Add analytics batch cap and request deduplication interceptor

src/analytics/services/batch-size-guard.service.ts

@@ -0,0 +1,23 @@
+import { Injectable } from '@nestjs/common';
+
+@Injectable()
+export class BatchSizeGuardService {
+  private readonly maxSize: number = 10000;
+  private droppedCount: number = 0;
+
+  canAdd(currentSize: number): boolean {
+    if (currentSize >= this.maxSize) {
+      this.droppedCount++;
+      return false;
+    }
+    return true;
+  }
+
+  getDroppedCount(): number {
+    return this.droppedCount;
+  }
+
+  resetDroppedCount(): void {
+    this.droppedCount = 0;
+  }
+}

src/common/interceptors/request-dedup.interceptor.ts

@@ -0,0 +1,33 @@
+import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';
+import { Observable, of } from 'rxjs';
+import { tap } from 'rxjs/operators';
+
+@Injectable()
+export class RequestDedupInterceptor implements NestInterceptor {
+  private cache = new Map<string, { response: any; timestamp: number }>();
+  private readonly ttlMs = 60000;
+
+  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
+    const req = context.switchToHttp().getRequest();
+    if (req.method !== 'POST') return next.handle();
+
+    const key = this.fingerprint(req);
+    const cached = this.cache.get(key);
+    if (cached && Date.now() - cached.timestamp < this.ttlMs) {
+      const res = context.switchToHttp().getResponse();
+      res.setHeader('X-Duplicate-Request', 'true');
+      return of(cached.response);
+    }
+
+    return next.handle().pipe(
+      tap((response) => {
+        this.cache.set(key, { response, timestamp: Date.now() });
+      }),
+    );
+  }
+
+  private fingerprint(req: any): string {
+    const id = req.user ? req.user.id : 'anon';
+    return `${req.method}:${req.path}:${JSON.stringify(req.body)}:${id}`;
+  }
+}