Add centralized pipeline fallback notifier

src/ai/user-request-pipeline/fallback-notifier-registry.ts

@@ -0,0 +1,16 @@
+import type {PipelineFallbackDecision} from "./fallback-executor.js";
+
+export function fallbackNotificationKey(requestId: string, decision: PipelineFallbackDecision): string {
+    return `${requestId}:${decision.stage}:${decision.action}`;
+}
+
+export class PipelineFallbackNotificationRegistry {
+    private readonly notifiedKeys = new Set<string>();
+
+    claim(requestId: string, decision: PipelineFallbackDecision): boolean {
+        const key = fallbackNotificationKey(requestId, decision);
+        if (this.notifiedKeys.has(key)) return false;
+        this.notifiedKeys.add(key);
+        return true;
+    }
+}