diff --git a/crates/oa-desktop/src/allocation_drag.rs b/crates/oa-desktop/src/allocation_drag.rs
index a903c682..66cdbb6d 100644
--- a/crates/oa-desktop/src/allocation_drag.rs
+++ b/crates/oa-desktop/src/allocation_drag.rs
@@ -13,6 +13,11 @@ use oa_core::{
 };
 use std::collections::{BTreeMap, BTreeSet};
 
+// The pure planner is verified before its App gesture adapter is connected.
+#[allow(dead_code)]
+#[path = "allocation_drag/arrange.rs"]
+pub mod arrange;
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Destination {
     LayoutOnly,
@@ -76,6 +81,11 @@ pub enum Refusal {
 
 pub fn capture(p: &Project, diagram: Id, work: Id, placement: Id) -> Result<Scope, Refusal> {
     validate_candidate(p).map_err(|e| Refusal::InvalidCandidate(e.to_string()))?;
+    capture_validated(p, diagram, work, placement)
+}
+
+/// Collect work facts after the caller's single complete Project validation.
+fn capture_validated(p: &Project, diagram: Id, work: Id, placement: Id) -> Result<Scope, Refusal> {
     let d = p.diagrams.get(&diagram).ok_or(Refusal::StaleScope)?;
     let root = p.elements.get(&work).ok_or(Refusal::StaleScope)?;
     if !root.kind().is_work()
diff --git a/crates/oa-desktop/src/allocation_drag/arrange.rs b/crates/oa-desktop/src/allocation_drag/arrange.rs
new file mode 100644
index 00000000..39d3d444
--- /dev/null
+++ b/crates/oa-desktop/src/allocation_drag/arrange.rs
@@ -0,0 +1,342 @@
+//! Explicit, semantics-preserving arrangement of one or more Allocation cards.
+//!
+//! The App must admit the entire original typed selection before converting it
+//! to placement/element identities. These values do not grant input authority.
+use super::*;
+
+#[derive(Debug)]
+pub struct Plan {
+    accepted: Project,
+    diagram: Id,
+    selected: BTreeMap<Id, Id>,
+    anchor: Id,
+    placements: BTreeMap<Id, NodePlacement>,
+    expanded_ids: BTreeSet<Id>,
+    index: ViewIndex,
+    before_visible: ProjectedView,
+    before_expanded: ProjectedView,
+}
+
+impl Plan {
+    pub fn project(&self) -> &Project {
+        &self.accepted
+    }
+
+    pub fn index(&self) -> &ViewIndex {
+        &self.index
+    }
+
+    pub fn affected(&self) -> &BTreeMap<Id, NodePlacement> {
+        &self.placements
+    }
+
+    pub fn selected(&self) -> &BTreeMap<Id, Id> {
+        &self.selected
+    }
+
+    pub fn anchor(&self) -> Id {
+        self.anchor
+    }
+
+    pub fn diagram(&self) -> &Diagram {
+        &self.accepted.diagrams[&self.diagram]
+    }
+}
+
+/// Capture every original placement identity before normalizing semantic roots.
+/// Document/revision/selection-generation and clean-owner guards belong to App.
+pub fn capture(
+    p: &Project,
+    diagram: Id,
+    selected: &BTreeMap<Id, Id>,
+    anchor: Id,
+) -> Result<Plan, Refusal> {
+    validate_candidate(p).map_err(|e| Refusal::InvalidCandidate(e.to_string()))?;
+    let d = p.diagrams.get(&diagram).ok_or(Refusal::StaleScope)?;
+    if d.projection != ProjectionKind::Allocation
+        || selected.is_empty()
+        || !selected.contains_key(&anchor)
+    {
+        return Err(Refusal::Ineligible(
+            "Arrange requires selected placements and a selected anchor in an Allocation view."
+                .into(),
+        ));
+    }
+    let index = ViewIndex::new(p);
+    let before_visible = projection::project_diagram_with_index(p, d, &index);
+    let visible: BTreeMap<_, _> = before_visible
+        .nodes
+        .iter()
+        .map(|n| (n.id, n.element))
+        .collect();
+    let mut work = BTreeMap::new();
+    let mut performers = Vec::new();
+    for (placement, element) in selected {
+        let node = d.nodes.get(placement).ok_or(Refusal::StaleScope)?;
+        let record = p.elements.get(element).ok_or(Refusal::StaleScope)?;
+        if node.element != *element || visible.get(placement) != Some(element) {
+            return Err(Refusal::StaleScope);
+        }
+        if record.layer() != d.layer || !(record.kind().is_work() || record.kind().is_performer()) {
+            return Err(Refusal::Ineligible(
+                "Arrange requires only activities, functions or performers in this layer.".into(),
+            ));
+        }
+        if record.kind().is_work() {
+            work.insert(*element, *placement);
+        } else {
+            performers.push(*placement);
+        }
+    }
+
+    let mut placements = BTreeMap::new();
+    for (element, placement) in &work {
+        let root = &p.elements[element];
+        let mut ancestor = root.parent;
+        let mut covered = false;
+        let mut seen = BTreeSet::new();
+        while let Some(id) = ancestor {
+            if !seen.insert(id) {
+                return Err(Refusal::StaleScope);
+            }
+            let parent = p.elements.get(&id).ok_or(Refusal::StaleScope)?;
+            if parent.kind() != root.kind() {
+                break;
+            }
+            if work.contains_key(&id) {
+                covered = true;
+                break;
+            }
+            ancestor = parent.parent;
+        }
+        if !covered {
+            placements.extend(capture_validated(p, diagram, *element, *placement)?.placements);
+        }
+    }
+    for performer in performers {
+        for id in
+            std::iter::once(performer).chain(projection::descendant_nodes(p, diagram, performer))
+        {
+            placements.insert(id, d.nodes.get(&id).ok_or(Refusal::StaleScope)?.clone());
+        }
+    }
+
+    // Geometry never changes visual ancestry in Arrange. Recover the complete
+    // ancestry once, including hidden nodes. This all-unfolded projection is
+    // used only for identity lookup, never as a collision-admission scene.
+    let mut all_unfolded = d.clone();
+    for node in all_unfolded.nodes.values_mut() {
+        node.collapsed = false;
+    }
+    let all_view = projection::project_diagram_with_index(p, &all_unfolded, &index);
+    let ancestry = ancestors(&all_view);
+    let mut expanded_ids: BTreeSet<_> = placements.keys().copied().collect();
+    for id in placements.keys() {
+        expanded_ids.extend(ancestry.get(id).ok_or(Refusal::StaleScope)?.iter().copied());
+    }
+    let before_expanded = diagnostic(p, d, &expanded_ids, &index);
+    Ok(Plan {
+        accepted: p.clone(),
+        diagram,
+        selected: selected.clone(),
+        anchor,
+        placements,
+        expanded_ids,
+        index,
+        before_visible,
+        before_expanded,
+    })
+}
+
+fn diagnostic(
+    project: &Project,
+    diagram: &Diagram,
+    expanded_ids: &BTreeSet<Id>,
+    index: &ViewIndex,
+) -> ProjectedView {
+    let mut expanded = diagram.clone();
+    for id in expanded_ids {
+        if let Some(node) = expanded.nodes.get_mut(id) {
+            node.collapsed = false;
+        }
+    }
+    projection::project_diagram_with_index(project, &expanded, index)
+}
+
+/// Snap the captured anchor once; preview the complete union without cloning or
+/// validating a Project, rebuilding its semantic index, or expanding scope.
+pub fn place(
+    plan: &Plan,
+    requested: Position,
+    presentation: PresentationContext,
+) -> Result<PlacementPlan, Refusal> {
+    if presentation.target.is_some() {
+        return Err(Refusal::Ineligible(
+            "Arrange only has no performer destination.".into(),
+        ));
+    }
+    if !requested.x.is_finite()
+        || !requested.y.is_finite()
+        || !presentation.viewport.valid()
+        || !presentation.zoom.is_finite()
+        || presentation.zoom <= 0.
+    {
+        return Err(Refusal::LayoutRequired(
+            "Make room or adjust the view, then drag again.".into(),
+        ));
+    }
+    let anchor = &plan.placements[&plan.anchor];
+    let delta = Position {
+        x: (requested.x / 10.).round() * 10. - anchor.position.x,
+        y: (requested.y / 10.).round() * 10. - anchor.position.y,
+    };
+    let mut diagram = plan.diagram().clone();
+    let mut commands = Vec::new();
+    let mut deltas = BTreeMap::new();
+    for (id, original) in &plan.placements {
+        let node = diagram.nodes.get_mut(id).ok_or(Refusal::StaleScope)?;
+        node.position = Position {
+            x: original.position.x + delta.x,
+            y: original.position.y + delta.y,
+        };
+        if !(Rect {
+            position: node.position,
+            size: node.size,
+        })
+        .valid()
+        {
+            return Err(Refusal::InvalidCandidate(
+                "Moved coordinates exceed the model bounds.".into(),
+            ));
+        }
+        deltas.insert(*id, delta);
+        if node != original {
+            commands.push(Command::EditNode {
+                diagram: diagram.id,
+                original: *id,
+                node: node.clone(),
+            });
+        }
+    }
+    for route in projection::translated_routes(&plan.accepted, plan.diagram(), &deltas) {
+        if route.waypoints.iter().any(|point| {
+            !point.x.is_finite()
+                || !point.y.is_finite()
+                || point.x.abs() > MAX_COORDINATE
+                || point.y.abs() > MAX_COORDINATE
+        }) {
+            return Err(Refusal::InvalidCandidate(
+                "Moved route exceeds the model bounds.".into(),
+            ));
+        }
+        let stored = diagram
+            .routes
+            .iter_mut()
+            .find(|stored| stored.edge == route.edge)
+            .ok_or(Refusal::StaleScope)?;
+        *stored = route.clone();
+        commands.push(Command::SetEdgeRoute {
+            diagram: diagram.id,
+            route,
+        });
+    }
+    let view = projection::project_diagram_with_index(&plan.accepted, &diagram, &plan.index);
+    let expanded = diagnostic(&plan.accepted, &diagram, &plan.expanded_ids, &plan.index);
+    if view.nodes.iter().chain(&expanded.nodes).any(|node| {
+        !(Rect {
+            position: node.position,
+            size: node.size,
+        })
+        .valid()
+    }) {
+        return Err(Refusal::InvalidCandidate(
+            "The projected enclosure exceeds the model bounds.".into(),
+        ));
+    }
+    let before: BTreeMap<_, _> = plan
+        .before_expanded
+        .nodes
+        .iter()
+        .map(|n| (n.id, n))
+        .collect();
+    let after: BTreeMap<_, _> = expanded.nodes.iter().map(|n| (n.id, n)).collect();
+    for id in plan.placements.keys() {
+        let old = before.get(id).ok_or(Refusal::StaleScope)?;
+        let new = after.get(id).ok_or(Refusal::StaleScope)?;
+        if (new.position.x - old.position.x - delta.x).abs() > 0.01
+            || (new.position.y - old.position.y - delta.y).abs() > 0.01
+            || (new.size.width - old.size.width).abs() > 0.01
+            || (new.size.height - old.size.height).abs() > 0.01
+        {
+            return Err(Refusal::LayoutRequired(
+                "This selection requires an explicit layout; its footprint cannot be translated unchanged."
+                    .into(),
+            ));
+        }
+    }
+    if overlaps(&plan.before_visible, &view) || overlaps(&plan.before_expanded, &expanded) {
+        return Err(Refusal::LayoutRequired(
+            "Make room before arranging: the candidate would introduce or enlarge overlapping cards."
+                .into(),
+        ));
+    }
+    for (id, element) in &plan.selected {
+        let selected = view
+            .nodes
+            .iter()
+            .find(|node| node.id == *id && node.element == *element)
+            .ok_or_else(|| Refusal::LayoutRequired("A selected header would be hidden.".into()))?;
+        let header = Rect {
+            position: selected.position,
+            size: Size {
+                width: selected.size.width,
+                height: selected.size.height.min(62.),
+            },
+        };
+        if !presentation.viewport.contains(header) {
+            return Err(Refusal::LayoutRequired(
+                "Make room or adjust the view, then drag again.".into(),
+            ));
+        }
+    }
+    Ok(PlacementPlan {
+        diagram,
+        view,
+        delta,
+        unfolded: None,
+        requested,
+        presentation,
+        commands,
+    })
+}
+
+/// Recompute the candidate and compare the complete expected Project before the
+/// caller performs one source-admitted transaction. None means no history entry.
+pub fn finish(
+    plan: &Plan,
+    live: &Project,
+    placement: &PlacementPlan,
+) -> Result<Option<Command>, Refusal> {
+    if live != &plan.accepted {
+        return Err(Refusal::StaleScope);
+    }
+    let checked = place(plan, placement.requested, placement.presentation)?;
+    if checked.diagram != placement.diagram
+        || checked.view != placement.view
+        || checked.delta != placement.delta
+        || checked.unfolded != placement.unfolded
+        || checked.commands != placement.commands
+    {
+        return Err(Refusal::StaleScope);
+    }
+    let mut expected = plan.accepted.clone();
+    expected
+        .diagrams
+        .insert(checked.diagram.id, checked.diagram);
+    let command = Command::Batch(checked.commands);
+    let actual = prepare_command(live, &command)
+        .map_err(|e| Refusal::InvalidCandidate(e.to_string()))?
+        .project;
+    exact_project(&expected, &actual)?;
+    Ok((actual != *live).then_some(command))
+}
diff --git a/crates/oa-desktop/src/allocation_drag/arrange_tests.rs b/crates/oa-desktop/src/allocation_drag/arrange_tests.rs
new file mode 100644
index 00000000..f3c86973
--- /dev/null
+++ b/crates/oa-desktop/src/allocation_drag/arrange_tests.rs
@@ -0,0 +1,443 @@
+use super::*;
+
+struct Distributed {
+    f: Fixture,
+    a: Id,
+    b: Id,
+    x: Id,
+    y: Id,
+    internal: Id,
+}
+
+fn distributed(layer: Layer, folded: bool) -> Distributed {
+    let mut f = fixture(layer);
+    let kind = f.p.elements[&f.w].kind();
+    let x = f.p.add_element(kind, layer, "X", Some(f.w)).unwrap();
+    let y = f.p.add_element(kind, layer, "Y", Some(f.w)).unwrap();
+    let outside = f.p.add_element(kind, layer, "Outside", None).unwrap();
+    let xn = f.p.place(f.d, x, xy(140., 200.));
+    let yn = f.p.place(f.d, y, xy(940., 200.));
+    f.p.place(f.d, outside, xy(1800., 800.));
+    f.p.relate(RelationKind::Allocation, "A owns X", f.a, x);
+    f.p.relate(RelationKind::Allocation, "B owns Y", f.b, y);
+    let exchange = match layer {
+        Layer::Oa => RelationKind::Interaction,
+        Layer::Sa => RelationKind::FunctionalExchange,
+    };
+    let internal = f.p.relate(exchange, "X to Y", x, y);
+    let external = f.p.relate(exchange, "Y to Outside", y, outside);
+    let d = f.p.diagrams.get_mut(&f.d).unwrap();
+    let a = d.nodes.values().find(|n| n.element == f.a).unwrap().id;
+    let b = d.nodes.values().find(|n| n.element == f.b).unwrap().id;
+    d.nodes.get_mut(&a).unwrap().collapsed = folded;
+    d.nodes.get_mut(&f.n).unwrap().position = xy(100., 800.);
+    d.routes = vec![route(internal), route(external)];
+    validate_candidate(&f.p).unwrap();
+    Distributed {
+        f,
+        a,
+        b,
+        x: xn,
+        y: yn,
+        internal,
+    }
+}
+
+fn identities(m: &Distributed, ids: &[Id]) -> BTreeMap<Id, Id> {
+    ids.iter()
+        .map(|id| (*id, m.f.p.diagrams[&m.f.d].nodes[id].element))
+        .collect()
+}
+
+fn expected(m: &Distributed, include_a: bool) -> Project {
+    let mut p = m.f.p.clone();
+    let d = p.diagrams.get_mut(&m.f.d).unwrap();
+    for (id, position) in [
+        (m.f.n, xy(500., 800.)),
+        (m.x, xy(540., 200.)),
+        (m.y, xy(1340., 200.)),
+    ] {
+        d.nodes.get_mut(&id).unwrap().position = position;
+    }
+    if include_a {
+        d.nodes.get_mut(&m.a).unwrap().position = xy(500., 100.);
+    }
+    d.routes
+        .iter_mut()
+        .find(|r| r.edge == m.internal)
+        .unwrap()
+        .waypoints = vec![xy(820., 400.), xy(820., 550.)];
+    p
+}
+
+#[test]
+fn explicit_arrange_distributed_oa_sa_exact_scope_routes_source_history_and_anchor() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        for folded in [false, true] {
+            for include_a in [false, true] {
+                let m = distributed(layer, folded);
+                let members = if include_a {
+                    vec![m.f.n, m.a]
+                } else {
+                    vec![m.f.n]
+                };
+                let selected = identities(&m, &members);
+                for anchor in selected.keys().copied() {
+                    let plan = arrange::capture(&m.f.p, m.f.d, &selected, anchor).unwrap();
+                    assert_eq!(plan.selected(), &selected);
+                    let mut affected = BTreeSet::from([m.f.n, m.x, m.y]);
+                    if include_a {
+                        affected.insert(m.a);
+                    }
+                    assert_eq!(
+                        plan.affected().keys().copied().collect::<BTreeSet<_>>(),
+                        affected
+                    );
+                    let requested = if anchor == m.a {
+                        xy(503., 102.)
+                    } else {
+                        xy(503., 802.)
+                    };
+                    let placed =
+                        arrange::place(&plan, requested, presentation(&m.f.p, m.f.d, None))
+                            .unwrap();
+                    assert_eq!(placed.delta, xy(400., 0.));
+                    assert_eq!(placed.unfolded, None);
+                    let command = arrange::finish(&plan, &m.f.p, &placed).unwrap().unwrap();
+                    assert_eq!(roundtrip(&m.f.p, command), expected(&m, include_a));
+                    // Explicit Arrange does not widen ordinary distributed assignment.
+                    assert!(matches!(
+                        plan_semantics(
+                            &m.f.p,
+                            &scope(&m.f),
+                            Destination::Performer(m.f.a),
+                            &BTreeMap::new()
+                        ),
+                        Err(Refusal::MixedLayoutRequired)
+                    ));
+                }
+            }
+        }
+    }
+}
+
+#[test]
+fn explicit_arrange_performer_closure_does_not_acquire_incidental_semantic_root() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        let m = distributed(layer, true);
+        let selected = identities(&m, &[m.a]);
+        let plan = arrange::capture(&m.f.p, m.f.d, &selected, m.a).unwrap();
+        assert_eq!(
+            plan.affected().keys().copied().collect::<BTreeSet<_>>(),
+            BTreeSet::from([m.a, m.x])
+        );
+        let placed =
+            arrange::place(&plan, xy(500., 100.), presentation(&m.f.p, m.f.d, None)).unwrap();
+        let mut expected = m.f.p.clone();
+        let d = expected.diagrams.get_mut(&m.f.d).unwrap();
+        d.nodes.get_mut(&m.a).unwrap().position = xy(500., 100.);
+        d.nodes.get_mut(&m.x).unwrap().position = xy(540., 200.);
+        // X-to-Y is now one-ended; all saved pins remain byte-for-byte unchanged.
+        assert_eq!(
+            roundtrip(
+                &m.f.p,
+                arrange::finish(&plan, &m.f.p, &placed).unwrap().unwrap()
+            ),
+            expected
+        );
+    }
+}
+
+#[test]
+fn explicit_arrange_validates_all_original_members_before_normalizing() {
+    let mut m = distributed(Layer::Oa, false);
+    let selected = identities(&m, &[m.f.n, m.x]);
+    let plan = arrange::capture(&m.f.p, m.f.d, &selected, m.x).unwrap();
+    assert_eq!(plan.selected(), &selected);
+    assert_eq!(plan.affected().len(), 3);
+    let placed = arrange::place(&plan, xy(540., 200.), presentation(&m.f.p, m.f.d, None)).unwrap();
+    assert_eq!(
+        roundtrip(
+            &m.f.p,
+            arrange::finish(&plan, &m.f.p, &placed).unwrap().unwrap()
+        ),
+        expected(&m, false)
+    );
+    let mut stale = selected.clone();
+    stale.insert(m.x, m.f.w);
+    assert!(arrange::capture(&m.f.p, m.f.d, &stale, m.f.n).is_err());
+    m.f.p
+        .diagrams
+        .get_mut(&m.f.d)
+        .unwrap()
+        .nodes
+        .get_mut(&m.a)
+        .unwrap()
+        .collapsed = true;
+    assert!(
+        arrange::capture(&m.f.p, m.f.d, &selected, m.f.n).is_err(),
+        "covered selected X is hidden and cannot disappear in normalization"
+    );
+    assert!(arrange::capture(&m.f.p, m.f.d, &BTreeMap::new(), m.f.n).is_err());
+    assert!(arrange::capture(&m.f.p, m.f.d, &identities(&m, &[m.f.n]), m.a).is_err());
+    assert!(arrange::capture(&m.f.p, m.f.second, &identities(&m, &[m.f.n]), m.f.n).is_err());
+    let foreign = Id::new_v4();
+    assert!(
+        arrange::capture(
+            &m.f.p,
+            m.f.d,
+            &BTreeMap::from([(m.f.n, m.f.w), (foreign, m.f.w)]),
+            m.f.n
+        )
+        .is_err()
+    );
+    m.f.p.diagrams.get_mut(&m.f.d).unwrap().projection = ProjectionKind::Overview;
+    assert!(arrange::capture(&m.f.p, m.f.d, &identities(&m, &[m.f.n]), m.f.n).is_err());
+}
+
+#[test]
+fn explicit_arrange_simultaneous_roots_may_enter_each_others_vacated_bounds() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        let mut f = fixture(layer);
+        let kind = f.p.elements[&f.w].kind();
+        let y = f.p.add_element(kind, layer, "Second root", None).unwrap();
+        let yn = f.p.place(f.d, y, xy(400., 500.));
+        let relation = f.p.relate(
+            if layer == Layer::Oa {
+                RelationKind::Interaction
+            } else {
+                RelationKind::FunctionalExchange
+            },
+            "Between roots",
+            f.w,
+            y,
+        );
+        f.p.diagrams.get_mut(&f.d).unwrap().routes = vec![route(relation)];
+        let context = presentation(&f.p, f.d, None);
+        let single = arrange::capture(&f.p, f.d, &BTreeMap::from([(f.n, f.w)]), f.n).unwrap();
+        assert!(
+            arrange::place(&single, xy(400., 500.), context).is_err(),
+            "singleton would collide with stationary Y"
+        );
+        let plan =
+            arrange::capture(&f.p, f.d, &BTreeMap::from([(f.n, f.w), (yn, y)]), f.n).unwrap();
+        let placed = arrange::place(&plan, xy(400., 500.), context).unwrap();
+        let mut expected = f.p.clone();
+        let d = expected.diagrams.get_mut(&f.d).unwrap();
+        d.nodes.get_mut(&f.n).unwrap().position = xy(400., 500.);
+        d.nodes.get_mut(&yn).unwrap().position = xy(700., 500.);
+        d.routes[0].waypoints = vec![xy(720., 400.), xy(720., 550.)];
+        assert_eq!(
+            roundtrip(
+                &f.p,
+                arrange::finish(&plan, &f.p, &placed).unwrap().unwrap()
+            ),
+            expected
+        );
+    }
+}
+
+#[test]
+fn explicit_arrange_preserves_roles_and_does_not_invent_unplaced_descendants() {
+    let mut f = fixture(Layer::Oa);
+    let a = f.a;
+    role(&mut f, Some(a));
+    f.p.diagrams
+        .get_mut(&f.d)
+        .unwrap()
+        .nodes
+        .get_mut(&f.n)
+        .unwrap()
+        .position = xy(150., 200.);
+    let plan = arrange::capture(&f.p, f.d, &BTreeMap::from([(f.n, f.w)]), f.n).unwrap();
+    let placed = arrange::place(&plan, xy(160., 210.), presentation(&f.p, f.d, None)).unwrap();
+    let mut role_expected = f.p.clone();
+    role_expected
+        .diagrams
+        .get_mut(&f.d)
+        .unwrap()
+        .nodes
+        .get_mut(&f.n)
+        .unwrap()
+        .position = xy(160., 210.);
+    assert_eq!(
+        roundtrip(
+            &f.p,
+            arrange::finish(&plan, &f.p, &placed).unwrap().unwrap()
+        ),
+        role_expected
+    );
+    for layer in [Layer::Oa, Layer::Sa] {
+        let mut m = distributed(layer, true);
+        let kind = m.f.p.elements[&m.f.w].kind();
+        m.f.p
+            .add_element(kind, layer, "Unplaced leaf", Some(m.f.w))
+            .unwrap();
+        let plan = arrange::capture(&m.f.p, m.f.d, &identities(&m, &[m.f.n]), m.f.n).unwrap();
+        assert_eq!(plan.affected().len(), 3);
+        let placed =
+            arrange::place(&plan, xy(500., 800.), presentation(&m.f.p, m.f.d, None)).unwrap();
+        assert_eq!(
+            roundtrip(
+                &m.f.p,
+                arrange::finish(&plan, &m.f.p, &placed).unwrap().unwrap()
+            ),
+            expected(&m, false)
+        );
+    }
+}
+
+#[test]
+fn explicit_arrange_detects_hidden_moved_child_and_stationary_enclosure_growth() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        for hidden in [false, true] {
+            let mut m = distributed(layer, hidden);
+            let kind = m.f.p.elements[&m.f.w].kind();
+            let z = m.f.p.add_element(kind, layer, "Obstacle", None).unwrap();
+            let zn = m.f.p.place(
+                m.f.d,
+                z,
+                if hidden {
+                    xy(550., 230.)
+                } else {
+                    xy(1200., 100.)
+                },
+            );
+            // The independent candidate differs only by literal admitted edits.
+            // Establish which geometric case the real planner must reject.
+            let candidate = expected(&m, true);
+            let before = projection::project_view(&m.f.p, m.f.d);
+            let after = projection::project_view(&candidate, m.f.d);
+            let find =
+                |view: &ProjectedView, id| view.nodes.iter().find(|n| n.id == id).unwrap().clone();
+            if hidden {
+                assert!(!overlaps(&before, &after));
+                assert!(!after.nodes.iter().any(|n| n.id == m.x));
+                let mut diagnostic = candidate.diagrams[&m.f.d].clone();
+                diagnostic.nodes.get_mut(&m.a).unwrap().collapsed = false;
+                let expanded = projection::project_diagram(&candidate, &diagnostic);
+                assert_eq!(
+                    overlap(&find(&expanded, m.x), &find(&expanded, zn)),
+                    if layer == Layer::Oa { 13696. } else { 20116. }
+                );
+            } else {
+                assert_eq!(overlap(&find(&before, m.b), &find(&before, zn)), 0.);
+                assert_eq!(overlap(&find(&after, m.b), &find(&after, zn)), 21056.);
+                for id in [m.a, m.f.n, m.x, m.y] {
+                    assert_eq!(overlap(&find(&after, id), &find(&after, zn)), 0.);
+                }
+                assert_eq!(
+                    candidate.diagrams[&m.f.d].nodes[&m.b],
+                    m.f.p.diagrams[&m.f.d].nodes[&m.b]
+                );
+            }
+            let plan =
+                arrange::capture(&m.f.p, m.f.d, &identities(&m, &[m.a, m.f.n]), m.f.n).unwrap();
+            assert!(matches!(
+                arrange::place(&plan, xy(500., 800.), presentation(&m.f.p, m.f.d, None)),
+                Err(Refusal::LayoutRequired(_))
+            ));
+        }
+    }
+}
+
+#[test]
+fn explicit_arrange_preserves_existing_overlap_but_refuses_its_growth() {
+    let mut f = fixture(Layer::Oa);
+    let y =
+        f.p.add_element(Kind::Activity, Layer::Oa, "Existing overlap", None)
+            .unwrap();
+    let yn = f.p.place(f.d, y, xy(250., 500.));
+    let context = presentation(&f.p, f.d, None);
+    let single = arrange::capture(&f.p, f.d, &BTreeMap::from([(f.n, f.w)]), f.n).unwrap();
+    assert!(arrange::place(&single, xy(110., 500.), context).is_err());
+    let plan = arrange::capture(&f.p, f.d, &BTreeMap::from([(f.n, f.w), (yn, y)]), f.n).unwrap();
+    let placed = arrange::place(&plan, xy(400., 500.), context).unwrap();
+    let mut expected = f.p.clone();
+    let d = expected.diagrams.get_mut(&f.d).unwrap();
+    d.nodes.get_mut(&f.n).unwrap().position = xy(400., 500.);
+    d.nodes.get_mut(&yn).unwrap().position = xy(550., 500.);
+    assert_eq!(
+        roundtrip(
+            &f.p,
+            arrange::finish(&plan, &f.p, &placed).unwrap().unwrap()
+        ),
+        expected
+    );
+}
+
+#[test]
+fn explicit_arrange_preserves_unrelated_folded_interior_diagnostic_boundary() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        let mut m = distributed(layer, true);
+        let performer = if layer == Layer::Oa {
+            Kind::Actor
+        } else {
+            Kind::SystemActor
+        };
+        let d = m.f.p.add_element(performer, layer, "D", None).unwrap();
+        let z =
+            m.f.p
+                .add_element(m.f.p.elements[&m.f.w].kind(), layer, "Hidden Z", None)
+                .unwrap();
+        m.f.p.relate(RelationKind::Allocation, "D owns Z", d, z);
+        let dn = m.f.p.place(m.f.d, d, xy(2500., 100.));
+        m.f.p.place(m.f.d, z, xy(550., 230.));
+        m.f.p
+            .diagrams
+            .get_mut(&m.f.d)
+            .unwrap()
+            .nodes
+            .get_mut(&dn)
+            .unwrap()
+            .collapsed = true;
+        let plan = arrange::capture(&m.f.p, m.f.d, &identities(&m, &[m.a, m.f.n]), m.f.n).unwrap();
+        let placed =
+            arrange::place(&plan, xy(500., 800.), presentation(&m.f.p, m.f.d, None)).unwrap();
+        assert_eq!(
+            roundtrip(
+                &m.f.p,
+                arrange::finish(&plan, &m.f.p, &placed).unwrap().unwrap()
+            ),
+            expected(&m, true)
+        );
+    }
+}
+
+#[test]
+fn explicit_arrange_noop_stale_tamper_target_and_all_selected_headers() {
+    let m = distributed(Layer::Sa, false);
+    let selected = identities(&m, &[m.a, m.f.n]);
+    let plan = arrange::capture(&m.f.p, m.f.d, &selected, m.f.n).unwrap();
+    let context = presentation(&m.f.p, m.f.d, None);
+    let noop = arrange::place(&plan, xy(103., 802.), context).unwrap();
+    assert!(arrange::finish(&plan, &m.f.p, &noop).unwrap().is_none());
+    let mut placed = arrange::place(&plan, xy(500., 800.), context).unwrap();
+    let mut stale = m.f.p.clone();
+    stale.name.push_str(" changed");
+    assert!(matches!(
+        arrange::finish(&plan, &stale, &placed),
+        Err(Refusal::StaleScope)
+    ));
+    placed.diagram.nodes.get_mut(&m.b).unwrap().position.x += 1.;
+    assert!(matches!(
+        arrange::finish(&plan, &m.f.p, &placed),
+        Err(Refusal::StaleScope)
+    ));
+    assert!(
+        arrange::place(
+            &plan,
+            xy(500., 800.),
+            presentation(&m.f.p, m.f.d, Some(m.f.b))
+        )
+        .is_err()
+    );
+    let mut clipped = context;
+    clipped.viewport.position = xy(400., 700.);
+    assert!(
+        arrange::place(&plan, xy(500., 800.), clipped).is_err(),
+        "anchor C visible, other selected A header clipped"
+    );
+    assert!(arrange::place(&plan, xy(f32::NAN, 800.), context).is_err());
+    assert!(arrange::place(&plan, xy(MAX_COORDINATE, 800.), context).is_err());
+}
diff --git a/crates/oa-desktop/src/allocation_drag/tests.rs b/crates/oa-desktop/src/allocation_drag/tests.rs
index 643a9517..e4401bef 100644
--- a/crates/oa-desktop/src/allocation_drag/tests.rs
+++ b/crates/oa-desktop/src/allocation_drag/tests.rs
@@ -5,6 +5,9 @@ use oa_core::source_project::{ProjectLimits, compile_bundle, format_bundle};
 #[path = "group_arrange_experiment.rs"]
 mod group_arrange_experiment;
 
+#[path = "arrange_tests.rs"]
+mod arrange_tests;
+
 struct Fixture {
     p: Project,
     d: Id,