UI: Preserve chat scroll position on textarea resize

js/main.js

@@ -1065,3 +1065,57 @@ document.fonts.addEventListener("loadingdone", (event) => {
     }
   }, 50);
 });
+
+//------------------------------------------------
+// Preserve chat scroll position on textarea resize
+//------------------------------------------------
+(function() {
+  let chatParent = null;
+  let initialState = null;
+  let debounceTimeout = null;
+
+  function getChatParent() {
+    if (!chatParent) chatParent = document.querySelector(".chat-parent");
+    return chatParent;
+  }
+
+  function getTextarea() {
+    return document.querySelector("#chat-input textarea");
+  }
+
+  document.addEventListener("input", function(e) {
+    if (e.target.matches("#chat-input textarea")) {
+      const chat = getChatParent();
+      const textarea = getTextarea();
+
+      if (chat && textarea) {
+        // Capture initial state only on first input of a typing sequence
+        if (!initialState) {
+          initialState = {
+            scrollTop: chat.scrollTop,
+            textareaHeight: textarea.offsetHeight
+          };
+        }
+
+        // Clear existing timeout
+        clearTimeout(debounceTimeout);
+
+        // Wait for typing to stop (50ms delay)
+        debounceTimeout = setTimeout(() => {
+          const finalTextareaHeight = textarea.offsetHeight;
+          const totalGrowth = finalTextareaHeight - initialState.textareaHeight;
+          const targetScroll = initialState.scrollTop + totalGrowth;
+
+          const restore = () => { chat.scrollTop = targetScroll; };
+
+          restore();
+          requestAnimationFrame(restore);
+          setTimeout(restore, 0);
+          setTimeout(restore, 10);
+
+          initialState = null;
+        }, 50);
+      }
+    }
+  }, true);
+})();