diff --git a/Cargo.lock b/Cargo.lock
index eccd52d11..3e15e16fc 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4361,7 +4361,7 @@ dependencies = [
 [[package]]
 name = "opencadcodec"
 version = "0.6.0"
-source = "git+https://github.com/HakanSeven12/opencadcodec.git?rev=f48d673#f48d6739019b470c5b530d76ac873ffc43f7d311"
+source = "git+https://github.com/HakanSeven12/opencadcodec.git?rev=d57097c#d57097c05c386380d56b97f6b5f396bafa1612ae"
 dependencies = [
  "anyhow",
  "bitflags 2.13.1",
@@ -4384,7 +4384,7 @@ dependencies = [
 [[package]]
 name = "opencadgraph"
 version = "0.1.0"
-source = "git+https://github.com/HakanSeven12/opencadgraph.git?rev=a9ca185#a9ca185e1658243de2f0e19406f966c1d0150eb5"
+source = "git+https://github.com/HakanSeven12/opencadgraph.git?rev=2360341#2360341dd4a159ee2294af62ab527263fb8dc9b4"
 dependencies = [
  "opencadkernel",
  "serde_json",
@@ -4393,7 +4393,7 @@ dependencies = [
 [[package]]
 name = "opencadkernel"
 version = "0.1.0"
-source = "git+https://github.com/HakanSeven12/opencadkernel.git?rev=d8f9b7e#d8f9b7e80c1dc8aeaee7aa0becc9d1ecf2ade5fd"
+source = "git+https://github.com/HakanSeven12/opencadkernel.git?rev=b40fa59#b40fa597ef84c75f06ba00f0e79daff0927b0ca0"
 dependencies = [
  "cavalier_contours",
  "opencadcodec",
@@ -4404,7 +4404,7 @@ dependencies = [
 [[package]]
 name = "opencadkernel-constraints"
 version = "0.1.0"
-source = "git+https://github.com/HakanSeven12/opencadkernel.git?rev=d8f9b7e#d8f9b7e80c1dc8aeaee7aa0becc9d1ecf2ade5fd"
+source = "git+https://github.com/HakanSeven12/opencadkernel.git?rev=b40fa59#b40fa597ef84c75f06ba00f0e79daff0927b0ca0"
 dependencies = [
  "nalgebra",
 ]
diff --git a/Cargo.toml b/Cargo.toml
index 07b816b80..a060b09c7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -37,10 +37,10 @@ rfd = "0.17"
 clap = { version = "4", features = ["derive", "string"] }
 env_logger = "0.11"
 log = "0.4"
-codec = { package = "opencadcodec", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "f48d673", features = ["serde"] }
-kernel = { package = "opencadkernel", git = "https://github.com/HakanSeven12/opencadkernel.git", rev = "d8f9b7e", features = ["acis", "offset"] }
-kernel-constraints = { package = "opencadkernel-constraints", git = "https://github.com/HakanSeven12/opencadkernel.git", rev = "d8f9b7e" }
-graph = { package = "opencadgraph", git = "https://github.com/HakanSeven12/opencadgraph.git", rev = "a9ca185" }
+codec = { package = "opencadcodec", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "d57097c", features = ["serde"] }
+kernel = { package = "opencadkernel", git = "https://github.com/HakanSeven12/opencadkernel.git", rev = "b40fa59", features = ["acis", "offset"] }
+kernel-constraints = { package = "opencadkernel-constraints", git = "https://github.com/HakanSeven12/opencadkernel.git", rev = "b40fa59" }
+graph = { package = "opencadgraph", git = "https://github.com/HakanSeven12/opencadgraph.git", rev = "2360341" }
 dwg-thumbnailer = { path = "crates/dwg-thumbnailer" }
 # Shared SAVE serialization dispatch + web-worker wire format: one
 # implementation for the inline (fallback/native) path and the worker path.
diff --git a/crates/ocs_plugin_api/Cargo.toml b/crates/ocs_plugin_api/Cargo.toml
index 4b653eb36..a1ad2e2f7 100644
--- a/crates/ocs_plugin_api/Cargo.toml
+++ b/crates/ocs_plugin_api/Cargo.toml
@@ -15,7 +15,7 @@ serde_json = { version = "1", optional = true }
 # Pulled in only by the `host` feature, which adds the `opencadcodec`-typed
 # `HostApi` runtime surface. The default crate stays dependency-free so engine
 # crates and external tooling can depend on the manifest/ribbon contract cheaply.
-codec = { package = "opencadcodec", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "f48d673", optional = true, features = ["serde"] }
+codec = { package = "opencadcodec", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "d57097c", optional = true, features = ["serde"] }
 
 # Runtime IPC and serialization (host feature only).
 interprocess = { version = "2", optional = true }
@@ -39,7 +39,7 @@ serde_json = "1"
 serde = { version = "1", features = ["derive"] }
 cargo-lock = "11"
 # opencadcodec is scanned at build time to generate the embedded type registry.
-codec = { package = "opencadcodec", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "f48d673", features = ["serde"] }
+codec = { package = "opencadcodec", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "d57097c", features = ["serde"] }
 
 [dev-dependencies]
 serde_json = "1"
diff --git a/crates/ocs_save/Cargo.toml b/crates/ocs_save/Cargo.toml
index d9684d163..bfa178bff 100644
--- a/crates/ocs_save/Cargo.toml
+++ b/crates/ocs_save/Cargo.toml
@@ -10,6 +10,6 @@ publish = false
 # exactly one implementation. No UI/app dependencies — only the codec + serde.
 
 [dependencies]
-codec = { package = "opencadcodec", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "f48d673", features = ["serde"] }
+codec = { package = "opencadcodec", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "d57097c", features = ["serde"] }
 bincode = "1.3"
 serde = { version = "1", features = ["derive"] }
diff --git a/crates/ocs_web_worker/Cargo.toml b/crates/ocs_web_worker/Cargo.toml
index 1818412b8..13ff4552a 100644
--- a/crates/ocs_web_worker/Cargo.toml
+++ b/crates/ocs_web_worker/Cargo.toml
@@ -8,7 +8,7 @@ publish = false
 crate-type = ["cdylib"]
 
 [dependencies]
-codec = { package = "opencadcodec", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "f48d673", features = ["serde"] }
+codec = { package = "opencadcodec", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "d57097c", features = ["serde"] }
 bincode = "1.3"
 serde = { version = "1", features = ["derive"] }
 console_error_panic_hook = "0.1"
diff --git a/plugins/opencad-python/Cargo.lock b/plugins/opencad-python/Cargo.lock
index ae9c71e96..5a9e11916 100644
--- a/plugins/opencad-python/Cargo.lock
+++ b/plugins/opencad-python/Cargo.lock
@@ -1264,7 +1264,7 @@ dependencies = [
 [[package]]
 name = "opencadcodec"
 version = "0.6.0"
-source = "git+https://github.com/HakanSeven12/opencadcodec.git?rev=f48d673#f48d6739019b470c5b530d76ac873ffc43f7d311"
+source = "git+https://github.com/HakanSeven12/opencadcodec.git?rev=d57097c#d57097c05c386380d56b97f6b5f396bafa1612ae"
 dependencies = [
  "anyhow",
  "bitflags",
diff --git a/src/app/update/file.rs b/src/app/update/file.rs
index c4cd4b69c..94f571b71 100644
--- a/src/app/update/file.rs
+++ b/src/app/update/file.rs
@@ -2196,6 +2196,12 @@ impl OpenCADStudio {
             self.tabs[i].scene.load_current_layout_state();
             self.tabs[i].refresh_active_ucs();
         }
+        // A layout saved with a model viewport entered reopens inside it,
+        // with that viewport's UCS (#1670).
+        let enter_viewport_task = self.tabs[i]
+            .scene
+            .saved_entered_viewport()
+            .map_or_else(Task::none, |handle| Task::done(Message::EnterViewport(handle)));
 
         // The tab may have been reused for the newly opened file. Any Plot
         // dialog cache belongs to the previous/startup drawing and must not
@@ -2317,6 +2323,7 @@ impl OpenCADStudio {
             interaction_task,
             startup_script_task,
             sheet_set_task,
+            enter_viewport_task,
         ])
     }
 
@@ -2640,6 +2647,7 @@ impl OpenCADStudio {
         if self.tabs[i].active_block_edit.is_none() {
             self.tabs[i].scene.sync_camera_to_document();
             self.tabs[i].last_synced_camera_gen = self.tabs[i].scene.camera_generation;
+            self.tabs[i].scene.sync_active_viewport_to_document();
         }
     }
 
diff --git a/src/scene/mod.rs b/src/scene/mod.rs
index 208296bb7..3a137a715 100644
--- a/src/scene/mod.rs
+++ b/src/scene/mod.rs
@@ -4661,6 +4661,46 @@ impl Scene {
         crate::io::set_saved_active_layout(&mut self.document, &self.current_layout);
     }
 
+    /// Record the entered viewport (or the sheet, in paper space) as the
+    /// current layout's last active viewport, which reopens it (#1670).
+    pub fn sync_active_viewport_to_document(&mut self) {
+        let Some(handle) = self.current_layout_object_handle() else {
+            return;
+        };
+        let sheet = match self.document.objects.get(&handle) {
+            Some(ObjectType::Layout(layout)) => {
+                Self::layout_sheet_viewport_handle(&self.document, layout)
+            }
+            _ => return,
+        };
+        let active = self.active_viewport.unwrap_or(sheet);
+        if let Some(ObjectType::Layout(layout)) = self.document.objects.get_mut(&handle) {
+            layout.viewport = active;
+        }
+    }
+
+    /// The model viewport the current layout was saved with entered: its
+    /// last active viewport when that is an on viewport other than the sheet.
+    pub fn saved_entered_viewport(&self) -> Option<Handle> {
+        let handle = self.current_layout_object_handle()?;
+        let Some(ObjectType::Layout(layout)) = self.document.objects.get(&handle) else {
+            return None;
+        };
+        let viewport = layout.viewport;
+        let sheet = Self::layout_sheet_viewport_handle(&self.document, layout);
+        if viewport.is_null() || viewport == sheet {
+            return None;
+        }
+        match self.document.get_entity(viewport) {
+            Some(EntityType::Viewport(vp))
+                if vp.common.owner_handle == layout.block_record && !vp.status.is_off =>
+            {
+                Some(viewport)
+            }
+            _ => None,
+        }
+    }
+
     pub(crate) fn layout_sheet_viewport_handle(
         document: &codec::CadDocument,
         layout: &codec::objects::Layout,
diff --git a/tests/active_space_roundtrip.rs b/tests/active_space_roundtrip.rs
index 7387be1ec..85739c387 100644
--- a/tests/active_space_roundtrip.rs
+++ b/tests/active_space_roundtrip.rs
@@ -77,3 +77,44 @@ fn ctab_is_created_when_absent_then_updated_in_place() {
         Some("Layout3")
     );
 }
+
+/// A layout saved with a model viewport entered reopens inside it; saved
+/// from paper space it reopens on the sheet (#1670).
+#[test]
+fn entered_viewport_survives_a_save_and_reload() {
+    use codec::{entities::Viewport, EntityType};
+    for format in ["dxf", "dwg"] {
+        let mut scene = Scene::new();
+        scene.set_current_layout("Layout1".to_string());
+        let mut sheet = Viewport::new();
+        sheet.id = 1;
+        sheet.width = 420.0;
+        sheet.height = 297.0;
+        let sheet = scene.add_entity(EntityType::Viewport(sheet));
+        let mut model = Viewport::new();
+        model.id = 2;
+        model.width = 100.0;
+        model.height = 80.0;
+        model.view_height = 80.0;
+        let model = scene.add_entity(EntityType::Viewport(model));
+        assert_ne!(sheet, model);
+
+        for entered in [Some(model), None] {
+            scene.active_viewport = entered;
+            scene.sync_active_viewport_to_document();
+            let bytes =
+                OpenCADStudio::io::save_to_bytes(&scene.document, format, scene.document.version)
+                    .expect("save");
+            let doc = OpenCADStudio::io::load_bytes(&format!("roundtrip.{format}"), bytes)
+                .expect("reload");
+            let mut reopened = Scene::new();
+            reopened.document = doc;
+            reopened.current_layout = "Layout1".to_string();
+            assert_eq!(
+                reopened.saved_entered_viewport().is_some(),
+                entered.is_some(),
+                "{format}: entered {entered:?}"
+            );
+        }
+    }
+}