fix(files): preserve scroll position during Mothership streaming edits

Two fixes to the Monaco auto-scroll logic:

1. At streaming start, initialize textareaStuckRef from the editor's actual
   scroll position (isAtBottom check) instead of unconditionally setting true.
   Previously every streaming session jumped the viewport to the last line on
   the very first content update, even when the user was reading mid-file.

2. Replace the wheel-only DOM listener with editor.onDidScrollChange(), the
   proper Monaco API. This covers trackpad, scrollbar drag, and keyboard scroll
   — not just mouse wheel. As a bonus, scrolling back to the bottom during
   streaming now re-engages follow mode (matching iTerm2/xterm.js behavior).

3. Save and restore view state around model.setValue() during streaming when
   the user has scrolled away from the bottom. This prevents Monaco from
   resetting the viewport on each content replacement. When the user is at
   the bottom, view state is not saved so Effect 3 can scroll to the new bottom.

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/files/components/file-viewer/file-viewer.tsx

@@ -852,7 +852,12 @@ function TextEditor({
     if (monacoValue === content) return
 
     if (isStreamInteractionLocked || monacoValue === lastSyncedContentRef.current) {
+      // Preserve the user's scroll position during streaming updates, unless they
+      // are already at the bottom (in which case Effect 3 will scroll to the new bottom).
+      const viewState =
+        isStreamInteractionLocked && !textareaStuckRef.current ? editor.saveViewState() : null
       model.setValue(content)
+      if (viewState) editor.restoreViewState(viewState)
       lastSyncedContentRef.current = content
     }
   }, [content, isStreamInteractionLocked])
@@ -865,20 +870,23 @@ function TextEditor({
       return
     }
 
-    textareaStuckRef.current = true
-    const domNode = editor.getDomNode()
-    if (!domNode) return
+    const isAtBottom = () => {
+      const scrollTop = editor.getScrollTop()
+      const scrollHeight = editor.getScrollHeight()
+      const { height } = editor.getLayoutInfo()
+      return scrollHeight - scrollTop - height < 80
+    }
 
-    const scrollable = domNode.querySelector('.monaco-scrollable-element') as HTMLElement | null
-    if (!scrollable) return
+    // Initialize from actual position — only follow if already at the bottom.
+    textareaStuckRef.current = isAtBottom()
 
-    const onWheel = (e: Event) => {
-      if ((e as WheelEvent).deltaY < 0) textareaStuckRef.current = false
-    }
-    scrollable.addEventListener('wheel', onWheel, { passive: true })
+    // Use Monaco's scroll API so trackpad, scrollbar drag, and keyboard all update the flag.
+    const disposable = editor.onDidScrollChange(() => {
+      textareaStuckRef.current = isAtBottom()
+    })
 
     return () => {
-      scrollable.removeEventListener('wheel', onWheel)
+      disposable.dispose()
     }
   }, [isStreamInteractionLocked, disableStreamingAutoScroll])