feat(idempotency): add automatic priming for DynamoDB persistence store

Implements automatic class preloading via CRaC hooks for the
idempotency-dynamodb module to improve SnapStart cold start performance.

Changes:
- Add ClassPreLoader.preloadClasses() call to DynamoDBPersistenceStore.beforeCheckpoint()
- Generate and include classesloaded.txt with 8,726 classes
- Add powertools-common dependency for ClassPreLoader
- Add Maven profile generate-classesloaded-file
- Add unit tests for CRaC hooks
- Update Priming.md with idempotency-dynamodb example
- Add null check and logging for defensive error handling

This combines both invoke priming (warming DynamoDB SDK paths)
and automatic priming (preloading classes) for optimal performance.

Follows the same pattern as implemented in powertools-metrics (#1861),
powertools-tracing (#2345), and powertools-kafka (#2145).

Fixes #1997

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: dcabib

Priming.md

@@ -56,4 +56,6 @@ In order to generate the `classloaded.txt` file for a Java module in this projec
 - `classesloaded.txt` file includes test classes as well because the file is generated while running tests. This is not a problem because all the classes that are not found are ignored by `ClassPreLoader.preloadClasses()`. Also `beforeCheckpoint()` hook is not time-sensitive, it only runs once when a new Lambda version gets published. 
 
 ## Reference Implementation
-Working example is available in the [powertools-metrics](powertools-metrics/src/main/java/software/amazon/lambda/powertools/metrics/MetricsFactory.java). 
+Working examples are available in:
+- [powertools-metrics](powertools-metrics/src/main/java/software/amazon/lambda/powertools/metrics/MetricsFactory.java) - Automatic priming with `ClassPreLoader`
+- [powertools-idempotency-dynamodb](powertools-idempotency/powertools-idempotency-dynamodb/src/main/java/software/amazon/lambda/powertools/idempotency/persistence/dynamodb/DynamoDBPersistenceStore.java) - Invoke priming + Automatic priming 

powertools-idempotency/powertools-idempotency-dynamodb/pom.xml

@@ -65,6 +65,10 @@
             <groupId>org.crac</groupId>
             <artifactId>crac</artifactId>
         </dependency>
+        <dependency>
+            <groupId>software.amazon.lambda</groupId>
+            <artifactId>powertools-common</artifactId>
+        </dependency>
 
         <!-- Test dependencies -->
         <dependency>
@@ -106,6 +110,24 @@
     </dependencies>
 
     <profiles>
+        <profile>
+            <id>generate-classesloaded-file</id>
+            <build>
+                <plugins>
+                    <plugin>
+                        <groupId>org.apache.maven.plugins</groupId>
+                        <artifactId>maven-surefire-plugin</artifactId>
+                        <configuration>
+                            <argLine>
+                                -Xlog:class+load=info:classesloaded.txt
+                                --add-opens java.base/java.util=ALL-UNNAMED
+                                --add-opens java.base/java.lang=ALL-UNNAMED
+                            </argLine>
+                        </configuration>
+                    </plugin>
+                </plugins>
+            </build>
+        </profile>
         <profile>
             <id>generate-graalvm-files</id>
             <!-- The AWS DynamoDBClient uses com.amazonaws.xray.interceptors.TracingInterceptor if available on the

powertools-idempotency/powertools-idempotency-dynamodb/src/main/java/software/amazon/lambda/powertools/idempotency/persistence/dynamodb/DynamoDBPersistenceStore.java

@@ -30,6 +30,7 @@
 import software.amazon.awssdk.services.dynamodb.model.GetItemResponse;
 import software.amazon.awssdk.services.dynamodb.model.PutItemRequest;
 import software.amazon.awssdk.services.dynamodb.model.UpdateItemRequest;
+import software.amazon.lambda.powertools.common.internal.ClassPreLoader;
 import software.amazon.lambda.powertools.common.internal.UserAgentConfigurator;
 import software.amazon.lambda.powertools.idempotency.Constants;
 import software.amazon.lambda.powertools.idempotency.exceptions.IdempotencyItemAlreadyExistsException;
@@ -123,7 +124,13 @@ private DynamoDBPersistenceStore(String tableName,
      */
     @Override
     public void beforeCheckpoint(org.crac.Context<? extends Resource> context) throws Exception {
+        // Skip priming if DynamoDB client is not available
+        if (dynamoDbClient == null) {
+            return;
+        }
+
         try {
+            // Invoke priming - exercise DynamoDB SDK paths
             String primingRecordKey = "__invoke_prime__";
             Instant now = Instant.now();
             long expiry = now.plus(3600, ChronoUnit.SECONDS).getEpochSecond();
@@ -137,8 +144,12 @@ public void beforeCheckpoint(org.crac.Context<? extends Resource> context) throw
             putRecord(primingDataRecord, Instant.now());
             getRecord(primingRecordKey);
             deleteRecord(primingRecordKey);
-        } catch (Exception unknown) {
-            // This is unexpected but we must continue without any interruption
+
+            // Automatic priming - preload classes from classesloaded.txt
+            ClassPreLoader.preloadClasses();
+        } catch (Exception e) {
+            // Log the exception for debugging but continue to ensure checkpoint succeeds
+            LOG.warn("Priming failed during checkpoint, continuing anyway", e);
         }
     }