ui: the readouts strip is also shown in a collapsed window

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ui.cpp

@@ -4013,10 +4013,14 @@ gboolean tick(gpointer user) {
         app->sidebar_syncing = false;
       }
     }
-    // The readouts strip is on screen exactly when the dock is not. Decided here, right after the wish was
-    // re-asserted and *before* the collapsing below (which makes the split view write `show-sidebar`
-    // false itself until the next frame re-asserts it): read after it, the strip would show for one frame
-    // each time the window narrowed.
+    // The readouts strip is on screen when the dock is not beside the plot: `!show-sidebar || collapsed`.
+    // Decided here, right after the wish was re-asserted and *before* the collapsing below (which makes
+    // the split view write `show-sidebar` false itself until the next frame re-asserts it): read after
+    // it, `show-sidebar` would be that transient false. The strip reads `collapsed` too, and here that is
+    // the previous frame's value (`set_collapsed()` follows): on a collapse or a widening the strip
+    // changes one tick after the split view does, but never to a wrong state -- `show-sidebar` is always
+    // the re-asserted wish and `collapsed` a settled value -- so it does not flash. Moving the call after
+    // `set_collapsed()` would bring back the transient `show-sidebar` for nothing.
     sync_readouts_strip(*app);
     const int window_w = gtk_widget_get_width(app->window);
     if (window_w > 0) {