diff --git a/src/app/automation.rs b/src/app/automation.rs
index 9d230d30c..088493ab7 100644
--- a/src/app/automation.rs
+++ b/src/app/automation.rs
@@ -1801,7 +1801,7 @@ mod tests {
         viewport.id = 2;
         viewport.width = 100.0;
         viewport.height = 50.0;
-        viewport.status.is_on = true;
+        viewport.turn_on();
         scene.add_entity(codec::EntityType::Viewport(viewport));
         for entity in scene.document.entities_mut() {
             if let codec::EntityType::Viewport(viewport) = entity {
diff --git a/src/app/command_driver/tests.rs b/src/app/command_driver/tests.rs
index c5a250660..85e6e3c8b 100644
--- a/src/app/command_driver/tests.rs
+++ b/src/app/command_driver/tests.rs
@@ -935,14 +935,17 @@ mod delobj_tests {
                 expected,
             );
         }
-        assert_eq!(
-            sweep_source_presence(2, crate::command::ExtrudeMode::Surface),
-            (false, false),
-        );
-        assert_eq!(
-            sweep_source_presence(3, crate::command::ExtrudeMode::Surface),
-            (false, true),
-        );
+        // A swept surface is associative by default (SURFACEASSOCIATIVITY 1)
+        // and keeps the profile and path it follows, whatever DELOBJ says;
+        // DELOBJ reaches surfaces only with associativity off, a profile-wide
+        // switch this parallel test leaves alone.
+        assert!(crate::scene::model::sweep_model::surface_associativity());
+        for value in [2, 3] {
+            assert_eq!(
+                sweep_source_presence(value, crate::command::ExtrudeMode::Surface),
+                (true, true),
+            );
+        }
     }
 }
 
diff --git a/src/app/commands/view.rs b/src/app/commands/view.rs
index 3c6bc31dd..1436e1450 100644
--- a/src/app/commands/view.rs
+++ b/src/app/commands/view.rs
@@ -719,7 +719,7 @@ impl OpenCADStudio {
                                             vp.view_height,
                                             vp.height,
                                         ),
-                                        vp.status.is_on,
+                                        vp.is_on(),
                                         vp.status.locked,
                                     ))
                                 } else {
diff --git a/src/app/viewport_dimension_tests.rs b/src/app/viewport_dimension_tests.rs
index 04e09759f..2628f1355 100644
--- a/src/app/viewport_dimension_tests.rs
+++ b/src/app/viewport_dimension_tests.rs
@@ -27,7 +27,7 @@ fn fixture() -> (OpenCADStudio, Handle, ViewportFrame) {
     viewport.view_height = 1000.0;
     viewport.custom_scale = 0.1;
     viewport.view_direction = Vector3::UNIT_Z;
-    viewport.status.is_on = true;
+    viewport.turn_on();
     let viewport = scene.add_entity(EntityType::Viewport(viewport));
     let frame = scene.viewport_frame(viewport).unwrap();
     scene.document.header.dimension_associativity = 2;
@@ -484,7 +484,7 @@ fn viewport_dimension_eligibility_is_shared_and_uses_clipping() {
         first.viewport
     );
     if let Some(EntityType::Viewport(vp)) = scene.document.get_entity_mut(first.viewport) {
-        vp.status.is_on = false;
+        vp.turn_off();
     }
     assert!(scene.viewport_frames_at_paper_point(paper).is_empty());
     assert!(scene.dimension_pick_through_viewport(paper, 0.2).is_none());
diff --git a/src/entities/viewport.rs b/src/entities/viewport.rs
index 3e65cca64..37798bef2 100644
--- a/src/entities/viewport.rs
+++ b/src/entities/viewport.rs
@@ -113,7 +113,7 @@ fn properties(vp: &Viewport) -> Vec<PropSection> {
                     field: "vp_on",
                     value: PropValue::BoolToggle {
                         field: "vp_on",
-                        value: vp.status.is_on,
+                        value: vp.is_on(),
                     },
                 },
                 ro(
@@ -193,11 +193,14 @@ fn apply_geom_prop(vp: &mut Viewport, field: &str, value: &str) {
             return;
         }
         "vp_on" => {
-            vp.status.is_on = if value == "toggle" {
-                !vp.status.is_on
+            // turn_on/turn_off keep the explicit-off bit in step, so a
+            // viewport the file marked off can be turned back on.
+            let on = if value == "toggle" { !vp.is_on() } else { value == "true" };
+            if on {
+                vp.turn_on();
             } else {
-                value == "true"
-            };
+                vp.turn_off();
+            }
             return;
         }
         "vp_perspective" => {
diff --git a/src/io/mod.rs b/src/io/mod.rs
index 0ad3565bc..7ba12b2c0 100644
--- a/src/io/mod.rs
+++ b/src/io/mod.rs
@@ -2539,7 +2539,7 @@ fn fix_viewport_status_flags(doc: &mut CadDocument) {
             // If bit 0 is not set but bit 15 is, this is an external-format viewport:
             // treat bit 15 as "on" and bit 14 as "locked".
             if (bits & 0x0001) == 0 && (bits & 0x8000) != 0 {
-                vp.status.is_on = true;
+                vp.turn_on();
                 vp.status.locked = (bits & 0x4000) != 0;
             }
         }
diff --git a/src/scene/mod.rs b/src/scene/mod.rs
index 2949edd90..bb92874c9 100644
--- a/src/scene/mod.rs
+++ b/src/scene/mod.rs
@@ -7504,7 +7504,7 @@ impl Scene {
             let Some(EntityType::Viewport(viewport)) = self.document.get_entity(handle) else {
                 continue;
             };
-            if viewport.common.owner_handle != paper_block || !viewport.status.is_on {
+            if viewport.common.owner_handle != paper_block || !viewport.is_on() {
                 continue;
             }
             let mode = render_mode_override.unwrap_or(viewport.render_mode);
diff --git a/src/scene/model/sweep_command_model.rs b/src/scene/model/sweep_command_model.rs
index babc1824a..5d68a3994 100644
--- a/src/scene/model/sweep_command_model.rs
+++ b/src/scene/model/sweep_command_model.rs
@@ -475,8 +475,10 @@ pub fn assoc_edge_curve(entity: &EntityType) -> Option<(i32, codec::objects::Ass
         EntityType::Arc(value) => {
             let normal = glam::DVec3::new(value.normal.x, value.normal.y, value.normal.z).try_normalize()?;
             let axis = arbitrary_x(normal);
-            let mut end = value.end_angle;
-            while end <= value.start_angle { end += std::f64::consts::TAU; }
+            // The end past the start by the arc's sweep; an equal pair is a
+            // full turn. (A loop adding TAU never ends on a huge angle.)
+            let sweep = (value.end_angle - value.start_angle).rem_euclid(std::f64::consts::TAU);
+            let end = value.start_angle + if sweep > 0.0 { sweep } else { std::f64::consts::TAU };
             Some((11, K::Arc, arc(glam::DVec3::new(value.center.x, value.center.y, value.center.z), normal, axis, value.radius, value.start_angle, end)))
         }
         EntityType::LwPolyline(polyline) => {
diff --git a/src/scene/model/sweep_model.rs b/src/scene/model/sweep_model.rs
index dcdc21641..fb5f12072 100644
--- a/src/scene/model/sweep_model.rs
+++ b/src/scene/model/sweep_model.rs
@@ -13,7 +13,7 @@ use codec::EntityType;
 
 use crate::entities::curve::entity_curve;
 pub use super::sweep_command_model::{
-    is_sweep_path, is_sweep_profile, scaled_sweep_path_refusal, spatial_profile, spatial_sweep_record, surface_sweep_record, sweep_expressions, link_sweep_expressions, link_sweep_sources, sweep_sources, resweep_from_sources, surface_associativity, set_surface_associativity, assoc_edge_curve, sweep_record, sweep_refusal_code, sweep_selection_options, swept_surface_entity, swept_with_options,
+    is_sweep_path, is_sweep_profile, scaled_sweep_path_refusal, spatial_profile, spatial_sweep_record, surface_sweep_record, sweep_expressions, link_sweep_expressions, link_sweep_sources, sweep_sources, SWEEP_SOURCES_APP, resweep_from_sources, surface_associativity, set_surface_associativity, assoc_edge_curve, sweep_record, sweep_refusal_code, sweep_selection_options, swept_surface_entity, swept_with_options,
 };
 
 /// A drawn profile, as the kernel wants it: the plane it lies in and the
diff --git a/src/scene/modify.rs b/src/scene/modify.rs
index 23d798a0b..dbde57ece 100644
--- a/src/scene/modify.rs
+++ b/src/scene/modify.rs
@@ -1140,8 +1140,13 @@ impl Scene {
             .filter(|(_, kind)| !matches!(kind, crate::scene::ChangeKind::Removed))
             .map(|(handle, _)| *handle)
             .collect::<rustc_hash::FxHashSet<_>>();
-        if changed.is_empty() { return Vec::new(); }
+        // Every edit passes through here: a drawing with no associative
+        // swept surface (no application registered for them) skips the scan.
+        if changed.is_empty() || !self.document.app_ids.contains(sweep_model::SWEEP_SOURCES_APP) {
+            return Vec::new();
+        }
         let linked = self.document.entities()
+            .filter(|entity| matches!(entity, EntityType::Surface(_)))
             .filter_map(|entity| {
                 let handle = entity.common().handle;
                 let (profile, path) = sweep_model::sweep_sources(entity)?;
diff --git a/src/scene/mspace.rs b/src/scene/mspace.rs
index 2d4a0b305..de7e10b5a 100644
--- a/src/scene/mspace.rs
+++ b/src/scene/mspace.rs
@@ -801,7 +801,7 @@ impl Scene {
                 let Some(EntityType::Viewport(vp)) = self.document.get_entity(*handle) else {
                     return None;
                 };
-                if !vp.status.is_on {
+                if !vp.is_on() {
                     return None;
                 }
                 let rect = self.viewport_screen_rect(vp.common.handle, canvas)?;
@@ -838,7 +838,7 @@ impl Scene {
     pub fn viewport_displays_content(&self, vp_handle: Handle) -> bool {
         matches!(
             self.document.get_entity(vp_handle),
-            Some(EntityType::Viewport(vp)) if vp.status.is_on
+            Some(EntityType::Viewport(vp)) if vp.is_on()
         )
     }
 
@@ -850,7 +850,7 @@ impl Scene {
             let Some(EntityType::Viewport(vp)) = self.document.get_entity(*handle) else {
                 return None;
             };
-            if vp.status.is_on {
+            if vp.is_on() {
                 Some(vp.common.handle)
             } else {
                 None
diff --git a/src/scene/paper.rs b/src/scene/paper.rs
index 11aa7b34d..669d6f74c 100644
--- a/src/scene/paper.rs
+++ b/src/scene/paper.rs
@@ -194,7 +194,7 @@ impl Scene {
             let Some(EntityType::Viewport(vp)) = self.document.get_entity(handle) else {
                 continue;
             };
-            if !vp.status.is_on
+            if !vp.is_on()
                 || self.entity_temporarily_hidden(handle)
             {
                 continue;
diff --git a/src/scene/project.rs b/src/scene/project.rs
index 765c6169a..0cf433927 100644
--- a/src/scene/project.rs
+++ b/src/scene/project.rs
@@ -21,7 +21,7 @@ impl Scene {
             })
             .filter(|vp| {
                 vp.common.owner_handle == paper_block
-                    && vp.status.is_on
+                    && vp.is_on()
                     && only_vp.map_or(true, |h| vp.common.handle == h)
                     && exclude_vp.map_or(true, |h| vp.common.handle != h)
             })
@@ -439,7 +439,7 @@ impl Scene {
             .iter()
             .filter_map(|handle| match self.document.get_entity(*handle) {
                 Some(EntityType::Viewport(viewport))
-                    if viewport.common.owner_handle == paper_block && viewport.status.is_on =>
+                    if viewport.common.owner_handle == paper_block && viewport.is_on() =>
                 {
                     Some(viewport)
                 }