feat(blocks): wire Stretch actions and independent reference evaluation

Author a native Stretch action from a Linear, Polar or XY parameter, a two-corner stretch frame, an object selection and a marker. Preview and retain its frame in BEDIT, with selectable and movable action markers.

Freeze line and planar lightweight-polyline vertex bindings, preserve curved-segment height, move wholly selected objects, and evaluate independent saved INSERTs from their definition. Retain native DWG/DXF data, copied-reference isolation and undo/redo.

Validate with synthetic frame, topology, parameter, history, Test Block, drawing-reference, COPY and roundtrip regressions: 340 block tests pass (6 existing opt-in ignored), plus 41 dock and 27 viewport tests. Other entity types, Polar Stretch, custom multipliers and chaining remain unsupported.

src/app/block_actions.rs

@@ -38,7 +38,7 @@ impl OpenCADStudio {
         };
         if !args.is_empty() && kind.is_none() {
             self.command_line.push_error(
-                crate::t!("Supported actions: Move, Scale, Rotate, Flip. Other action types are not wired yet.")
+                crate::t!("Supported actions: Move, Scale, Stretch, Rotate, Flip. Other action types are not wired yet.")
                     .as_ref(),
             );
             return Task::none();
@@ -76,6 +76,7 @@ impl OpenCADStudio {
                 parameter,
                 targets,
                 location,
+                frame,
             } => {
                 if self.tabs[i].id != document
                     || self.tabs[i]
@@ -90,8 +91,15 @@ impl OpenCADStudio {
                     return Task::none();
                 }
                 let mut staged = self.tabs[i].scene.document.clone();
-                match actions::create(&mut staged, definition, kind, parameter, &targets, location)
-                {
+                match actions::create_with_frame(
+                    &mut staged,
+                    definition,
+                    kind,
+                    parameter,
+                    &targets,
+                    location,
+                    frame,
+                ) {
                     Ok(_) => {
                         self.push_undo_snapshot(i, &format!("{} action", kind.name()));
                         self.tabs[i].scene.document = staged;

src/app/block_editor_tests.rs

@@ -59,6 +59,138 @@ fn feed(app: &mut OpenCADStudio, text: &str) {
     let _ = app.update(Message::CommandSubmit);
 }
 
+#[test]
+fn block_actions_stretch_frame_selection_history_test_and_saved_grip() {
+    use crate::scene::block_actions::{self as actions, Kind};
+    let (mut app, reference) = fixture();
+    begin(&mut app, reference);
+    let i = app.active_tab;
+    let def = app.tabs[i].active_block_edit_session().unwrap().br_handle;
+    let _ = app.run_command_line("BPARAMETER LINEAR 0,0 10,0 5,2");
+    let p = actions::parameters(&app.tabs[i].scene.document, def, Kind::Stretch)[0].clone();
+    let before = app.tabs[i].scene.document.clone();
+    // A half-authored frame and Escape create neither objects nor history.
+    let depth = app.tabs[i].history.undo_stack.len();
+    let _ = app.dispatch_command("BACTION Stretch");
+    feed(&mut app, &p.name);
+    feed(&mut app, "0.5,-1");
+    let _ = app.update(Message::CommandEscape);
+    assert_eq!(app.tabs[i].scene.document, before);
+    assert_eq!(app.tabs[i].history.undo_stack.len(), depth);
+    let _ = app.dispatch_command("BACTION Stretch");
+    feed(&mut app, &p.name);
+    assert!(!app.tabs[i]
+        .active_cmd
+        .as_ref()
+        .unwrap()
+        .is_selection_gathering());
+    feed(&mut app, "0.5,-1");
+    feed(&mut app, "0.5,1"); // zero-width error retains first corner
+    assert!(!app.tabs[i]
+        .active_cmd
+        .as_ref()
+        .unwrap()
+        .is_selection_gathering());
+    feed(&mut app, "2,1");
+    assert!(app.tabs[i]
+        .active_cmd
+        .as_ref()
+        .unwrap()
+        .is_selection_gathering());
+    let targets = members(&app);
+    let _ = app.feed_command(crate::command::StepInput::SelectionComplete(
+        targets.clone(),
+    ));
+    let _ = app.feed_command(crate::command::StepInput::Enter);
+    feed(&mut app, "3,4");
+    assert!(app.tabs[i].active_cmd.is_none());
+    assert_eq!(app.tabs[i].history.undo_stack.len(), depth + 1);
+    let action = actions::actions(&app.tabs[i].scene.document, def)[0].0;
+    assert_eq!(
+        actions::frame_outline(&app.tabs[i].scene.document, action).len(),
+        4
+    );
+    app.undo_steps(1);
+    assert!(actions::actions(&app.tabs[i].scene.document, def).is_empty());
+    app.redo_steps(1);
+    let editor = app.tabs[i].scene.document.clone();
+    let _ = app.dispatch_command("BTESTBLOCK");
+    let ti = app.active_tab;
+    let test_insert = app.tabs[ti].block_test.as_ref().unwrap().insert;
+    app.tabs[ti].scene.selected.insert(test_insert);
+    app.refresh_properties();
+    let grip = app.tabs[ti]
+        .selected_grips
+        .iter()
+        .find(|g| super::block_actions::is_test_grip(g.id))
+        .unwrap()
+        .id;
+    assert!(app.start_test_action_grip(test_insert, grip));
+    feed(&mut app, "12,0");
+    let EntityType::Line(line) = app.tabs[ti].scene.document.get_entity(targets[0]).unwrap() else {
+        panic!()
+    };
+    assert_eq!(line.start, Vector3::ZERO);
+    assert_eq!(line.end, Vector3::new(3., 0., 0.));
+    let _ = app.dispatch_command("BCLOSETESTBLOCK");
+    assert_eq!(app.tabs[i].scene.document, editor);
+    let _ = app.dispatch_command("BSAVE");
+    let _ = app.dispatch_command("BCLOSE");
+    app.tabs[i].scene.selected.insert(reference);
+    app.refresh_properties();
+    let grip = app.tabs[i]
+        .selected_grips
+        .iter()
+        .find(|g| super::block_actions::is_test_grip(g.id))
+        .unwrap()
+        .id;
+    let depth = app.tabs[i].history.undo_stack.len();
+    assert!(app.start_test_action_grip(reference, grip));
+    feed(&mut app, "15,0");
+    assert_eq!(app.tabs[i].history.undo_stack.len(), depth + 1);
+    let changed = app.tabs[i].scene.document.clone();
+    let EntityType::Insert(insert) = changed.get_entity(reference).unwrap() else {
+        panic!()
+    };
+    let member = changed
+        .block_records
+        .get(&insert.block_name)
+        .unwrap()
+        .entity_handles[0];
+    let EntityType::Line(line) = changed.get_entity(member).unwrap() else {
+        panic!()
+    };
+    assert_eq!(line.start, Vector3::ZERO);
+    assert_eq!(line.end, Vector3::new(6., 0., 0.));
+    assert_eq!(
+        changed.get_entity(targets[0]),
+        editor.get_entity(targets[0])
+    );
+    app.undo_steps(1);
+    assert_eq!(
+        app.tabs[i].scene.document.get_entity(reference),
+        editor.get_entity(reference)
+    );
+    app.redo_steps(1);
+    assert_eq!(
+        app.tabs[i].scene.document.get_entity(member),
+        changed.get_entity(member)
+    );
+    let bytes = codec::DwgWriter::write_to_vec(&changed).unwrap();
+    app.tabs[i].scene.document = codec::DwgReader::from_stream(std::io::Cursor::new(bytes))
+        .read()
+        .unwrap();
+    begin(&mut app, reference);
+    assert_eq!(
+        app.tabs[i].active_block_edit_session().unwrap().br_handle,
+        def
+    );
+    assert_eq!(
+        actions::frame_outline(&app.tabs[i].scene.document, action).len(),
+        4
+    );
+}
+
 #[test]
 fn block_parameters_rotation_only_save_close_reopen_then_flip() {
     use crate::scene::block_actions::{self as actions, Kind};
@@ -903,6 +1035,7 @@ fn block_actions_rejected_outside_editor_preserve_running_command_and_stale_resu
         parameter: p,
         targets: members(&app),
         location: glam::DVec3::ZERO,
+        frame: None,
     });
     assert_eq!(app.tabs[i].scene.document, before);
     let _ = app.dispatch_command("LINE");

src/app/dock/tests.rs

@@ -1244,6 +1244,27 @@ fn block_actions_palette_controls_require_compatible_parameters_and_start_comman
     });
 }
 
+#[test]
+fn block_actions_stretch_palette_requires_distance_parameter() {
+    with_stack(|| {
+        let mut app = authoring_app();
+        let _ = app.dispatch_command("BAUTHORPALETTE");
+        app.authoring_palette_tab = crate::ui::window::authoring_palettes::Tab::Actions;
+        let point = authoring_control(&app, "authoring-tool-stretch-action");
+        authoring_click(&mut app, point);
+        assert!(app.tabs[app.active_tab].active_cmd.is_none());
+        let _ = app.run_command_line("BPARAMETER LINEAR 0,0 10,0 5,2");
+        let point = authoring_control(&app, "authoring-tool-stretch-action");
+        authoring_click(&mut app, point);
+        assert!(app.tabs[app.active_tab]
+            .active_cmd
+            .as_ref()
+            .unwrap()
+            .prompt()
+            .contains("Stretch"));
+    });
+}
+
 #[test]
 fn block_actions_rotate_flip_palette_requires_matching_parameters() {
     with_stack(|| {

src/app/dock/view.rs

@@ -415,6 +415,7 @@ impl OpenCADStudio {
                     self.action_error(Some(crate::scene::block_actions::Kind::Scale)),
                     self.action_error(Some(crate::scene::block_actions::Kind::Rotate)),
                     self.action_error(Some(crate::scene::block_actions::Kind::Flip)),
+                    self.action_error(Some(crate::scene::block_actions::Kind::Stretch)),
                 )
             }
             crate::ui::dock::PanelId::BlockPalette => {

src/app/view/mod.rs

@@ -1203,8 +1203,19 @@ bg={bg_ms:.1}ms n={view_count}"
                             session.br_handle,
                         )
                         .into_iter()
-                        .map(|(_, action, _, _)| {
+                        .map(|(handle, action, _, _)| {
                             let mut g = crate::scene::block_distance_parameter::Graphic::default();
+                            let frame = crate::scene::block_actions::frame_outline(
+                                &tab.scene.document,
+                                handle,
+                            );
+                            g.lines.extend(
+                                frame
+                                    .iter()
+                                    .zip(frame.iter().cycle().skip(1))
+                                    .take(frame.len())
+                                    .map(|(a, b)| [*a, *b]),
+                            );
                             g.grips.push((action.display_location, false));
                             g.labels
                                 .push((action.display_location, action.element.name.clone()));

src/command.rs

@@ -1528,6 +1528,7 @@ pub enum CmdResult {
         parameter: Handle,
         targets: Vec<Handle>,
         location: DVec3,
+        frame: Option<[DVec3; 2]>,
     },
     EvaluateBlockParameter {
         insert: Option<Handle>,

src/modules/block_editor/action.rs

@@ -16,6 +16,7 @@ pub(crate) struct ActionCommand {
     parameter: Option<Handle>,
     targets: Vec<Handle>,
     selecting: bool,
+    frame: Vec<DVec3>,
     context: Option<PointPickContext>,
 }
 impl ActionCommand {
@@ -33,6 +34,7 @@ impl ActionCommand {
             parameter: None,
             targets: vec![],
             selecting: false,
+            frame: vec![],
             context: None,
         }
     }
@@ -43,7 +45,7 @@ impl ActionCommand {
             );
         }
         self.parameter = Some(p.handle);
-        self.selecting = true;
+        self.selecting = self.kind != Some(Kind::Stretch);
         CmdResult::DeselectAndContinue
     }
 }
@@ -62,7 +64,8 @@ impl CadCommand for ActionCommand {
     }
     fn prompt(&self) -> String {
         if self.kind.is_none() {
-            return crate::t!("BACTION  Enter action type [Move/Scale/Rotate/Flip]:").into_owned();
+            return crate::t!("BACTION  Enter action type [Move/Scale/Stretch/Rotate/Flip]:")
+                .into_owned();
         }
         if self.parameter.is_none() {
             return crate::tf!(
@@ -71,11 +74,17 @@ impl CadCommand for ActionCommand {
             )
             .into_owned();
         }
-        crate::t!(if self.selecting {
-            "BACTION  Select objects for the action, then press Enter:"
-        } else {
-            "BACTION  Specify action marker location:"
-        })
+        crate::t!(
+            if self.kind == Some(Kind::Stretch) && self.frame.is_empty() {
+                "BACTION  Specify first corner of stretch frame:"
+            } else if self.kind == Some(Kind::Stretch) && self.frame.len() == 1 {
+                "BACTION  Specify opposite corner of stretch frame:"
+            } else if self.selecting {
+                "BACTION  Select objects for the action, then press Enter:"
+            } else {
+                "BACTION  Specify action marker location:"
+            }
+        )
         .into_owned()
     }
     fn options(&self) -> Vec<CmdOption> {
@@ -83,6 +92,7 @@ impl CadCommand for ActionCommand {
             vec![
                 CmdOption::new("Move", "Move"),
                 CmdOption::new("Scale", "Scale"),
+                CmdOption::new("Stretch", "Stretch"),
                 CmdOption::new("Rotate", "Rotate"),
                 CmdOption::new("Flip", "Flip"),
             ]
@@ -97,7 +107,7 @@ impl CadCommand for ActionCommand {
                 CmdResult::NeedPoint
             } else {
                 CmdResult::ReportError(
-                    crate::t!("Choose Move, Scale, Rotate or Flip.").into_owned(),
+                    crate::t!("Choose Move, Scale, Stretch, Rotate or Flip.").into_owned(),
                 )
             });
         }
@@ -149,6 +159,35 @@ impl CadCommand for ActionCommand {
                 )
             });
         }
+        if self.kind == Some(Kind::Stretch) && self.frame.len() < 2 {
+            let plane = self
+                .candidates
+                .iter()
+                .find(|p| Some(p.handle) == self.parameter)
+                .unwrap()
+                .end
+                .z;
+            if !point.is_finite() || (point.z - plane).abs() > 1e-8 {
+                return CmdResult::ReportError(
+                    crate::t!("Specify a finite corner in the parameter's XY plane.").into_owned(),
+                );
+            }
+            if self
+                .frame
+                .first()
+                .is_some_and(|a| (point.x - a.x).abs() < 1e-9 || (point.y - a.y).abs() < 1e-9)
+            {
+                return CmdResult::ReportError(
+                    crate::t!("The stretch frame needs a nonzero width and height.").into_owned(),
+                );
+            }
+            self.frame.push(point);
+            if self.frame.len() == 2 {
+                self.selecting = true;
+                return CmdResult::DeselectAndContinue;
+            }
+            return CmdResult::NeedPoint;
+        }
         if self.selecting {
             return CmdResult::NeedPoint;
         }
@@ -164,8 +203,26 @@ impl CadCommand for ActionCommand {
             parameter: self.parameter.unwrap(),
             targets: self.targets.clone(),
             location: point,
+            frame: (self.frame.len() == 2).then(|| [self.frame[0], self.frame[1]]),
         }
     }
+    fn on_preview_wires(&mut self, point: DVec3) -> Vec<crate::scene::WireModel> {
+        let Some(a) = self.frame.first().filter(|_| point.is_finite()) else {
+            return vec![];
+        };
+        let b = self.frame.get(1).copied().unwrap_or(point);
+        vec![crate::scene::WireModel::solid_f64(
+            "preview_stretch_frame".into(),
+            vec![
+                a.to_array(),
+                [b.x, a.y, a.z],
+                [b.x, b.y, a.z],
+                [a.x, b.y, a.z],
+            ],
+            crate::scene::WireModel::CYAN,
+            true,
+        )]
+    }
     fn is_selection_gathering(&self) -> bool {
         self.selecting
     }

src/modules/draw/modify/stretch.rs

@@ -277,7 +277,13 @@ pub fn stretch_entity(
 
 /// The bulge of the segment from vertex `k` once its ends moved from
 /// `before` to `after`: the arc keeps its height, bulge · chord / 2.
-fn held_bulge(bulge: f64, before: &[[f64; 2]], after: &[[f64; 2]], k: usize, closed: bool) -> f64 {
+pub(crate) fn held_bulge(
+    bulge: f64,
+    before: &[[f64; 2]],
+    after: &[[f64; 2]],
+    k: usize,
+    closed: bool,
+) -> f64 {
     let next = if k + 1 < before.len() {
         k + 1
     } else if closed {

src/scene/block_actions.rs

@@ -1,14 +1,15 @@
-//! Native Move/Scale/Rotate/Flip authoring and deterministic block evaluation.
+//! Native Move/Scale/Stretch/Rotate/Flip authoring and deterministic block evaluation.
 use super::block_authoring::{self as authoring, *};
 use codec::objects::{
     BlockAction, BlockActionOffsets, BlockActionWithBasePoint, BlockBasePointAction,
     BlockConnection, BlockElement, BlockEvalValue, BlockMoveAction, BlockFlipAction,
-    DynamicBlockData, ObjectType,
+    BlockStretchAction, DynamicBlockData, ObjectType,
 };
 use codec::types::{Transform, Vector3};
 use codec::{CadDocument, EntityType, Handle};
 use glam::DVec3;
 pub(crate) mod instance;
+mod stretch;
 #[cfg(test)]
 mod tests;
 
@@ -18,6 +19,7 @@ pub enum Kind {
     Scale,
     Rotate,
     Flip,
+    Stretch,
 }
 impl Kind {
     pub(crate) fn parse(s: &str) -> Option<Self> {
@@ -26,6 +28,7 @@ impl Kind {
             "SCALE" | "S" => Some(Self::Scale),
             "ROTATE" | "R" => Some(Self::Rotate),
             "FLIP" | "F" => Some(Self::Flip),
+            "STRETCH" | "ST" => Some(Self::Stretch),
             _ => None,
         }
     }
@@ -35,6 +38,7 @@ impl Kind {
             Self::Scale => "Scale",
             Self::Rotate => "Rotate",
             Self::Flip => "Flip",
+            Self::Stretch => "Stretch",
         }
     }
 }
@@ -78,6 +82,7 @@ pub(crate) fn all_parameters(doc: &CadDocument, definition: Handle) -> Vec<Param
 pub(crate) fn compatible(p: &Parameter, kind: Kind) -> bool {
     match kind {
         Kind::Move => !p.rotation && !p.flip,
+        Kind::Stretch => !p.rotation && !p.flip && !p.point,
         Kind::Scale => !p.rotation && !p.flip && !p.point && !p.xy,
         Kind::Rotate => p.rotation,
         Kind::Flip => p.flip,
@@ -342,6 +347,7 @@ pub(crate) fn supported(e: &EntityType) -> bool {
             | EntityType::MText(_)
     )
 }
+#[cfg(test)]
 pub(crate) fn create(
     doc: &mut CadDocument,
     definition: Handle,
@@ -349,6 +355,18 @@ pub(crate) fn create(
     parameter: Handle,
     targets: &[Handle],
     location: DVec3,
+) -> Result<Handle, &'static str> {
+    create_with_frame(doc, definition, kind, parameter, targets, location, None)
+}
+
+pub(crate) fn create_with_frame(
+    doc: &mut CadDocument,
+    definition: Handle,
+    kind: Kind,
+    parameter: Handle,
+    targets: &[Handle],
+    location: DVec3,
+    frame: Option<[DVec3; 2]>,
 ) -> Result<Handle, &'static str> {
     if !location.is_finite() {
         return Err("Specify a finite action location.");
@@ -374,6 +392,19 @@ pub(crate) fn create(
     }) {
         return Err("This milestone supports lines, polylines, arcs, circles, ellipses, points and text belonging to this block.");
     }
+    let stretch_binding = if kind == Kind::Stretch {
+        if (location.z - p.end.z).abs() > 1e-8 {
+            return Err("Place the Stretch marker in the parameter's XY plane.");
+        }
+        Some(stretch::bind(
+            doc,
+            targets,
+            frame.ok_or("Specify a stretch frame before selecting objects.")?,
+            p.end.z,
+        )?)
+    } else {
+        None
+    };
     let mut staged = doc.clone();
     let (graph, slots) = authoring::prepare(&mut staged, definition)?;
     let (dxf, cpp) = match kind {
@@ -381,6 +412,7 @@ pub(crate) fn create(
         Kind::Scale => ("BLOCKSCALEACTION", "AcDbBlockScaleAction"),
         Kind::Rotate => ("BLOCKROTATEACTION", "AcDbBlockRotationAction"),
         Kind::Flip => ("BLOCKFLIPACTION", "AcDbBlockFlipAction"),
+        Kind::Stretch => ("BLOCKSTRETCHACTION", "AcDbBlockStretchAction"),
     };
     register_classes(&mut staged, &[(dxf, cpp, 55)]);
     let handle = staged.allocate_handle();
@@ -404,6 +436,21 @@ pub(crate) fn create(
         name: name.into(),
     };
     let data = match kind {
+        Kind::Stretch => {
+            let (points, handles) = stretch_binding.unwrap();
+            DynamicBlockData::StretchAction(BlockStretchAction {
+                action,
+                connections: [connection("EndXDelta"), connection("EndYDelta")],
+                points,
+                handles,
+                codes: vec![],
+                offsets: BlockActionOffsets {
+                    distance_multiplier: 1.,
+                    angle_offset: 0.,
+                    flags: 0,
+                },
+            })
+        }
         Kind::Move => DynamicBlockData::MoveAction(BlockMoveAction {
             action,
             connections: if p.point {
@@ -489,6 +536,9 @@ pub(crate) fn actions(
                 DynamicBlockData::MoveAction(a) => {
                     Some((o.handle, &a.action, Kind::Move, a.connections[0].code))
                 }
+                DynamicBlockData::StretchAction(a) => {
+                    Some((o.handle, &a.action, Kind::Stretch, a.connections[0].code))
+                }
                 DynamicBlockData::FlipAction(a) => {
                     Some((o.handle, &a.action, Kind::Flip, a.connections[0].code))
                 }
@@ -505,6 +555,16 @@ pub(crate) fn actions(
         })
         .collect()
 }
+pub(crate) fn frame_outline(doc: &CadDocument, handle: Handle) -> Vec<Vector3> {
+    let Some(ObjectType::DynamicBlock(o)) = doc.objects.get(&handle) else {
+        return vec![];
+    };
+    let DynamicBlockData::StretchAction(a) = &o.data else {
+        return vec![];
+    };
+    stretch::outline(&a.points, a.action.display_location.z)
+}
+
 pub(crate) fn reframe(doc: &mut CadDocument, definition: Handle, t: &Transform) -> usize {
     let handles = actions(doc, definition)
         .iter()
@@ -518,6 +578,17 @@ pub(crate) fn reframe(doc: &mut CadDocument, definition: Handle, t: &Transform)
             DynamicBlockData::MoveAction(a) => {
                 a.action.display_location = t.apply(a.action.display_location)
             }
+            DynamicBlockData::StretchAction(a) => {
+                let plane = a.action.display_location.z;
+                a.action.display_location = t.apply(a.action.display_location);
+                a.points = stretch::outline(&a.points, plane)
+                    .into_iter()
+                    .map(|p| {
+                        let p = t.apply(p);
+                        codec::types::Vector2::new(p.x, p.y)
+                    })
+                    .collect();
+            }
             DynamicBlockData::FlipAction(a) => {
                 a.action.display_location = t.apply(a.action.display_location)
             }
@@ -613,8 +684,10 @@ pub(crate) fn evaluate_value(
 ) -> Result<bool, &'static str> {
     let graph = authoring::graph(baseline, definition)?
         .ok_or("The block authoring graph is unavailable.")?;
-    if baseline.objects.values().any(|o|matches!(o,ObjectType::DynamicBlock(o) if o.owner==graph && matches!(&o.data,
-        DynamicBlockData::StretchAction(_)|DynamicBlockData::PolarStretchAction(_)|DynamicBlockData::ArrayAction(_)))) {
+    if baseline.objects.values().any(|o| {
+        matches!(o,ObjectType::DynamicBlock(o) if o.owner==graph && matches!(&o.data,
+        DynamicBlockData::PolarStretchAction(_)|DynamicBlockData::ArrayAction(_)))
+    }) {
         return Err("This block contains action types not supported yet.");
     }
     let p = all_parameters(baseline, definition)
@@ -660,7 +733,16 @@ pub(crate) fn evaluate_value(
     set_value(&mut staged, &p, input)?;
     let all = actions(baseline, definition);
     let mut affected = std::collections::BTreeSet::new();
-    for (_, a, _, _) in &all {
+    for (h, a, kind, _) in &all {
+        if *kind == Kind::Stretch {
+            let ObjectType::DynamicBlock(o) = &baseline.objects[h] else {
+                unreachable!()
+            };
+            let DynamicBlockData::StretchAction(s) = &o.data else {
+                unreachable!()
+            };
+            stretch::validate(baseline, s)?;
+        }
         affected.extend(a.dependencies.iter().copied());
     }
     for h in affected {
@@ -688,7 +770,9 @@ pub(crate) fn evaluate_value(
             }
             let end = current(&staged, &q);
             let transform = match kind {
-                Kind::Move => crate::command::EntityTransform::Translate(end - q.end),
+                Kind::Move | Kind::Stretch => {
+                    crate::command::EntityTransform::Translate(end - q.end)
+                }
                 Kind::Rotate => {
                     let a = end - q.base;
                     let b = q.end - q.base;
@@ -805,7 +889,11 @@ pub(crate) fn evaluate_value(
                 }
                 _ => {}
             }
-            super::view::dispatch::apply_transform(&mut entity, &transform);
+            if let DynamicBlockData::StretchAction(s) = &o.data {
+                stretch::apply(&mut entity, s, end - q.end)?;
+            } else {
+                super::view::dispatch::apply_transform(&mut entity, &transform);
+            }
             let bounds = entity.as_entity().bounding_box();
             if !v(bounds.min).is_finite() || !v(bounds.max).is_finite() {
                 return Err("The parameter value produces non-finite geometry.");

src/scene/block_actions/stretch.rs

@@ -0,0 +1,195 @@
+//! A native Stretch action freezes its vertex membership at authoring time.
+use super::*;
+use codec::objects::{BlockStretchAction, BlockStretchHandle};
+use codec::types::Vector2;
+
+pub(crate) fn control_points(e: &EntityType) -> Result<Vec<DVec3>, &'static str> {
+    let points = match e {
+        EntityType::Line(l) => vec![v(l.start), v(l.end)],
+        EntityType::LwPolyline(p) => {
+            let p = crate::entities::curve::lwpolyline_world_xy(p)
+                .ok_or("Stretch requires a planar XY lightweight polyline.")?;
+            p.vertices
+                .iter()
+                .map(|v| DVec3::new(v.location.x, v.location.y, p.elevation))
+                .collect()
+        }
+        _ => return Err("Stretch currently supports lines and planar lightweight polylines."),
+    };
+    if points.is_empty() || points.iter().any(|p| !p.is_finite()) {
+        return Err("Stretch targets need finite vertices.");
+    }
+    Ok(points)
+}
+
+pub(crate) fn bind(
+    doc: &CadDocument,
+    targets: &[Handle],
+    corners: [DVec3; 2],
+    plane: f64,
+) -> Result<(Vec<Vector2>, Vec<BlockStretchHandle>), &'static str> {
+    if corners
+        .iter()
+        .any(|p| !p.is_finite() || (p.z - plane).abs() > 1e-8)
+    {
+        return Err("Specify finite stretch-frame corners in the parameter's XY plane.");
+    }
+    let low = corners[0].min(corners[1]);
+    let high = corners[0].max(corners[1]);
+    if high.x - low.x < 1e-9 || high.y - low.y < 1e-9 {
+        return Err("The stretch frame needs a nonzero width and height.");
+    }
+    let mut bindings = vec![];
+    let mut unique = targets.to_vec();
+    unique.sort();
+    unique.dedup();
+    for handle in unique {
+        let entity = doc
+            .get_entity(handle)
+            .ok_or("A Stretch target is unavailable.")?;
+        let points = control_points(entity)?;
+        if points.iter().any(|p| (p.z - plane).abs() > 1e-8) {
+            return Err("Stretch targets must lie in the parameter's XY plane.");
+        }
+        let indexes = points
+            .iter()
+            .enumerate()
+            .filter(|(_, p)| p.x >= low.x && p.x <= high.x && p.y >= low.y && p.y <= high.y)
+            .map(|(i, _)| i as i32)
+            .collect::<Vec<_>>();
+        if !indexes.is_empty() {
+            bindings.push(BlockStretchHandle { handle, indexes });
+        }
+    }
+    Ok((
+        vec![Vector2::new(low.x, low.y), Vector2::new(high.x, high.y)],
+        bindings,
+    ))
+}
+
+pub(crate) fn validate(doc: &CadDocument, a: &BlockStretchAction) -> Result<(), &'static str> {
+    if a.points.len() < 2
+        || a.points
+            .iter()
+            .any(|p| !p.x.is_finite() || !p.y.is_finite())
+        || a.offsets.distance_multiplier != 1.
+        || a.offsets.angle_offset != 0.
+        || a.offsets.flags != 0
+        || !a.codes.is_empty()
+        || !a.action.action_ids.is_empty()
+        || a.connections[0].code != a.connections[1].code
+        || a.connections[0].name != "EndXDelta"
+        || a.connections[1].name != "EndYDelta"
+    {
+        return Err("This Stretch action uses options or parameter bindings not supported yet.");
+    }
+    let mut seen = std::collections::BTreeSet::new();
+    for binding in &a.handles {
+        if !a.action.dependencies.contains(&binding.handle) || !seen.insert(binding.handle) {
+            return Err("The Stretch action has invalid target bindings.");
+        }
+        let count = control_points(
+            doc.get_entity(binding.handle)
+                .ok_or("A Stretch target is unavailable.")?,
+        )?
+        .len();
+        let unique = binding
+            .indexes
+            .iter()
+            .copied()
+            .collect::<std::collections::BTreeSet<_>>();
+        if unique.len() != binding.indexes.len()
+            || binding
+                .indexes
+                .iter()
+                .any(|i| *i < 0 || *i as usize >= count)
+        {
+            return Err("A Stretch vertex binding no longer matches its object.");
+        }
+    }
+    // Selected objects without a partial vertex binding move as a whole.
+    for h in &a.action.dependencies {
+        control_points(
+            doc.get_entity(*h)
+                .ok_or("A Stretch target is unavailable.")?,
+        )?;
+    }
+    Ok(())
+}
+
+pub(crate) fn apply(
+    e: &mut EntityType,
+    a: &BlockStretchAction,
+    delta: DVec3,
+) -> Result<(), &'static str> {
+    let Some(binding) = a
+        .handles
+        .iter()
+        .find(|b| b.handle == e.common().handle && !b.indexes.is_empty())
+    else {
+        crate::scene::view::dispatch::apply_transform(
+            e,
+            &crate::command::EntityTransform::Translate(delta),
+        );
+        return Ok(());
+    };
+    match e {
+        EntityType::Line(l) => {
+            for index in &binding.indexes {
+                let at = match index {
+                    0 => &mut l.start,
+                    1 => &mut l.end,
+                    _ => return Err("Invalid Stretch line endpoint."),
+                };
+                *at = *at + native(delta);
+            }
+        }
+        EntityType::LwPolyline(p) => {
+            let mut world = crate::entities::curve::lwpolyline_world_xy(p)
+                .ok_or("Stretch requires a planar XY lightweight polyline.")?;
+            let before = world
+                .vertices
+                .iter()
+                .map(|v| [v.location.x, v.location.y])
+                .collect::<Vec<_>>();
+            for index in &binding.indexes {
+                let v = world
+                    .vertices
+                    .get_mut(*index as usize)
+                    .ok_or("Invalid Stretch polyline vertex.")?;
+                v.location.x += delta.x;
+                v.location.y += delta.y;
+            }
+            let after = world
+                .vertices
+                .iter()
+                .map(|v| [v.location.x, v.location.y])
+                .collect::<Vec<_>>();
+            for (i, v) in world.vertices.iter_mut().enumerate() {
+                v.bulge = crate::modules::draw::modify::stretch::held_bulge(
+                    v.bulge,
+                    &before,
+                    &after,
+                    i,
+                    world.is_closed,
+                );
+            }
+            *p = world;
+        }
+        _ => return Err("Unsupported Stretch target."),
+    }
+    Ok(())
+}
+
+pub(crate) fn outline(points: &[Vector2], z: f64) -> Vec<Vector3> {
+    let points = if points.len() == 2 {
+        let (a, b) = (points[0], points[1]);
+        vec![a, Vector2::new(b.x, a.y), b, Vector2::new(a.x, b.y)]
+    } else {
+        points.to_vec()
+    };
+    points
+        .into_iter()
+        .map(|p| Vector3::new(p.x, p.y, z))
+        .collect()
+}

src/scene/block_actions/tests.rs

@@ -605,3 +605,264 @@ fn block_actions_reframe_moves_markers_and_retains_targets_and_connections() {
     assert_eq!(s.action.action.dependencies, b.action.action.dependencies);
     assert_eq!(s.connections, b.connections);
 }
+
+fn stretch_fixture() -> (CadDocument, Handle, Vec<Handle>, Handle, Handle) {
+    let mut scene = Scene::new();
+    let mut poly = codec::entities::LwPolyline::from_points(vec![
+        codec::types::Vector2::new(0., 1.),
+        codec::types::Vector2::new(10., 1.),
+        codec::types::Vector2::new(10., 3.),
+        codec::types::Vector2::new(0., 3.),
+    ]);
+    poly.is_closed = true;
+    poly.vertices[0].bulge = 0.2;
+    scene.define_block_raw(
+        "STRETCH",
+        Vector3::ZERO,
+        vec![
+            EntityType::Line(codec::entities::Line::from_points(
+                Vector3::ZERO,
+                Vector3::new(10., 0., 0.),
+            )),
+            EntityType::LwPolyline(poly),
+            EntityType::Line(codec::entities::Line::from_points(
+                Vector3::new(20., 0., 0.),
+                Vector3::new(21., 0., 0.),
+            )),
+        ],
+    );
+    let br = scene.document.block_records.get("STRETCH").unwrap();
+    let (def, handles) = (br.handle, br.entity_handles.clone());
+    let mut doc = scene.document;
+    let p = linear(&mut doc, def);
+    let action = create_with_frame(
+        &mut doc,
+        def,
+        Kind::Stretch,
+        p,
+        &handles,
+        DVec3::new(5., 4., 0.),
+        Some([DVec3::new(9., -1., 0.), DVec3::new(11., 4., 0.)]),
+    )
+    .unwrap();
+    (doc, def, handles, p, action)
+}
+
+#[test]
+fn block_actions_stretch_frozen_vertices_polyline_and_whole_objects_roundtrip() {
+    let (doc, def, handles, p, action) = stretch_fixture();
+    let ObjectType::DynamicBlock(o) = &doc.objects[&action] else {
+        panic!()
+    };
+    let DynamicBlockData::StretchAction(a) = &o.data else {
+        panic!()
+    };
+    assert_eq!(a.handles[0].indexes, vec![1]);
+    assert_eq!(a.handles[1].indexes, vec![1, 2]);
+    assert_eq!(a.action.dependencies, handles);
+    let mut evaluated = doc.clone();
+    for x in [20., 30., 12.] {
+        evaluate(&mut evaluated, &doc, def, p, DVec3::new(x, 0., 0.)).unwrap();
+        let EntityType::Line(line) = evaluated.get_entity(handles[0]).unwrap() else {
+            panic!()
+        };
+        assert_eq!(line.start, Vector3::ZERO);
+        assert_eq!(line.end, Vector3::new(x, 0., 0.));
+        // Entirely outside the frame but explicitly in the action selection.
+        assert_eq!(start(&evaluated, handles[2]), Vector3::new(x + 10., 0., 0.));
+        let EntityType::LwPolyline(poly) = evaluated.get_entity(handles[1]).unwrap() else {
+            panic!()
+        };
+        assert_eq!(poly.vertices[0].location.x, 0.);
+        assert_eq!(poly.vertices[1].location.x, x);
+        assert_eq!(poly.vertices[2].location.x, x);
+        assert_eq!(poly.vertices[3].location.x, 0.);
+        // Preserve the curved segment's sagitta when its chord changes.
+        assert!((poly.vertices[0].bulge * x / 2. - 1.).abs() < 1e-8);
+    }
+    for reopened in [
+        DwgReader::from_stream(Cursor::new(DwgWriter::write_to_vec(&doc).unwrap()))
+            .read()
+            .unwrap(),
+        DxfReader::from_reader(Cursor::new(DxfWriter::new(&doc).write_to_vec().unwrap()))
+            .unwrap()
+            .read()
+            .unwrap(),
+    ] {
+        assert_eq!(reopened.objects[&action], doc.objects[&action]);
+        let mut changed = reopened.clone();
+        evaluate(&mut changed, &reopened, def, p, DVec3::new(14., 0., 0.)).unwrap();
+        let EntityType::Line(line) = changed.get_entity(handles[0]).unwrap() else {
+            panic!()
+        };
+        assert_eq!(line.end, Vector3::new(14., 0., 0.));
+    }
+}
+
+#[test]
+fn block_actions_stretch_saved_reference_independence_copy_and_reopen() {
+    let (mut doc, def, handles, p, _) = stretch_fixture();
+    let a = doc
+        .add_entity(EntityType::Insert(codec::entities::Insert::new(
+            "STRETCH",
+            Vector3::ZERO,
+        )))
+        .unwrap();
+    let b = doc
+        .add_entity(EntityType::Insert(codec::entities::Insert::new(
+            "STRETCH",
+            Vector3::new(40., 0., 0.),
+        )))
+        .unwrap();
+    let original = doc.clone();
+    doc = instance::evaluate(&doc, a, p, DVec3::new(18., 0., 0.))
+        .unwrap()
+        .unwrap();
+    assert_eq!(doc.get_entity(handles[0]), original.get_entity(handles[0]));
+    assert_eq!(doc.get_entity(b), original.get_entity(b));
+    let mut scene = Scene::new();
+    scene.document = doc;
+    let c = scene.copy_entities(
+        &[a],
+        &crate::command::EntityTransform::Translate(DVec3::new(60., 0., 0.)),
+    )[0];
+    let mut doc = scene.document;
+    let EntityType::Insert(ins) = doc.get_entity(a).unwrap() else {
+        panic!()
+    };
+    let a_member = doc
+        .block_records
+        .get(&ins.block_name)
+        .unwrap()
+        .entity_handles[0];
+    doc = instance::evaluate(&doc, c, p, DVec3::new(22., 0., 0.))
+        .unwrap()
+        .unwrap();
+    let EntityType::Line(line) = doc.get_entity(a_member).unwrap() else {
+        panic!()
+    };
+    assert_eq!(line.end, Vector3::new(18., 0., 0.));
+    let reopened = DwgReader::from_stream(Cursor::new(DwgWriter::write_to_vec(&doc).unwrap()))
+        .read()
+        .unwrap();
+    let parameter = parameters(&reopened, def, Kind::Stretch)[0].clone();
+    assert_eq!(
+        instance::current(&reopened, c, &parameter).unwrap(),
+        DVec3::new(22., 0., 0.)
+    );
+    let changed = instance::evaluate(&reopened, c, p, DVec3::new(13., 0., 0.))
+        .unwrap()
+        .unwrap();
+    let EntityType::Insert(ins) = changed.get_entity(c).unwrap() else {
+        panic!()
+    };
+    let EntityType::Line(line) = changed
+        .get_entity(
+            changed
+                .block_records
+                .get(&ins.block_name)
+                .unwrap()
+                .entity_handles[0],
+        )
+        .unwrap()
+    else {
+        panic!()
+    };
+    assert_eq!(line.end, Vector3::new(13., 0., 0.));
+}
+
+#[test]
+fn block_actions_stretch_invalid_frame_binding_and_options_are_atomic() {
+    let (mut doc, def, handles, p, action) = stretch_fixture();
+    let before = doc.clone();
+    for frame in [
+        None,
+        Some([DVec3::ZERO, DVec3::X]),
+        Some([DVec3::ZERO, DVec3::splat(f64::NAN)]),
+    ] {
+        assert!(create_with_frame(
+            &mut doc,
+            def,
+            Kind::Stretch,
+            p,
+            &handles,
+            DVec3::ZERO,
+            frame
+        )
+        .is_err());
+        assert_eq!(doc, before);
+    }
+    for corrupt in [0, 1, 2] {
+        let mut invalid = doc.clone();
+        let ObjectType::DynamicBlock(o) = invalid.objects.get_mut(&action).unwrap() else {
+            panic!()
+        };
+        let DynamicBlockData::StretchAction(a) = &mut o.data else {
+            panic!()
+        };
+        match corrupt {
+            0 => a.handles[0].indexes = vec![99],
+            1 => a.offsets.distance_multiplier = 2.,
+            _ => a.connections[0].name = "BaseXDelta".into(),
+        }
+        let baseline = invalid.clone();
+        assert!(evaluate(&mut invalid, &baseline, def, p, DVec3::new(12., 0., 0.)).is_err());
+        assert_eq!(invalid, baseline);
+    }
+}
+
+#[test]
+fn block_actions_stretch_polar_xy_and_reframed_marker_keep_native_bindings() {
+    for kind in [distance::Kind::Polar, distance::Kind::XY] {
+        let (mut doc, def, targets) = fixture();
+        let p = distance::create(
+            &mut doc,
+            def,
+            kind,
+            Vector3::ZERO,
+            Vector3::new(10., 1., 0.),
+            Vector3::new(5., 2., 0.),
+        )
+        .unwrap();
+        let action = create_with_frame(
+            &mut doc,
+            def,
+            Kind::Stretch,
+            p,
+            &targets[..1],
+            DVec3::new(3., 4., 0.),
+            Some([DVec3::new(1.5, -1., 0.), DVec3::new(2.5, 1., 0.)]),
+        )
+        .unwrap();
+        let baseline = doc.clone();
+        evaluate(&mut doc, &baseline, def, p, DVec3::new(12., 4., 0.)).unwrap();
+        let EntityType::Line(line) = doc.get_entity(targets[0]).unwrap() else {
+            panic!()
+        };
+        assert_eq!(line.start, Vector3::UNIT_X);
+        assert!(line.end.distance(&Vector3::new(4., 3., 0.)) < 1e-8);
+        super::super::block_authoring::edit::move_part(
+            &mut doc,
+            def,
+            action,
+            super::super::block_authoring::edit::Part::Point,
+            Vector3::new(6., 7., 0.),
+        )
+        .unwrap();
+        let frame = frame_outline(&doc, action);
+        assert_eq!(frame[0], Vector3::new(1.5, -1., 0.));
+        reframe(
+            &mut doc,
+            def,
+            &Transform::from_translation(Vector3::new(-2., -3., 0.)),
+        );
+        assert_eq!(frame_outline(&doc, action)[0], Vector3::new(-0.5, -4., 0.));
+        let ObjectType::DynamicBlock(o) = &doc.objects[&action] else {
+            panic!()
+        };
+        let DynamicBlockData::StretchAction(a) = &o.data else {
+            panic!()
+        };
+        assert_eq!(a.handles[0].indexes, vec![1]);
+    }
+}

src/scene/block_authoring/edit.rs

@@ -104,7 +104,18 @@ pub fn items(doc: &CadDocument, definition: Handle) -> Vec<Item> {
         result.push(single(p.handle, p.name.clone(), p.def_point));
     }
     for (handle, p, _, _) in crate::scene::block_actions::actions(doc, definition) {
-        result.push(single(handle, p.element.name.clone(), p.display_location));
+        let mut item = single(handle, p.element.name.clone(), p.display_location);
+        let frame = crate::scene::block_actions::frame_outline(doc, handle);
+        if !frame.is_empty() {
+            item.graphic.lines.extend(
+                frame
+                    .iter()
+                    .zip(frame.iter().cycle().skip(1))
+                    .take(frame.len())
+                    .map(|(a, b)| [*a, *b]),
+            );
+        }
+        result.push(item);
     }
     result
 }
@@ -277,6 +288,7 @@ pub fn move_part(
                     }
                 }
                 DynamicBlockData::MoveAction(p) => p.action.display_location = at,
+                DynamicBlockData::StretchAction(p) => p.action.display_location = at,
                 DynamicBlockData::FlipAction(p) => p.action.display_location = at,
                 DynamicBlockData::ScaleAction(p) | DynamicBlockData::RotateAction(p) => {
                     p.action.action.display_location = at

src/scene/camera_ops.rs

@@ -1725,7 +1725,10 @@ impl Scene {
                 .chain(
                     super::block_actions::actions(&self.document, block)
                         .into_iter()
-                        .map(|(_, a, _, _)| a.display_location),
+                        .flat_map(|(handle, a, _, _)| {
+                            std::iter::once(a.display_location)
+                                .chain(super::block_actions::frame_outline(&self.document, handle))
+                        }),
                 );
             for point in locations {
                 let point = glam::DVec3::new(point.x, point.y, point.z);

src/ui/window/authoring_palettes.rs

@@ -198,6 +198,7 @@ fn catalog(
     scale_error: Option<&'static str>,
     rotate_error: Option<&'static str>,
     flip_action_error: Option<&'static str>,
+    stretch_action_error: Option<&'static str>,
 ) -> Element<'static, Message> {
     let (entries, unavailable) = match tab {
         Tab::Parameters => (
@@ -219,8 +220,8 @@ fn catalog(
         let orientation_error = if *label=="Flip" {flip_error} else {point_error};
         let single=tab==Tab::Parameters&&matches!(*label,"Lookup"|"Basepoint");
         let lookup_action=tab==Tab::Actions&&*label=="Lookup";
-        let geometry_action=tab==Tab::Actions&&matches!(*label,"Move"|"Scale"|"Rotate"|"Flip");
-        let action_error=match *label {"Scale"=>scale_error,"Rotate"=>rotate_error,"Flip"=>flip_action_error,_=>move_error};
+        let geometry_action=tab==Tab::Actions&&matches!(*label,"Move"|"Scale"|"Stretch"|"Rotate"|"Flip");
+        let action_error=match *label {"Scale"=>scale_error,"Stretch"=>stretch_action_error,"Rotate"=>rotate_error,"Flip"=>flip_action_error,_=>move_error};
         let enabled = (geometry_action&&action_error.is_none())||(single&&point_error.is_none())||(lookup_action&&lookup_error.is_none())||(orientation && orientation_error.is_none()) || (visibility && visibility_error.is_none()) || ((point || distance) && point_error.is_none());
         let base = if enabled {
             icons::semantic(icon, 28.0)
@@ -266,7 +267,7 @@ fn catalog(
         } else if single {
             crate::t!(point_error.unwrap_or(if *label=="Basepoint" {"Place or relocate the dynamic block insertion anchor."}else{"Place a Lookup parameter, then use the Lookup action to edit its property table."})).into_owned()
         } else if geometry_action {
-            crate::t!(action_error.unwrap_or("Select a parameter endpoint, select the objects it controls, then place the action marker. Use the reference parameter grip in the drawing or Test Block.")).into_owned()
+            crate::t!(action_error.unwrap_or(if *label=="Stretch" {"Select a parameter endpoint, define the stretch frame, select its objects, then place the action marker."}else{"Select a parameter endpoint, select the objects it controls, then place the action marker. Use the reference parameter grip in the drawing or Test Block."})).into_owned()
         } else if lookup_action {
             crate::t!(lookup_error.unwrap_or("Create or edit property Lookup tables for this block.")).into_owned()
         } else {
@@ -284,7 +285,7 @@ fn catalog(
         } else if single {
             container(entry).id(if *label=="Lookup" {"authoring-tool-lookup"}else{"authoring-tool-basepoint"}).into()
         } else if geometry_action {
-            container(entry).id(match *label {"Move"=>"authoring-tool-move-action","Scale"=>"authoring-tool-scale-action","Rotate"=>"authoring-tool-rotate-action",_=>"authoring-tool-flip-action"}).into()
+            container(entry).id(match *label {"Move"=>"authoring-tool-move-action","Scale"=>"authoring-tool-scale-action","Rotate"=>"authoring-tool-rotate-action","Stretch"=>"authoring-tool-stretch-action",_=>"authoring-tool-flip-action"}).into()
         } else if lookup_action {
             container(entry).id("authoring-tool-lookup-table").into()
         } else {
@@ -405,6 +406,7 @@ pub fn view(
     scale_error: Option<&'static str>,
     rotate_error: Option<&'static str>,
     flip_action_error: Option<&'static str>,
+    stretch_action_error: Option<&'static str>,
 ) -> Element<'static, Message> {
     let tabs = column(Tab::ALL.into_iter().map(|category| {
         let label = category.label();
@@ -463,7 +465,8 @@ pub fn view(
                 move_error,
                 scale_error,
                 rotate_error,
-                flip_action_error
+                flip_action_error,
+                stretch_action_error
             ))
             .width(Fill)
             .height(Fill),