLibraryService`/`MediaLibraryRepository`; never merge it with account-owned received media.
 - New account behavior: place it in the account runtime or a service injected into it; do not add mutable cross-account identity to a singleton.
 - New candidate stage: make transitions durable and idempotent, expose counts/reasons, and define lease/retry behavior.
 - New dashboard feature: add a feature slice and route, use shared schemas and query keys, and treat HTTP as authoritative.