refactor(#747): de-hardcode interaction coordination names

apps/gateway/src/agent/durable-session.dto.ts

@@ -0,0 +1,10 @@
+import type { RuntimeProviderRequestContext } from './runtime-provider-registry.service.js';
+
+/** Server-side request for a replay-safe provider message. */
+export interface ProviderOutboxDto {
+  sessionId: string;
+  idempotencyKey: string;
+  correlationId: string;
+  content: string;
+  context: RuntimeProviderRequestContext;
+}