diff --git a/crates/oa-desktop/src/app/allocation_drag_tests.rs b/crates/oa-desktop/src/app/allocation_drag_tests.rs
index 58b5a391..490429f4 100644
--- a/crates/oa-desktop/src/app/allocation_drag_tests.rs
+++ b/crates/oa-desktop/src/app/allocation_drag_tests.rs
@@ -1310,6 +1310,250 @@ fn outgoing_boundary_drop_clears_source_without_changing_other_placements() {
     }
 }
 
+#[test]
+fn outgoing_clearance_collision_refuses_release_without_source_or_history_mutation() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        let mut f = outgoing_fixture(layer);
+        let mut project = f.app.project().clone();
+        let obstacle = project
+            .add_element(
+                project.elements[&f.work].kind(),
+                layer,
+                "Unrelated work",
+                None,
+            )
+            .unwrap();
+        let obstacle_node = project.place(f.diagram, obstacle, xy(240., 190.));
+        replace(&mut f, project);
+        // A refused release must preserve an existing redo branch, too.
+        let _ = f.app.update(Message::Command(Command::Rename(
+            f.work,
+            "Temporary".into(),
+        )));
+        let _ = f.app.update(Message::Undo);
+        let before = f.app.project().clone();
+        let source = f.app.document.bundle().clone();
+        let snapshot = f.app.document.snapshot();
+        let revision = f.app.document.revision();
+        let from = screen(xy(660., 225.));
+        let to = screen(xy(490., 225.));
+        let mut events = batch(&f.app, from, to);
+        let release = events.pop().unwrap();
+        send(&mut f.app, events);
+
+        let active = f.app.allocation_drag.active.as_ref().unwrap();
+        let p = &active.press;
+        let frozen = active.frozen.as_ref().unwrap();
+        let owner = frozen.targets.iter().find(|t| t.element == f.a).unwrap();
+        assert_eq!(p.start, from);
+        assert!(contains(owner.region, p.stamp.world(from)));
+        assert!(p.stamp.world(to).x < owner.region.x);
+        assert_eq!(
+            frozen.resolve(p.stamp, Some(to), false),
+            Hit::Destination(plan::Destination::OutsidePerformers, None),
+            "The pointer must reach empty canvas, not be occluded by the obstacle"
+        );
+        let candidate = active
+            .cache
+            .iter()
+            .find(|(destination, _)| *destination == plan::Destination::OutsidePerformers)
+            .unwrap()
+            .1
+            .as_ref()
+            .unwrap();
+        let affected = match &active.prepared {
+            Prepared::Singleton(scope) => &scope.placements,
+            Prepared::Assignment(scope) => scope.affected(),
+            _ => panic!("expected assignment gesture"),
+        };
+        let requested = xy(370., 190.);
+        let presentation = plan::PresentationContext {
+            viewport: p.stamp.viewport(),
+            zoom: p.stamp.zoom,
+            target: None,
+        };
+        assert!(matches!(
+            candidate.place(requested, presentation),
+            Err(plan::Refusal::LayoutRequired(_))
+        ));
+        let proposed = clearance::requests(
+            (f.app.project(), f.app.document.view_index()),
+            (candidate.project(), candidate.index()),
+            f.diagram,
+            affected,
+            f.node,
+            requested,
+            (p.stamp.world(from), p.stamp.world(to)),
+        );
+        assert_eq!(
+            proposed.len(),
+            1,
+            "a genuine left crossing must propose clearance"
+        );
+        assert!(proposed[0].x < requested.x);
+        let work = &before.diagrams[&f.diagram].nodes[&f.node];
+        let obstacle = &before.diagrams[&f.diagram].nodes[&obstacle_node];
+        assert!(obstacle.position.x + obstacle.size.width < 490.);
+        assert!(proposed[0].x + work.size.width <= owner.region.x - 10.);
+        assert!(proposed[0].x < obstacle.position.x + obstacle.size.width);
+        assert!(obstacle.position.x < proposed[0].x + work.size.width);
+        assert_eq!(proposed[0].y, obstacle.position.y);
+        assert!(matches!(
+            candidate.place(proposed[0], presentation),
+            Err(plan::Refusal::LayoutRequired(message)) if message.contains("overlapping cards")
+        ));
+        let feedback = f.app.allocation_drag.feedback.as_ref().unwrap();
+        assert!(feedback.refused, "{}", feedback.text);
+        assert!(feedback.ghost_delta.is_some());
+        assert!(f.app.allocation_drag.preview.is_none());
+        assert_eq!(f.app.project(), &before);
+        assert_eq!(f.app.document.bundle(), &source);
+        assert!(Arc::ptr_eq(&snapshot, &f.app.document.snapshot()));
+        let _ = f.app.update(release);
+        assert!(
+            f.app.status.contains("overlapping cards"),
+            "{}",
+            f.app.status
+        );
+        assert!(f.app.allocation_drag.active.is_none());
+        assert!(f.app.allocation_drag.preview.is_none());
+        assert_eq!(f.app.project(), &before);
+        assert_eq!(f.app.document.bundle(), &source);
+        assert_eq!(f.app.document.revision(), revision);
+        assert!(Arc::ptr_eq(&snapshot, &f.app.document.snapshot()));
+        assert!(!f.app.document.can_undo());
+        assert!(f.app.document.can_redo());
+    }
+}
+
+#[test]
+fn outgoing_clearance_preserves_source_enclosure_and_allocated_sibling() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        let mut f = outgoing_fixture(layer);
+        let mut project = f.app.project().clone();
+        let sibling = project
+            .add_element(
+                project.elements[&f.work].kind(),
+                layer,
+                "Remaining work",
+                None,
+            )
+            .unwrap();
+        let sibling_node = project.place(f.diagram, sibling, xy(540., 450.));
+        let allocation = project.relate(
+            RelationKind::Allocation,
+            "Keep responsibility",
+            f.a,
+            sibling,
+        );
+        replace(&mut f, project);
+        let before = f.app.project().clone();
+        let source = f.app.document.bundle().clone();
+        let view = projection::project_view(&before, f.diagram);
+        let owner = view.nodes.iter().find(|n| n.element == f.a).unwrap();
+        let bottom = owner.position.y + owner.size.height;
+        let stored_owner = &before.diagrams[&f.diagram].nodes[&owner.id];
+        assert!(
+            bottom > stored_owner.position.y + stored_owner.size.height,
+            "The retained sibling must enlarge the projected source enclosure"
+        );
+        let from = screen(xy(660., 225.));
+        let to = screen(xy(660., bottom + 1.));
+        let mut events = batch(&f.app, from, to);
+        let release = events.pop().unwrap();
+        send(&mut f.app, events);
+        let active = f.app.allocation_drag.active.as_ref().unwrap();
+        let p = &active.press;
+        let frozen = active.frozen.as_ref().unwrap();
+        let target = frozen.targets.iter().find(|t| t.element == f.a).unwrap();
+        assert_eq!(p.start, from);
+        assert!(contains(target.region, p.stamp.world(from)));
+        assert!(p.stamp.world(to).y >= target.region.y + target.region.height);
+        assert_eq!(
+            frozen.resolve(p.stamp, Some(to), false),
+            Hit::Destination(plan::Destination::OutsidePerformers, None)
+        );
+        let preview = f.app.allocation_drag.preview.as_ref().expect(&f.app.status);
+        assert!(!f.app.allocation_drag.feedback.as_ref().unwrap().refused);
+        let requested = xy(540., 190. + to.y - from.y);
+        assert!(matches!(
+            preview.candidate.place(
+                requested,
+                plan::PresentationContext {
+                    viewport: p.stamp.viewport(),
+                    zoom: p.stamp.zoom,
+                    target: None,
+                }
+            ),
+            Err(plan::Refusal::LayoutRequired(_))
+        ));
+        let moved = &preview.placement.diagram.nodes[&f.node];
+        assert_eq!(moved.position.x, 540.);
+        assert!(moved.position.y >= bottom + 10.);
+        assert!(moved.position.y > requested.y);
+        assert_eq!(
+            preview
+                .placement
+                .view
+                .nodes
+                .iter()
+                .find(|n| n.id == owner.id)
+                .unwrap(),
+            owner
+        );
+        let remaining = preview
+            .placement
+            .view
+            .nodes
+            .iter()
+            .find(|n| n.id == sibling_node)
+            .unwrap();
+        assert_eq!(remaining.visual_parent, Some(owner.id));
+        assert_eq!(
+            remaining.position,
+            before.diagrams[&f.diagram].nodes[&sibling_node].position
+        );
+        assert_eq!(
+            &preview.project().relations[&allocation],
+            &before.relations[&allocation]
+        );
+        for (id, node) in &before.diagrams[&f.diagram].nodes {
+            if *id != f.node {
+                assert_eq!(&preview.placement.diagram.nodes[id], node);
+            }
+        }
+        let mut expected = preview.project().clone();
+        expected
+            .diagrams
+            .insert(f.diagram, preview.placement.diagram.clone());
+        assert_eq!(f.app.project(), &before);
+        assert_eq!(f.app.document.bundle(), &source);
+        let _ = f.app.update(release);
+        assert_eq!(f.app.project(), &expected, "{}", f.app.status);
+        assert_eq!(f.app.document.revision(), 1);
+        assert_eq!(
+            validation::effective_performer(f.app.project(), f.work),
+            None
+        );
+        assert_eq!(
+            validation::effective_performer(f.app.project(), sibling),
+            Some(f.a)
+        );
+        assert_eq!(
+            &f.app.project().relations[&allocation],
+            &before.relations[&allocation]
+        );
+        let after = f.app.document.bundle().clone();
+        let _ = f.app.update(Message::Undo);
+        assert_eq!(f.app.project(), &before);
+        assert_eq!(f.app.document.bundle(), &source);
+        assert!(!f.app.document.can_undo());
+        let _ = f.app.update(Message::Redo);
+        assert_eq!(f.app.project(), &expected);
+        assert_eq!(f.app.document.bundle(), &after);
+    }
+}
+
 #[test]
 fn refused_motion_retains_last_scene_but_release_never_commits_it() {
     let mut f = outgoing_fixture(Layer::Sa);