feat(spool): add default methods to CloudMessageSpool for fast startu…

src/main/java/com/aws/greengrass/mqttclient/spool/CloudMessageSpool.java

@@ -6,6 +6,7 @@
 package com.aws.greengrass.mqttclient.spool;
 
 import java.io.IOException;
+import java.util.List;
 
 public interface CloudMessageSpool {
 
@@ -17,5 +18,34 @@ public interface CloudMessageSpool {
 
     Iterable<Long> getAllMessageIds() throws IOException;
 
+    /**
+     * Get the maximum message ID currently stored in the spool.
+     * This is used to set the next ID for new messages without iterating all messages.
+     *
+     * <p>Default returns -1 (not supported) for backward compatibility with older plugin versions.
+     * When -1 is returned, the nucleus falls back to iterating all message IDs.</p>
+     *
+     * @return the maximum message ID, or -1 if the spool is empty or not supported
+     * @throws IOException if an I/O error occurs
+     */
+    default long getMaxMessageId() throws IOException {
+        return -1;
+    }
+
+    /**
+     * Get all message IDs with their payload sizes, ordered by ID ascending.
+     * Returns a list of [messageId, payloadSizeInBytes] pairs without reading full payloads.
+     * This enables fast capacity tracking during startup without per-message I/O.
+     *
+     * <p>Default returns null (not supported) for backward compatibility with older plugin versions.
+     * When null is returned, the nucleus falls back to reading each message individually.</p>
+     *
+     * @return ordered list of (id, size) pairs, or null if not supported
+     * @throws IOException if an I/O error occurs
+     */
+    default List<long[]> getAllMessageIdsWithSizes() throws IOException {
+        return null;
+    }
+
     void initializeSpooler() throws IOException;
 }