fix: Prevent cold-path JVM/Hibernate latency after extended idle periods

backend/src/main/java/com/threeriversbank/ThreeRiversBankApplication.java

@@ -3,9 +3,11 @@
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.cloud.openfeign.EnableFeignClients;
+import org.springframework.scheduling.annotation.EnableScheduling;
 
 @SpringBootApplication
 @EnableFeignClients
+@EnableScheduling
 public class ThreeRiversBankApplication {
 
     public static void main(String[] args) {

backend/src/main/java/com/threeriversbank/service/WarmupService.java

@@ -0,0 +1,31 @@
+package com.threeriversbank.service;
+
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.scheduling.annotation.Scheduled;
+import org.springframework.stereotype.Service;
+
+@Service
+@RequiredArgsConstructor
+@Slf4j
+public class WarmupService {
+
+    private final CreditCardService creditCardService;
+
+    /**
+     * Periodically calls getAllCreditCards() to keep the JVM hot, Hibernate query plan
+     * cache warm, and the H2 HikariCP connection pool active after idle periods.
+     * Runs every 5 minutes (300,000 ms) with a 1-minute (60,000 ms) initial delay.
+     * Delays are configurable via warmup.fixed-delay and warmup.initial-delay properties.
+     */
+    @Scheduled(fixedDelayString = "${warmup.fixed-delay}", initialDelayString = "${warmup.initial-delay}")
+    public void warmup() {
+        log.debug("WarmupService: running scheduled warmup to keep JVM and Hibernate hot");
+        try {
+            int count = creditCardService.getAllCreditCards().size();
+            log.debug("WarmupService: warmup complete, {} cards loaded", count);
+        } catch (Exception e) {
+            log.warn("WarmupService: warmup query failed: {}", e.getMessage());
+        }
+    }
+}

backend/src/main/resources/application.yml

@@ -7,6 +7,10 @@ spring:
     driver-class-name: org.h2.Driver
     username: sa
     password: 
+    hikari:
+      connection-test-query: SELECT 1
+      keepalive-time: 300000ms
+      idle-timeout: 600000ms
 
   h2:
     console:
@@ -17,7 +21,7 @@ spring:
     database-platform: org.hibernate.dialect.H2Dialect
     hibernate:
       ddl-auto: create
-    show-sql: true
+    show-sql: false
     defer-datasource-initialization: true
 
   sql:
@@ -80,3 +84,8 @@ springdoc:
     path: /api-docs
   swagger-ui:
     path: /swagger-ui.html
+
+# Warmup scheduler configuration
+warmup:
+  fixed-delay: 300000
+  initial-delay: 60000