Fix scroll-to-bottom on page load/refresh in builder page

The scroll-to-bottom functionality wasn't working properly on page load because
messages take time to load and render. This fix adds:

- Enhanced scrollChatToBottom() with image load detection
- ResizeObserver to detect content height changes
- Multiple scroll attempts with increasing delays (up to 2s)
- Additional scroll calls in selectSessionById with proper delays
- Scroll calls at end of initBuilder initialization

This ensures the chat area properly scrolls to the bottom even when content
loads asynchronously or images take time to render.

chat/public/builder.js

@@ -1520,7 +1520,7 @@ function closeHistoryModal() {
   if (el.historyModal) el.historyModal.style.display = 'none';
 }
 
-function scrollChatToBottom() {
+function scrollChatToBottom(force = false) {
   if (!el.chatArea) return;
   const target = el.chatArea;
   
@@ -1533,14 +1533,18 @@ function scrollChatToBottom() {
   // 1. Immediate scroll attempt
   doScroll();
   
-  // 2. After a short delay to allow DOM updates
+  // 2. After short delays to allow DOM updates
   setTimeout(() => { doScroll(); }, 10);
   setTimeout(() => { doScroll(); }, 50);
   setTimeout(() => { doScroll(); }, 100);
   setTimeout(() => { doScroll(); }, 250);
   setTimeout(() => { doScroll(); }, 500);
   
-  // 3. Use requestAnimationFrame for smooth scrolling
+  // 3. Longer delay for content to fully settle (especially on page load)
+  setTimeout(() => { doScroll(); }, 1000);
+  setTimeout(() => { doScroll(); }, 2000);
+  
+  // 4. Use requestAnimationFrame for smooth scrolling
   requestAnimationFrame(() => {
     doScroll();
     requestAnimationFrame(() => {
@@ -1551,22 +1555,65 @@ function scrollChatToBottom() {
     });
   });
 
-  // 4. Scroll when images load (if any)
+  // 5. Wait for ALL images to load before scrolling
   const images = target.querySelectorAll('img');
+  let imagesToLoad = 0;
+  
   images.forEach((img) => {
     if (!img.complete) {
-      img.addEventListener('load', () => doScroll(), { once: true });
+      imagesToLoad++;
+      img.addEventListener('load', () => {
+        imagesToLoad--;
+        doScroll();
+        // Scroll again after a short delay to ensure layout is updated
+        setTimeout(() => doScroll(), 100);
+      }, { once: true });
+      
+      img.addEventListener('error', () => {
+        imagesToLoad--;
+        doScroll();
+      }, { once: true });
     }
   });
   
-  // 5. Also scroll when any content finishes rendering (using MutationObserver)
+  // If there are images loading, scroll again after they all complete
+  if (imagesToLoad > 0) {
+    const checkImagesLoaded = setInterval(() => {
+      if (imagesToLoad === 0) {
+        clearInterval(checkImagesLoaded);
+        doScroll();
+        setTimeout(() => doScroll(), 100);
+        setTimeout(() => doScroll(), 500);
+      }
+    }, 100);
+    
+    // Stop checking after 5 seconds to avoid infinite interval
+    setTimeout(() => clearInterval(checkImagesLoaded), 5000);
+  }
+  
+  // 6. Use ResizeObserver to detect when content height changes
+  if (typeof ResizeObserver !== 'undefined') {
+    const resizeObserver = new ResizeObserver((entries) => {
+      for (const entry of entries) {
+        if (entry.target === target) {
+          doScroll();
+        }
+      }
+    });
+    resizeObserver.observe(target);
+    
+    // Stop observing after a while
+    setTimeout(() => resizeObserver.disconnect(), 3000);
+  }
+  
+  // 7. Also scroll when any content finishes rendering (using MutationObserver)
   if (typeof MutationObserver !== 'undefined') {
     const observer = new MutationObserver(() => {
       doScroll();
     });
     observer.observe(target, { childList: true, subtree: true });
     // Stop observing after a while to avoid memory leaks
-    setTimeout(() => observer.disconnect(), 2000);
+    setTimeout(() => observer.disconnect(), 3000);
   }
 }
 
@@ -2775,15 +2822,20 @@ window.selectSessionById = async function(id) {
     console.log('[BUILDER] Rendering UI with fresh session data');
     renderSessionMeta(freshSession);
     renderMessages(freshSession);
-    // Add a small delay to ensure DOM is updated before scrolling
+    // Wait for content to fully render before scrolling
-    setTimeout(() => scrollChatToBottom(), 50);
+    // Use multiple delays to catch content that loads asynchronously
+    setTimeout(() => scrollChatToBottom(), 100);
+    setTimeout(() => scrollChatToBottom(), 500);
+    setTimeout(() => scrollChatToBottom(), 1000);
   } else {
     // If refresh failed, use the local session data instead
     console.warn('[BUILDER] Using local session data for UI render');
     renderSessionMeta(session);
     renderMessages(session);
-    // Add a small delay to ensure DOM is updated before scrolling
+    // Wait for content to fully render before scrolling
-    setTimeout(() => scrollChatToBottom(), 50);
+    setTimeout(() => scrollChatToBottom(), 100);
+    setTimeout(() => scrollChatToBottom(), 500);
+    setTimeout(() => scrollChatToBottom(), 1000);
   }
   
   // Update URL to reflect the new session (but don't reload page)
@@ -4557,6 +4609,12 @@ window.addEventListener('focus', () => {
 
   // Load provider limits for fallback model selection
   loadProviderLimits();
+  
+  // Scroll to bottom after initialization completes - use multiple delays
+  // to catch content that renders asynchronously
+  setTimeout(() => scrollChatToBottom(), 500);
+  setTimeout(() => scrollChatToBottom(), 1000);
+  setTimeout(() => scrollChatToBottom(), 2000);
 })();
 
 async function loadProviderLimits() {