fix: resolve New Relic ghost traffic and blind APM transaction naming

Three root causes addressed:

1. nginx routing gap — bare GET /api (no trailing slash) fell through
   `location /api/` to the Vite dev proxy, which forwarded it to the
   backend as an unmatched path. Added `location = /api` exact-match
   block before the prefix block to catch it and proxy directly to
   the backend health handler.

2. AppController root handler — added @Get() (maps to GET /api with
   global prefix) so bare /api requests return a clean 200 instead of
   a 404 that registers as a phantom NR transaction.

3. New Relic transaction naming — NestJS's setGlobalPrefix('api')
   causes NR's Express instrumentation to bucket ALL requests into the
   generic "Expressjs/GET/api$" segment, making per-endpoint APM data
   completely useless. The new NewRelicTransactionInterceptor calls
   newrelic.setTransactionName() with "METHOD /route/pattern" for
   every request (after routing, so req.route is populated with the
   matched template). Gracefully no-ops in dev where NR is not loaded.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/app.controller.ts

@@ -2,6 +2,23 @@ import { Controller, Get } from '@nestjs/common';
 
 @Controller()
 export class AppController {
+  /**
+   * GET /api — bare root of the API.
+   * Handles requests that omit the trailing slash so nginx's `location /api/`
+   * block (which requires a trailing slash) doesn't fall through to the Vite
+   * frontend proxy.  Also gives New Relic and health checkers a real 200 rather
+   * than a 404 that would register as a phantom transaction.
+   */
+  @Get()
+  getRoot() {
+    return {
+      status: 'ok',
+      timestamp: new Date().toISOString(),
+      service: 'hoa-financial-platform',
+    };
+  }
+
+  /** GET /api/health — explicit named health endpoint for uptime monitors */
   @Get('health')
   getHealth() {
     return {

backend/src/app.module.ts

@@ -9,6 +9,7 @@ import { TenantMiddleware } from './database/tenant.middleware';
 import { WriteAccessGuard } from './common/guards/write-access.guard';
 import { CapabilityGuard } from './common/guards/capability.guard';
 import { NoCacheInterceptor } from './common/interceptors/no-cache.interceptor';
+import { NewRelicTransactionInterceptor } from './common/interceptors/newrelic-transaction.interceptor';
 import { AuthModule } from './modules/auth/auth.module';
 import { OrganizationsModule } from './modules/organizations/organizations.module';
 import { UsersModule } from './modules/users/users.module';
@@ -109,6 +110,10 @@ import { ScheduleModule } from '@nestjs/schedule';
       provide: APP_INTERCEPTOR,
       useClass: NoCacheInterceptor,
     },
+    {
+      provide: APP_INTERCEPTOR,
+      useClass: NewRelicTransactionInterceptor,
+    },
   ],
 })
 export class AppModule implements NestModule {

backend/src/common/interceptors/newrelic-transaction.interceptor.ts

@@ -0,0 +1,46 @@
+import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';
+import { Observable } from 'rxjs';
+import { Request } from 'express';
+
+/**
+ * Sets a meaningful New Relic transaction name for every HTTP request.
+ *
+ * Without this, NestJS's setGlobalPrefix('api') causes the New Relic Express
+ * instrumentation to group ALL requests under the generic bucket
+ * "Expressjs/GET/api$" (the compiled regex for the global prefix router),
+ * making per-endpoint APM data completely blind.
+ *
+ * This interceptor runs after NestJS routing (so req.route is populated with
+ * the matched pattern, e.g. "/api/accounts/:id") and calls newrelic.setTransactionName()
+ * to override the auto-detected name with "METHOD /route/pattern".
+ *
+ * Gracefully no-ops when:
+ *  - NEW_RELIC_ENABLED is not 'true' (dev / CI)
+ *  - newrelic package is not installed
+ *  - The NR agent fails to load for any reason
+ */
+
+let newrelic: any;
+try {
+  if (process.env.NEW_RELIC_ENABLED === 'true') {
+    // eslint-disable-next-line @typescript-eslint/no-require-imports
+    newrelic = require('newrelic');
+  }
+} catch {
+  // Package not installed in this environment — skip instrumentation silently
+}
+
+@Injectable()
+export class NewRelicTransactionInterceptor implements NestInterceptor {
+  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
+    if (newrelic) {
+      const req = context.switchToHttp().getRequest<Request>();
+      // req.route.path is the Express matched route template (e.g. "/api/accounts/:id").
+      // Falls back to req.path (the actual URL) for unmatched requests so even
+      // 404s get a useful name like "GET /api/unknown-path" instead of "Expressjs/GET/api$".
+      const route: string = (req.route as any)?.path ?? req.path;
+      newrelic.setTransactionName(`${req.method} ${route}`);
+    }
+    return next.handle();
+  }
+}