fix(image-hook): reset checkpoint after history compaction

When OpenCode compacts conversation history, userMsgCount can drop below
the stored lastProcessed counter, causing the guard to skip new images
without warning. Reset the checkpoint when the count falls below the
stored value.

src/hooks/image-hook.ts

@@ -202,7 +202,12 @@ export function processImageAttachments(args: {
     const sessionId = firstUserMsg?.info.sessionID ?? 'default';
     const counterKey = `${workDir}:${sessionId}`;
     const userMsgCount = messages.filter(isUserMessageWithParts).length;
-    const lastProcessed = lastProcessedUserMsgCountByDir.get(counterKey) ?? 0;
+    let lastProcessed = lastProcessedUserMsgCountByDir.get(counterKey) ?? 0;
+    // ponytail: reset after history compaction; re-checking old messages is harmless
+    if (userMsgCount < lastProcessed) {
+      lastProcessed = 0;
+      lastProcessedUserMsgCountByDir.set(counterKey, 0);
+    }
     if (userMsgCount > lastProcessed) {
       // Check only the new user messages (those we haven't seen yet)
       let userIndex = 0;