fix(PLU-308): chat agent scroll jump fix

reai_toolkit/app/components/tabs/chat_tab.py

@@ -176,6 +176,7 @@ def __init__(self, on_closed: Optional[Callable[[], None]] = None) -> None:
         self._render_timer: Optional[QtCore.QTimer] = None
         self._pending_state: Optional[ChatState] = None
         self._pending_confirm_id: Optional[str] = None
+        self._last_rendered_md: Optional[str] = None
 
     def Create(self, title) -> bool:
         flags = getattr(kw.PluginForm, "WOPN_DP_TAB", 0) | getattr(
@@ -332,14 +333,21 @@ def _flush_render(self) -> None:
             return
 
         sb = self._transcript.verticalScrollBar()
+        prev = sb.value() if sb is not None else 0
         at_bottom = sb is None or sb.value() >= sb.maximum() - 4
         md = render_transcript_markdown(state)
-        if hasattr(self._transcript, "setMarkdown"):
-            self._transcript.setMarkdown(md)
-        else:
-            self._transcript.setPlainText(md)
-        if at_bottom and sb is not None:
-            sb.setValue(sb.maximum())
+        # Rebuilding the whole document resets the scrollbar to the top, so only
+        # do it when the content actually changed, and afterwards keep the reader
+        # where they were: pinned to the bottom if they were following the stream,
+        # otherwise restored to their previous position instead of snapping up.
+        if md != self._last_rendered_md:
+            self._last_rendered_md = md
+            if hasattr(self._transcript, "setMarkdown"):
+                self._transcript.setMarkdown(md)
+            else:
+                self._transcript.setPlainText(md)
+            if sb is not None:
+                sb.setValue(sb.maximum() if at_bottom else prev)
 
         running = state.run_status == "running"
         if self._send_btn is not None: