Keep allocation destinations readable without blocking collapsed header drops

crates/oa-desktop/src/views.rs

@@ -510,6 +510,31 @@ fn diagram(app: &App) -> View<'_, Message> {
         tools = tools.push(modes);
     }
     if projection == Some(ProjectionKind::Allocation) {
+        // Reserve this slot even when idle: changing feedback must never resize
+        // the measured canvas and invalidate a held gesture. Its identity is
+        // independent of status length, target geometry and the diagram zoom.
+        let destination = app
+            .allocation_drag
+            .feedback
+            .as_ref()
+            .map(|feedback| feedback.destination_identity())
+            .unwrap_or_else(|| "None · drag work to choose".into());
+        tools = tools.push(
+            container(tooltip(
+                text(format!("Destination: {}", short(&destination, 28)))
+                    .size(13)
+                    .wrapping(widget::text::Wrapping::None),
+                container(text(destination).size(13))
+                    .padding(10)
+                    .max_width(420)
+                    .style(style::card),
+                tooltip::Position::Top,
+            ))
+            .id("allocation-destination")
+            .height(26)
+            .width(Fill)
+            .clip(true),
+        );
         tools = tools.push(
             row![
                 action(
@@ -561,7 +586,7 @@ fn diagram(app: &App) -> View<'_, Message> {
             "Right-click for actions · drag to arrange · scroll to zoom"
         };
         // Status is outside the measured canvas. Clipping prevents long text
-        // from painting over work headers or frozen target labels below it.
+        // from painting over work headers or the dedicated destination slot.
         tools = tools.push(container(label(hint)).height(30).width(Fill).clip(true));
     }
     column![container(tools).padding(14), canvas].into()