actions/action_registry.ts

ActionRegistry — query and filter utility over ActionSpecUnion[].

Vocabulary (see the docs/ directory):

• *_handled_* — request_response specs the named side receives (so the named side owns the handler). Used by codegen to emit typed handler maps.
• *_relevant_to_* — the loose "everything this side might encounter" set, used by the typed-Proxy method enums (FrontendActionMethod, BackendActionMethod).
• broadcast_* — kind-narrow remote_notification set with the streams-target exclusion. Today this matches what the broadcast API exposes.
• backend_initiated_* — forward-looking kind-agnostic version of the broadcast set. Same content today; will diverge when local_calls or backend request_response join the backend's typed surface.

Cache discipline: spec_by_method (Map) and the internal streams-target set lazy-memoize because the Map is consulted per-RPC dispatch (actions/frontend_rpc_client.ts wires it into lookup_action_spec) and the streams set is rebuilt by two public getters. Array-returning getters recompute on each call so callers can mutate the result freely (.sort(), .push(injected) on a copy, etc.) without affecting the registry — codegen is a build-time path where the extra .filter / .map work is negligible.