fix: prevent stale windowStart when switching conversations

src/lib/components/Terminal.svelte

@@ -59,20 +59,27 @@
 
     currentConversationId = newId;
 
+    // Peek at the saved position to set windowStart before the first tick,
+    // preventing a stale windowStart from a previous conversation leaving
+    // visibleLines empty (windowStart >= lines.length).
+    const savedPosition = claudeStore.getScrollPosition(newId);
+    if (savedPosition === -1) {
+      // Will auto-scroll: pin the window to the tail of the new conversation
+      shouldAutoScroll = true;
+      windowStart = Math.max(0, lines.length - WINDOW_SIZE);
+    } else {
+      // Will restore a specific position: always start from the top of history
+      shouldAutoScroll = false;
+      windowStart = 0;
+    }
+
     // Restore scroll position for the new conversation after DOM updates
     await tick();
     if (terminalElement) {
-      const savedPosition = claudeStore.getScrollPosition(newId);
       isRestoringScroll = true;
       if (savedPosition === -1) {
-        // Auto-scroll to bottom — window reactive statement will advance windowStart
-        shouldAutoScroll = true;
         terminalElement.scrollTop = terminalElement.scrollHeight;
       } else {
-        // Restore to saved position — show from the beginning of history
-        windowStart = 0;
-        shouldAutoScroll = false;
-        await tick();
         terminalElement.scrollTop = savedPosition;
       }
       // Small delay to prevent the scroll handler from overriding our restore