diff --git a/crates/host/src/lib.rs b/crates/host/src/lib.rs
index 577492a53..08e1616a7 100644
--- a/crates/host/src/lib.rs
+++ b/crates/host/src/lib.rs
@@ -106,552 +106,4 @@ pub fn config_dir() -> Option<std::path::PathBuf> {
 }
 
 #[cfg(test)]
-mod tests {
-    use serde_json::json;
-
-    #[test]
-    fn host_runs_tasks_scheduled_by_panel_handlers() {
-        let mut s = super::session();
-        let result = s.execute("script.run", json!({"code": "var w=new Window('palette','Timer regression'); var b=w.add('button',undefined,'Import'); b.onClick=function(){app.scheduleTask(\"app.project.items.addComp('Scheduled',64,64,1,1,25)\",0,false);};w.show();"})).unwrap();
-        assert_eq!(result["ok"], true, "{result}");
-        s.execute("scriptui.click", json!({"window":"Timer regression","widget":"Import"})).unwrap();
-        assert!(s.project.items.is_empty());
-        let tick = s.execute("script.runTasks", json!({})).unwrap();
-        assert_eq!(tick["ran"], 1, "{tick}");
-        assert_eq!(tick["errors"], json!([]), "{tick}");
-        assert!(s.project.items.values().any(|item| item.name == "Scheduled"));
-        s.execute("scriptui.close", json!({"window":"Timer regression"})).unwrap();
-    }
-
-    /// Layer ▸ Camera ▸ Link Focus Distance to Point of Interest / to Layer: the expressions
-    /// evaluate to the camera's focus on the target.
-    #[test]
-    fn focus_link_expressions_track_the_target() {
-        use effectcraft_engine::geom::vec3;
-        let mut s = super::session();
-        s.execute("comp.new", json!({"name": "F", "width": 400, "height": 300, "duration": 2})).unwrap();
-        let t = s.execute("layer.newSolid", json!({"color": "#ffffff", "width": 50, "height": 50})).unwrap()["layer"].as_u64().unwrap();
-        s.execute("layer.setSwitch", json!({"layers": [t], "switch": "threeD", "value": true})).unwrap();
-        s.execute("layer.setTransform", json!({"layer": t, "prop": "position", "value": [260, 120, 400]})).unwrap();
-        let cam = s.execute("layer.newCamera", json!({})).unwrap()["layer"].as_u64().unwrap();
-        let cid = s.active_comp_id().unwrap();
-        let focus = |s: &effectcraft_engine::Session| {
-            let comp = s.project.comp(cid).unwrap();
-            let mut ctx = effectcraft_engine::render::EvalCtx::new(&s.project, cid, comp, s.time());
-            ctx.expr = s.expr.as_deref();
-            let l = comp.layer(effectcraft_engine::project::LayerId(cam)).unwrap();
-            ctx.value(l, l.props.prop("cameraOptions/focusDistance").unwrap()).as_f64()
-        };
-        let depth = |s: &effectcraft_engine::Session| {
-            let comp = s.project.comp(cid).unwrap();
-            let ctx = effectcraft_engine::render::EvalCtx::new(&s.project, cid, comp, s.time());
-            let c = comp.layer(effectcraft_engine::project::LayerId(cam)).unwrap();
-            let tl = comp.layer(effectcraft_engine::project::LayerId(t)).unwrap();
-            let cs = effectcraft_engine::render::three_d::camera::layer_camera(&ctx, c);
-            cs.depth(ctx.world_matrix(tl).apply(vec3(25.0, 25.0, 0.0)))
-        };
-        s.execute("layer.select", json!({"layers": [cam, t]})).unwrap();
-        let set = s.execute("camera.setFocusToLayer", json!({})).unwrap()["focusDistance"].as_f64().unwrap();
-        assert!((set - depth(&s)).abs() < 1e-6 && (focus(&s) - set).abs() < 1e-6);
-        s.execute("camera.linkFocusToLayer", json!({})).unwrap();
-        // Move the target: the linked focus follows.
-        s.execute("layer.setTransform", json!({"layer": t, "prop": "position", "value": [200, 150, 900]})).unwrap();
-        assert!((focus(&s) - depth(&s)).abs() < 1e-3, "{} vs {}", focus(&s), depth(&s));
-        s.execute("camera.linkFocusToPoi", json!({"camera": cam})).unwrap();
-        let poi = {
-            let l = s.active_comp().unwrap().layer(effectcraft_engine::project::LayerId(cam)).unwrap();
-            let p = l.props.prop("transform/position").unwrap().value.as_vec3();
-            let q = l.props.prop("transform/poi").unwrap().value.as_vec3();
-            ((p[0] - q[0]).powi(2) + (p[1] - q[1]).powi(2) + (p[2] - q[2]).powi(2)).sqrt()
-        };
-        assert!((focus(&s) - poi).abs() < 1e-6, "{} vs {poi}", focus(&s));
-    }
-
-    #[test]
-    fn wired_session_renders_demo_with_expressions() {
-        let mut s = super::session();
-        s.execute("file.openDemoProject", json!({})).unwrap();
-        let cid = s.active_comp_id().unwrap();
-        let lid = s.active_comp().unwrap().layers[1].id.0;
-        s.execute("prop.setExpression", json!({"layer": lid, "path": "transform/rotation", "expression": "time * 90"})).unwrap();
-        let img = s.render(cid, s.time(), effectcraft_engine::render::RenderOpts { scale: 0.25, ..Default::default() });
-        assert!(img.data.iter().any(|p| p[3] > 0.5));
-    }
-
-    /// File ▸ Import of glTF/GLB/OBJ models through the media layer, placed as model layers and
-    /// drawn by the Advanced 3D renderer.
-    #[test]
-    fn imported_models_render_in_advanced_3d() {
-        let fx = |n: &str| format!("{}/../model/tests/fixtures/{n}", env!("CARGO_MANIFEST_DIR"));
-        let mut s = super::session();
-        s.execute("comp.new", json!({"name": "M", "width": 160, "height": 120, "renderer": "advanced3d"})).unwrap();
-        let r = s.execute("file.import", json!({"paths": [fx("cube.obj"), fx("quad.glb"), fx("quad.gltf")]})).unwrap();
-        assert_eq!(r["errors"], json!([]), "{r}");
-        let items: Vec<u64> = r["items"].as_array().unwrap().iter().map(|v| v.as_u64().unwrap()).collect();
-        assert_eq!(items.len(), 3);
-        let cube = s.execute("layer.addItem", json!({"item": items[0]})).unwrap()["layer"].as_u64().unwrap();
-        s.execute("prop.set", json!({"layer": cube, "path": "transform/rotationY", "value": 30})).unwrap();
-        s.execute("prop.set", json!({"layer": cube, "path": "transform/rotationX", "value": 20})).unwrap();
-        let cid = s.active_comp_id().unwrap();
-        let opts = effectcraft_engine::render::RenderOpts::default();
-        let img = s.render(cid, s.time(), opts);
-        let covered = img.data.iter().filter(|p| p[3] > 0.99).count();
-        assert!(covered > 1000, "the cube covers part of the frame: {covered}");
-        // Red faces (material Red) are visible.
-        assert!(img.data.iter().any(|p| p[3] > 0.99 && p[0] > 0.5 && p[1] < 0.2));
-        // The textured binary glTF quad.
-        for _ in 0..3 {
-            s.execute("edit.undo", json!({})).unwrap();
-        }
-        s.execute("layer.addItem", json!({"item": items[1]})).unwrap();
-        let img = s.render(cid, s.time(), opts);
-        assert!(img.data.iter().filter(|p| p[3] > 0.99).count() > 1000);
-        // Classic 3D doesn't draw models.
-        s.execute("comp.renderer", json!({"renderer": "classic3d"})).unwrap();
-        assert!(s.render(cid, s.time(), opts).data.iter().all(|p| p[3] == 0.0));
-    }
-
-    /// A binary glTF of a red cube 2 units wide (positions and indices only).
-    fn glb_cube() -> Vec<u8> {
-        let mut bin: Vec<u8> = (0..8u32).flat_map(|i| [i & 1, (i >> 1) & 1, (i >> 2) & 1].map(|b| b as f32 * 2.0 - 1.0)).flat_map(f32::to_le_bytes).collect();
-        let faces: [[u16; 4]; 6] = [[0, 2, 3, 1], [4, 5, 7, 6], [0, 1, 5, 4], [2, 6, 7, 3], [0, 4, 6, 2], [1, 3, 7, 5]];
-        bin.extend(faces.iter().flat_map(|f| [f[0], f[1], f[2], f[0], f[2], f[3]]).flat_map(u16::to_le_bytes));
-        let gltf = json!({
-            "asset": {"version": "2.0"},
-            "scene": 0,
-            "scenes": [{"nodes": [0]}],
-            "nodes": [{"mesh": 0}],
-            "meshes": [{"primitives": [{"attributes": {"POSITION": 0}, "indices": 1, "material": 0}]}],
-            "materials": [{"pbrMetallicRoughness": {"baseColorFactor": [1, 0, 0, 1], "metallicFactor": 0, "roughnessFactor": 1}}],
-            "buffers": [{"byteLength": bin.len()}],
-            "bufferViews": [{"buffer": 0, "byteOffset": 0, "byteLength": 96}, {"buffer": 0, "byteOffset": 96, "byteLength": 72}],
-            "accessors": [
-                {"bufferView": 0, "componentType": 5126, "count": 8, "type": "VEC3", "min": [-1, -1, -1], "max": [1, 1, 1]},
-                {"bufferView": 1, "componentType": 5123, "count": 36, "type": "SCALAR"}
-            ]
-        });
-        let mut text = gltf.to_string().into_bytes();
-        text.resize(text.len().div_ceil(4) * 4, b' ');
-        let chunk = |kind: &[u8; 4], data: &[u8]| [&(data.len() as u32).to_le_bytes()[..], kind, data].concat();
-        let body = [chunk(b"JSON", &text), chunk(b"BIN\0", &bin)].concat();
-        [&b"glTF"[..], &2u32.to_le_bytes(), &(12 + body.len() as u32).to_le_bytes(), &body].concat()
-    }
-
-    /// #264: a model imported into a new composition (Classic 3D by default) was invisible on
-    /// every renderer, because only Advanced 3D draws models. Adding it now switches the comp,
-    /// and the software renderer (no GPU, as on the reporter's Intel HD Graphics 5500) draws it.
-    #[test]
-    fn imported_glb_shows_in_a_new_composition() {
-        let path = std::env::temp_dir().join(format!("effectcraft-264-cube-{}.glb", std::process::id()));
-        std::fs::write(&path, glb_cube()).unwrap();
-        let mut s = super::session();
-        assert!(s.accel.is_none(), "renders in software");
-        let r = s.execute("file.import", json!({"paths": [path.to_string_lossy()]})).unwrap();
-        assert_eq!(r["errors"], json!([]), "{r}");
-        s.state.project_selection = vec![effectcraft_project::ItemId(r["items"][0].as_u64().unwrap())];
-        s.execute("file.newCompFromSelection", json!({})).unwrap();
-        let comp = s.active_comp().unwrap();
-        assert_eq!(comp.renderer, effectcraft_project::Renderer::Advanced3D);
-        let layer = comp.layers[0].id.0;
-        s.execute("prop.set", json!({"layer": layer, "path": "transform/rotationY", "value": 30})).unwrap();
-        s.execute("prop.set", json!({"layer": layer, "path": "transform/rotationX", "value": 20})).unwrap();
-        let cid = s.active_comp_id().unwrap();
-        let img = s.render(cid, s.time(), effectcraft_engine::render::RenderOpts { scale: 0.25, ..Default::default() });
-        let red = img.data.iter().filter(|p| p[3] > 0.99 && p[0] > 0.2 && p[1] < 0.05 && p[2] < 0.05).count();
-        let _ = std::fs::remove_file(&path);
-        // Half the comp height wide, seen at an angle: well over 5% of the frame.
-        assert!(red * 20 > img.data.len(), "red cube pixels: {red} of {}", img.data.len());
-    }
-
-    /// #651: an animated GIF imported from disk plays: the layer shows each frame at its time,
-    /// in the viewer's renders and in exports alike.
-    #[test]
-    fn an_imported_animated_gif_plays() {
-        let dir = std::env::temp_dir().join(format!("ec-gif-{}", std::process::id()));
-        std::fs::create_dir_all(&dir).unwrap();
-        let path = dir.join("anim.gif");
-        let mut bytes = Vec::new();
-        {
-            let mut enc = gif::Encoder::new(&mut bytes, 4, 4, &[]).unwrap();
-            for rgb in [[255u8, 0, 0], [0, 255, 0], [0, 0, 255]] {
-                let mut f = gif::Frame::from_rgb(4, 4, &rgb.repeat(16));
-                f.delay = 10;
-                enc.write_frame(&f).unwrap();
-            }
-        }
-        std::fs::write(&path, bytes).unwrap();
-        let mut s = super::session();
-        s.execute("comp.new", json!({"name": "G", "width": 4, "height": 4, "frameRate": 30, "duration": 1})).unwrap();
-        s.execute("file.import", json!({"paths": [path.to_string_lossy()], "addToComp": true})).unwrap();
-        let cid = s.active_comp_id().unwrap();
-        let rgb = |t: f64| {
-            let img = s.render(cid, effectcraft_time::Tick::from_seconds_f64(t), effectcraft_engine::render::RenderOpts::default());
-            let p = img.data[5];
-            [p[0].round(), p[1].round(), p[2].round()]
-        };
-        assert_eq!(rgb(0.05), [1.0, 0.0, 0.0]);
-        assert_eq!(rgb(0.15), [0.0, 1.0, 0.0]);
-        assert_eq!(rgb(0.25), [0.0, 0.0, 1.0]);
-        let _ = std::fs::remove_dir_all(dir);
-    }
-
-    /// The web app's path: outputs go to a sink (downloads), never to the file system.
-    #[test]
-    fn render_queue_exports_to_a_sink() {
-        use std::sync::{Arc, Mutex};
-        let got: Arc<Mutex<Vec<(String, Vec<u8>)>>> = Arc::default();
-        let g = got.clone();
-        let mut s = super::session();
-        s.exporter = Some(Arc::new(super::FileExporter { sink: Some(Arc::new(move |p: &str, d: Vec<u8>| g.lock().unwrap().push((p.to_string(), d)))) }));
-        s.execute("file.openDemoProject", json!({})).unwrap();
-        // Rooted without a drive letter is not absolute on Windows, where the engine joins it to the home drive.
-        let dir = if cfg!(windows) { "C:/no-such-dir-effectcraft-sink-test" } else { "/no-such-dir-effectcraft-sink-test" };
-        s.execute(
-            "renderQueue.add",
-            json!({"format": "gif", "output": format!("{dir}/a.gif"), "resolution": 0.0625, "timeSpan": "custom", "start": 0.0, "end": 0.2}),
-        )
-        .unwrap();
-        s.execute(
-            "renderQueue.add",
-            json!({"format": "png", "output": format!("{dir}/seq_[##].png"), "resolution": 0.0625, "timeSpan": "custom", "start": 0.0, "end": 0.1}),
-        )
-        .unwrap();
-        s.execute("renderQueue.render", json!({"wait": true})).unwrap();
-        s.poll_render();
-        let mut got = got.lock().unwrap().clone();
-        got.sort_by(|a, b| a.0.cmp(&b.0));
-        let names: Vec<std::path::PathBuf> = got.iter().map(|(p, _)| std::path::PathBuf::from(p)).collect();
-        let expected = [format!("{dir}/a.gif"), format!("{dir}/seq_00.png"), format!("{dir}/seq_01.png"), format!("{dir}/seq_02.png")]
-            .map(|p| std::path::absolute(p).unwrap());
-        assert_eq!(names, expected);
-        assert!(got[0].1.starts_with(b"GIF89a"));
-        assert!(got[1].1.starts_with(b"\x89PNG"));
-        assert!(!std::path::Path::new(dir).exists());
-    }
-
-    #[test]
-    fn render_queue_exports_demo_comp() {
-        let dir = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../../target/test-out/host-rq");
-        let _ = std::fs::remove_dir_all(&dir);
-        let mut s = super::session();
-        s.execute("file.openDemoProject", json!({})).unwrap();
-        let out = dir.join("[compName]_[width]x[height].[fileExtension]");
-        let r = s
-            .execute(
-                "renderQueue.add",
-                json!({"format": "h264", "output": out.to_string_lossy(), "resolution": 0.125, "timeSpan": "custom", "start": 0.0, "end": 0.4}),
-            )
-            .unwrap();
-        let path = r["outputPath"].as_str().unwrap().to_string();
-        assert!(path.ends_with("_240x134.mp4"), "{path}");
-        // A second item: PNG sequence, rendered in the background.
-        s.execute("renderQueue.add", json!({"format": "png", "output": dir.join("seq_[###].png").to_string_lossy(), "resolution": 0.0625, "timeSpan": "custom", "start": 0.0, "end": 0.2})).unwrap();
-        let r = s.execute("renderQueue.render", json!({"wait": false})).unwrap();
-        assert_eq!(r["items"].as_array().unwrap().len(), 2);
-        let t0 = std::time::Instant::now();
-        while s.is_rendering() {
-            assert!(t0.elapsed().as_secs() < 300, "render timed out");
-            std::thread::sleep(std::time::Duration::from_millis(20));
-            s.poll_render();
-        }
-        s.poll_render();
-        let list = s.execute("renderQueue.list", json!({})).unwrap();
-        for it in list["items"].as_array().unwrap() {
-            assert_eq!(it["statusLabel"], "Done", "{it}");
-            assert!(it["render_time"].as_f64().is_some());
-            assert!(std::path::Path::new(it["last_output"].as_str().unwrap()).exists(), "{it}");
-        }
-        assert!(std::path::Path::new(&path).metadata().unwrap().len() > 500);
-        assert!(dir.join("seq_000.png").exists() && dir.join("seq_005.png").exists() && !dir.join("seq_006.png").exists());
-        // Rendering again needs a re-queue.
-        assert!(s.execute("renderQueue.render", json!({})).is_err());
-        s.execute("renderQueue.setRender", json!({"index": 1, "render": true})).unwrap();
-        assert_eq!(s.project.render_queue[0].status, effectcraft_engine::project::render_queue::RenderStatus::Queued);
-    }
-
-    /// Value of a property of layer `l` at time 0 (keys + expression).
-    fn value(s: &effectcraft_engine::Session, l: u64, path: &str) -> effectcraft_engine::keyframe::Value {
-        let cid = s.active_comp_id().unwrap();
-        let comp = s.project.comp(cid).unwrap();
-        let layer = comp.layer(effectcraft_engine::project::LayerId(l)).unwrap();
-        let ctx =
-            effectcraft_engine::render::EvalCtx { project: &s.project, comp_id: cid, comp, time: Default::default(), expr: s.expr.as_deref(), footage: None };
-        ctx.value(layer, layer.props.prop(path).unwrap())
-    }
-
-    #[test]
-    fn pick_whip_expressions_evaluate() {
-        let mut s = super::session();
-        s.execute("comp.new", json!({"name": "C", "width": 200, "height": 200, "frameRate": 30, "duration": 2})).unwrap();
-        let a = s.execute("layer.newSolid", json!({"color": "#ffffff"})).unwrap()["layer"].as_u64().unwrap();
-        let b = s.execute("layer.newSolid", json!({"name": "Src", "color": "#ff0000"})).unwrap()["layer"].as_u64().unwrap();
-        s.execute("prop.set", json!({"layer": b, "path": "transform/rotation", "value": 33})).unwrap();
-        s.execute("prop.set", json!({"layer": b, "path": "transform/position", "value": [12, 34]})).unwrap();
-        s.execute("effect.apply", json!({"layer": b, "effect": "Gaussian Blur"})).unwrap();
-        s.execute("prop.set", json!({"layer": b, "path": "effects/#1/blurriness", "value": 21})).unwrap();
-        s.execute("layer.addMask", json!({"layer": b})).unwrap();
-        s.execute("prop.set", json!({"layer": b, "path": "masks/#1/feather", "value": [7, 7]})).unwrap();
-        let link = |s: &mut effectcraft_engine::Session, from: &str, to: &str| {
-            s.execute("prop.pickWhip", json!({"layer": a, "path": from, "target": {"layer": b, "path": to}})).unwrap();
-        };
-        link(&mut s, "transform/opacity", "transform/rotation");
-        assert_eq!(value(&s, a, "transform/opacity").as_f64(), 33.0);
-        link(&mut s, "transform/scale", "transform/rotation");
-        let cid = s.active_comp_id().unwrap();
-        let ep = effectcraft_expr::eval_property(&s.project, cid, effectcraft_engine::project::LayerId(a), "transform/scale", 0.0);
-        assert!(ep.is_ok(), "{ep:?}");
-        assert_eq!(value(&s, a, "transform/scale").as_vec2(), [33.0, 33.0]);
-        link(&mut s, "transform/position", "transform/position");
-        assert_eq!(value(&s, a, "transform/position").as_vec2(), [12.0, 34.0]);
-        link(&mut s, "transform/rotation", "effects/#1/blurriness");
-        assert_eq!(value(&s, a, "transform/rotation").as_f64(), 21.0);
-        link(&mut s, "transform/opacity", "masks/#1/feather");
-        assert_eq!(value(&s, a, "transform/opacity").as_f64(), 7.0);
-        // Separated dimensions: X Position reference.
-        s.execute("prop.separateDimensions", json!({"layer": b})).unwrap();
-        link(&mut s, "transform/rotation", "transform/positionX");
-        assert_eq!(value(&s, a, "transform/rotation").as_f64(), 12.0);
-    }
-
-    /// The expression error bar's list: evaluation errors and syntax errors, with the layer and
-    /// property they belong to.
-    #[test]
-    fn expression_errors_are_collected() {
-        let mut s = super::session();
-        s.execute("comp.new", json!({"name": "C", "width": 100, "height": 100, "frameRate": 30, "duration": 2})).unwrap();
-        let a = s.execute("layer.newSolid", json!({"name": "Box", "color": "#ffffff"})).unwrap()["layer"].as_u64().unwrap();
-        s.execute("prop.setExpression", json!({"layer": a, "path": "transform/opacity", "expression": "50"})).unwrap();
-        assert_eq!(s.execute("expr.errors", json!({})).unwrap()["count"], 0);
-        s.execute("prop.setExpression", json!({"layer": a, "path": "transform/rotation", "expression": "thisComp.layer(\"Nope\").rotation"})).unwrap();
-        s.execute("prop.setExpression", json!({"layer": a, "path": "transform/opacity", "expression": "1 +* ("})).unwrap();
-        let r = s.execute("expr.errors", json!({})).unwrap();
-        assert_eq!(r["count"], 2, "{r}");
-        let errs = r["errors"].as_array().unwrap();
-        let rot = errs.iter().find(|e| e["path"] == "transform/rotation").unwrap();
-        assert!(rot["message"].as_str().unwrap().contains("Nope"), "{rot}");
-        assert_eq!(rot["layerIndex"], 1);
-        assert_eq!(rot["layerName"], "Box");
-        assert_eq!(rot["disabled"], false);
-        let op = errs.iter().find(|e| e["path"] == "transform/opacity").unwrap();
-        assert_eq!(op["disabled"], true);
-        assert!(r["text"][0].as_str().unwrap().contains("of layer 1 ('Box') in comp 'C'"), "{r}");
-        // A user-disabled (but valid) expression is not an error.
-        s.execute("prop.setExpression", json!({"layer": a, "path": "transform/rotation", "expression": "45"})).unwrap();
-        s.execute("prop.setExpression", json!({"layer": a, "path": "transform/rotation", "enabled": false})).unwrap();
-        assert_eq!(s.execute("expr.errors", json!({})).unwrap()["count"], 1);
-        // The Expression Language menu is categorised.
-        let m = s.execute("expr.languageMenu", json!({})).unwrap();
-        assert!(m.as_array().unwrap().iter().any(|c| c["category"] == "Footage" && c["items"].as_array().unwrap().iter().any(|i| i["text"] == "sourceData")));
-    }
-
-    /// File ▸ Import of JSON/CSV data files as data footage, read by expressions.
-    #[test]
-    fn imported_data_files_drive_expressions() {
-        let dir = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../../target/test-out/host-data");
-        let _ = std::fs::remove_dir_all(&dir);
-        std::fs::create_dir_all(&dir).unwrap();
-        std::fs::write(dir.join("levels.csv"), "label,value\nlow,10\nhigh,90\n").unwrap();
-        std::fs::write(dir.join("cfg.json"), r#"{"angle": 33}"#).unwrap();
-        std::fs::write(dir.join("broken.json"), "{nope").unwrap();
-        let mut s = super::session();
-        s.execute("comp.new", json!({"name": "C", "width": 100, "height": 100, "frameRate": 30, "duration": 2})).unwrap();
-        let paths: Vec<String> = ["levels.csv", "cfg.json", "broken.json"].iter().map(|n| dir.join(n).to_string_lossy().to_string()).collect();
-        let r = s.execute("file.import", json!({"paths": paths})).unwrap();
-        assert_eq!(r["items"].as_array().unwrap().len(), 2, "{r}");
-        assert_eq!(r["errors"].as_array().unwrap().len(), 1, "{r}");
-        let csv = r["items"][0].as_u64().unwrap();
-        assert_eq!(s.project.item(effectcraft_engine::project::ItemId(csv)).unwrap().type_name(), "Data");
-        assert!(s.execute("layer.addItem", json!({"item": csv})).is_err(), "data files are not layers");
-        let a = s.execute("layer.newSolid", json!({"color": "#ffffff"})).unwrap()["layer"].as_u64().unwrap();
-        s.execute("prop.setExpression", json!({"layer": a, "path": "transform/opacity", "expression": "footage(\"levels.csv\").sourceData[1].value"})).unwrap();
-        s.execute("prop.setExpression", json!({"layer": a, "path": "transform/rotation", "expression": "footage(\"cfg.json\").sourceData.angle"})).unwrap();
-        assert_eq!(value(&s, a, "transform/opacity").as_f64(), 90.0);
-        assert_eq!(value(&s, a, "transform/rotation").as_f64(), 33.0);
-    }
-
-    /// sampleImage through the renderer: a box's Fill colour follows the solid under it.
-    #[test]
-    fn sample_image_drives_a_colour() {
-        let mut s = super::session();
-        s.execute("comp.new", json!({"name": "C", "width": 100, "height": 100, "frameRate": 30, "duration": 2})).unwrap();
-        s.execute("layer.newSolid", json!({"name": "Bg", "color": "#00ff00"})).unwrap();
-        let a = s.execute("layer.newSolid", json!({"name": "Fg", "color": "#ffffff", "width": 20, "height": 20})).unwrap()["layer"].as_u64().unwrap();
-        s.execute("effect.apply", json!({"layer": a, "effect": "Fill"})).unwrap();
-        s.execute(
-            "prop.setExpression",
-            json!({"layer": a, "path": "effects/#1/color", "expression": "thisComp.layer(\"Bg\").sampleImage(thisComp.layer(\"Bg\").fromComp(toComp(anchorPoint)))"}),
-        )
-        .unwrap();
-        let cid = s.active_comp_id().unwrap();
-        let img = s.render(cid, s.time(), effectcraft_engine::render::RenderOpts::default());
-        let px = img.get(50, 50);
-        assert!(px[1] > 0.99 && px[0] < 0.01, "the box is filled with the sampled green: {px:?}");
-    }
-
-    /// Proxies through the real media and export layers: Render Settings ▸ Proxy Use decides
-    /// whether an export uses the proxy, and Create Proxy renders and attaches one.
-    #[test]
-    fn proxies_in_exports_and_create_proxy() {
-        let dir = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../../target/test-out/host-proxy");
-        let _ = std::fs::remove_dir_all(&dir);
-        std::fs::create_dir_all(&dir).unwrap();
-        let p = |n: &str| dir.join(n).to_string_lossy().to_string();
-        let mut s = super::session();
-        // Source and proxy stills, written by the app itself.
-        s.execute("comp.new", json!({"name": "Red", "width": 16, "height": 16, "frameRate": 10, "duration": 1})).unwrap();
-        let red = s.active_comp_id().unwrap();
-        s.execute("layer.newSolid", json!({"color": "#ff0000"})).unwrap();
-        s.execute("comp.saveFrameAs", json!({"path": p("red.png")})).unwrap();
-        s.execute("comp.new", json!({"name": "Blue", "width": 8, "height": 8, "frameRate": 10, "duration": 1})).unwrap();
-        s.execute("layer.newSolid", json!({"color": "#0000ff"})).unwrap();
-        s.execute("comp.saveFrameAs", json!({"path": p("blue.png")})).unwrap();
-        let foot = s.execute("file.import", json!({"paths": [p("red.png")]})).unwrap()["items"][0].as_u64().unwrap();
-        s.execute("file.setProxy", json!({"item": foot, "path": p("blue.png")})).unwrap();
-        s.execute("comp.new", json!({"name": "Out", "width": 16, "height": 16, "frameRate": 10, "duration": 1})).unwrap();
-        let out = s.active_comp_id().unwrap();
-        s.execute("layer.addItem", json!({"item": foot})).unwrap();
-        // Export one frame with each Proxy Use.
-        for (name, using) in [("all", "use_all_[#].png"), ("none", "use_none_[#].png")] {
-            s.execute(
-                "renderQueue.add",
-                json!({"comp": out.0, "format": "png", "output": p(using), "timeSpan": "custom", "start": 0.0, "end": 0.1, "proxyUse": name}),
-            )
-            .unwrap();
-        }
-        s.execute("renderQueue.render", json!({"wait": true})).unwrap();
-        s.poll_render();
-        let centre = |s: &mut effectcraft_engine::Session, path: &str| {
-            let id = s.execute("file.import", json!({"paths": [path]})).unwrap()["items"][0].as_u64().unwrap();
-            s.execute("comp.new", json!({"name": "Probe", "width": 16, "height": 16, "frameRate": 10, "duration": 1})).unwrap();
-            s.execute("layer.addItem", json!({"item": id})).unwrap();
-            let c = s.active_comp_id().unwrap();
-            s.render(c, Default::default(), Default::default()).get(8, 8)
-        };
-        let all = centre(&mut s, &p("use_all_0.png"));
-        assert!(all[2] > 0.99 && all[0] < 0.01, "Use All Proxies renders the blue proxy: {all:?}");
-        let none = centre(&mut s, &p("use_none_0.png"));
-        assert!(none[0] > 0.99 && none[2] < 0.01, "Use No Proxies renders the red source: {none:?}");
-        // Create Proxy ▸ Still: rendered at half size and attached to the comp.
-        s.execute("file.createProxy", json!({"kind": "still", "comp": red.0, "path": p("red_proxy_[#####].png")})).unwrap();
-        s.execute("renderQueue.render", json!({"wait": true})).unwrap();
-        s.poll_render();
-        let px = s.project.item(red).unwrap().proxy.clone().expect("Create Proxy attached the rendered still");
-        assert!(px.enabled);
-        assert_eq!((px.footage.width, px.footage.height), (8, 8));
-        assert!(std::path::Path::new(&px.footage.path).exists(), "{}", px.footage.path);
-    }
-
-    /// A script builds a comp, queues it and renders it through the Render Queue.
-    #[test]
-    fn script_renders_through_the_render_queue() {
-        let dir = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../../target/test-out/host-script");
-        let _ = std::fs::remove_dir_all(&dir);
-        let out = dir.join("scripted.gif");
-        let mut s = super::session();
-        let code = format!(
-            r#"
-            var comp = app.project.items.addComp("Scripted", 64, 48, 1, 0.2, 10);
-            var sq = comp.layers.addSolid([1, 0.5, 0], "Square", 16, 16, 1);
-            sq.transform.position.setValueAtTime(0, [8, 24]);
-            sq.transform.position.setValueAtTime(0.1, [56, 24]);
-            var item = app.project.renderQueue.items.add(comp);
-            item.outputModule(1).applyTemplate("GIF");
-            item.outputModule(1).file = new File({});
-            app.project.renderQueue.render();
-            [item.status == RQItemStatus.DONE, item.outputModule(1).file.fsName, app.project.renderQueue.numItems]
-            "#,
-            serde_json::to_string(&out.to_string_lossy()).unwrap()
-        );
-        let r = s.execute("script.run", json!({"code": code})).unwrap();
-        assert_eq!(r["ok"], json!(true), "{r}");
-        assert_eq!(r["result"][0], json!(true), "{r}");
-        assert_eq!(r["result"][2], json!(1));
-        let bytes = std::fs::read(&out).unwrap();
-        assert!(bytes.starts_with(b"GIF89a"));
-    }
-
-    /// importFile, layers.add(footage) and project save/open from a script.
-    #[test]
-    fn script_imports_footage_and_saves() {
-        let dir = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../../target/test-out/host-script-import");
-        let _ = std::fs::remove_dir_all(&dir);
-        std::fs::create_dir_all(&dir).unwrap();
-        let q = |n: &str| serde_json::to_string(&dir.join(n).to_string_lossy()).unwrap();
-        let mut s = super::session();
-        let code = format!(
-            r#"
-            var c = app.project.items.addComp("Src", 32, 32, 1, 1, 10);
-            c.layers.addSolid([0, 1, 0], "G", 32, 32, 1);
-            app.run("comp.saveFrameAs", {{comp: c.id, path: {png}}});
-            var still = app.project.importFile(new ImportOptions(new File({png})));
-            var main = app.project.items.addComp("Main", 64, 64, 1, 1, 10);
-            var l = main.layers.add(still);
-            app.project.save(new File({proj}));
-            [still instanceof FootageItem, still.width, still.mainSource.isStill, l.source.name, app.project.file.name]
-            "#,
-            png = q("frame.png"),
-            proj = q("p.ecproj")
-        );
-        let r = s.execute("script.run", json!({"code": code})).unwrap();
-        assert_eq!(r["ok"], json!(true), "{r}");
-        assert_eq!(r["result"], json!([true, 32, true, "frame.png", "p.ecproj"]), "{r}");
-        let r = s.execute("script.run", json!({"code": format!("app.open(new File({})); app.project.numItems", q("p.ecproj"))})).unwrap();
-        assert_eq!(r["result"], json!(5), "{r}"); // Src, Solids, G, frame.png, Main
-    }
-
-    #[test]
-    fn expression_syntax_errors_disable_the_expression() {
-        let mut s = super::session();
-        s.execute("comp.new", json!({"name": "C", "width": 100, "height": 100, "frameRate": 30, "duration": 2})).unwrap();
-        let a = s.execute("layer.newSolid", json!({"color": "#ffffff"})).unwrap()["layer"].as_u64().unwrap();
-        let r = s.execute("prop.setExpression", json!({"layer": a, "path": "transform/opacity", "expression": "1 +* ("})).unwrap();
-        assert!(r["error"].is_string(), "{r}");
-        let pr = s.active_comp().unwrap().layers[0].props.prop("transform/opacity").unwrap().clone();
-        assert!(!pr.expr.unwrap().enabled);
-        assert_eq!(value(&s, a, "transform/opacity").as_f64(), 100.0);
-        s.execute("prop.setExpression", json!({"layer": a, "path": "transform/opacity", "expression": "50"})).unwrap();
-        assert_eq!(value(&s, a, "transform/opacity").as_f64(), 50.0);
-    }
-    /// Create Stereo 3D Rig: the eye cameras' expressions follow the master camera and the
-    /// Stereo 3D Controls (and agree with the values the command wrote).
-    #[test]
-    fn stereo_rig_expressions_follow_the_master_camera() {
-        let mut s = super::session();
-        s.execute("comp.new", json!({"name": "Shot", "width": 640, "height": 360, "frameRate": 30, "duration": 2})).unwrap();
-        let src = s.active_comp_id().unwrap();
-        let cam = s.execute("layer.newCamera", json!({"name": "Main", "position": [320, 180, -800], "poi": [320, 180, 0], "zoom": 900})).unwrap()["layer"]
-            .as_u64()
-            .unwrap();
-        let r = s.execute("camera.stereoRig", json!({"sceneDepth": 4})).unwrap();
-        let ctl = r["controls"].as_u64().unwrap();
-        let left = effectcraft_engine::project::ItemId(r["leftComp"].as_u64().unwrap());
-        // The left eye camera's evaluated value (expressions on).
-        let v3 = |s: &effectcraft_engine::Session, path: &str| {
-            let comp = s.project.comp(left).unwrap();
-            let layer = &comp.layers[0];
-            let ctx = effectcraft_engine::render::EvalCtx {
-                project: &s.project,
-                comp_id: left,
-                comp,
-                time: Default::default(),
-                expr: s.expr.as_deref(),
-                footage: None,
-            };
-            ctx.value(layer, layer.props.prop(path).unwrap()).as_vec3()
-        };
-        let close = |a: [f64; 3], b: [f64; 3]| (0..3).all(|i| (a[i] - b[i]).abs() < 1e-6);
-        let d = 0.04 * 640.0;
-        assert!(close(v3(&s, "transform/position"), [320.0 - d / 2.0, 180.0, -800.0]), "{:?}", v3(&s, "transform/position"));
-        assert!(close(v3(&s, "transform/poi"), [320.0 - d / 2.0, 180.0, 0.0]), "{:?}", v3(&s, "transform/poi"));
-        // Moving the master moves the eyes.
-        s.execute("comp.open", json!({"comp": src.0})).unwrap();
-        s.execute("prop.set", json!({"layer": cam, "path": "transform/position", "value": [300, 180, -800]})).unwrap();
-        s.execute("prop.set", json!({"layer": cam, "path": "transform/poi", "value": [300, 180, 0]})).unwrap();
-        assert!(close(v3(&s, "transform/position"), [300.0 - d / 2.0, 180.0, -800.0]), "{:?}", v3(&s, "transform/position"));
-        // Controls: Center & Left puts the left eye a full separation left; convergence toes in.
-        s.execute("prop.set", json!({"layer": ctl, "path": "effects/#1/configuration", "value": 2})).unwrap();
-        s.execute("prop.set", json!({"layer": ctl, "path": "effects/#1/convergence", "value": true})).unwrap();
-        assert!(close(v3(&s, "transform/position"), [300.0 - d, 180.0, -800.0]), "{:?}", v3(&s, "transform/position"));
-        assert!(close(v3(&s, "transform/poi"), [300.0, 180.0, 0.0]), "{:?}", v3(&s, "transform/poi"));
-    }
-}
+mod tests;
diff --git a/crates/host/src/tests.rs b/crates/host/src/tests.rs
new file mode 100644
index 000000000..020d5f3a1
--- /dev/null
+++ b/crates/host/src/tests.rs
@@ -0,0 +1,547 @@
+use serde_json::json;
+
+#[test]
+fn host_runs_tasks_scheduled_by_panel_handlers() {
+    let mut s = super::session();
+    let result = s.execute("script.run", json!({"code": "var w=new Window('palette','Timer regression'); var b=w.add('button',undefined,'Import'); b.onClick=function(){app.scheduleTask(\"app.project.items.addComp('Scheduled',64,64,1,1,25)\",0,false);};w.show();"})).unwrap();
+    assert_eq!(result["ok"], true, "{result}");
+    s.execute("scriptui.click", json!({"window":"Timer regression","widget":"Import"})).unwrap();
+    assert!(s.project.items.is_empty());
+    let tick = s.execute("script.runTasks", json!({})).unwrap();
+    assert_eq!(tick["ran"], 1, "{tick}");
+    assert_eq!(tick["errors"], json!([]), "{tick}");
+    assert!(s.project.items.values().any(|item| item.name == "Scheduled"));
+    s.execute("scriptui.close", json!({"window":"Timer regression"})).unwrap();
+}
+
+/// Layer ▸ Camera ▸ Link Focus Distance to Point of Interest / to Layer: the expressions
+/// evaluate to the camera's focus on the target.
+#[test]
+fn focus_link_expressions_track_the_target() {
+    use effectcraft_engine::geom::vec3;
+    let mut s = super::session();
+    s.execute("comp.new", json!({"name": "F", "width": 400, "height": 300, "duration": 2})).unwrap();
+    let t = s.execute("layer.newSolid", json!({"color": "#ffffff", "width": 50, "height": 50})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("layer.setSwitch", json!({"layers": [t], "switch": "threeD", "value": true})).unwrap();
+    s.execute("layer.setTransform", json!({"layer": t, "prop": "position", "value": [260, 120, 400]})).unwrap();
+    let cam = s.execute("layer.newCamera", json!({})).unwrap()["layer"].as_u64().unwrap();
+    let cid = s.active_comp_id().unwrap();
+    let focus = |s: &effectcraft_engine::Session| {
+        let comp = s.project.comp(cid).unwrap();
+        let mut ctx = effectcraft_engine::render::EvalCtx::new(&s.project, cid, comp, s.time());
+        ctx.expr = s.expr.as_deref();
+        let l = comp.layer(effectcraft_engine::project::LayerId(cam)).unwrap();
+        ctx.value(l, l.props.prop("cameraOptions/focusDistance").unwrap()).as_f64()
+    };
+    let depth = |s: &effectcraft_engine::Session| {
+        let comp = s.project.comp(cid).unwrap();
+        let ctx = effectcraft_engine::render::EvalCtx::new(&s.project, cid, comp, s.time());
+        let c = comp.layer(effectcraft_engine::project::LayerId(cam)).unwrap();
+        let tl = comp.layer(effectcraft_engine::project::LayerId(t)).unwrap();
+        let cs = effectcraft_engine::render::three_d::camera::layer_camera(&ctx, c);
+        cs.depth(ctx.world_matrix(tl).apply(vec3(25.0, 25.0, 0.0)))
+    };
+    s.execute("layer.select", json!({"layers": [cam, t]})).unwrap();
+    let set = s.execute("camera.setFocusToLayer", json!({})).unwrap()["focusDistance"].as_f64().unwrap();
+    assert!((set - depth(&s)).abs() < 1e-6 && (focus(&s) - set).abs() < 1e-6);
+    s.execute("camera.linkFocusToLayer", json!({})).unwrap();
+    // Move the target: the linked focus follows.
+    s.execute("layer.setTransform", json!({"layer": t, "prop": "position", "value": [200, 150, 900]})).unwrap();
+    assert!((focus(&s) - depth(&s)).abs() < 1e-3, "{} vs {}", focus(&s), depth(&s));
+    s.execute("camera.linkFocusToPoi", json!({"camera": cam})).unwrap();
+    let poi = {
+        let l = s.active_comp().unwrap().layer(effectcraft_engine::project::LayerId(cam)).unwrap();
+        let p = l.props.prop("transform/position").unwrap().value.as_vec3();
+        let q = l.props.prop("transform/poi").unwrap().value.as_vec3();
+        ((p[0] - q[0]).powi(2) + (p[1] - q[1]).powi(2) + (p[2] - q[2]).powi(2)).sqrt()
+    };
+    assert!((focus(&s) - poi).abs() < 1e-6, "{} vs {poi}", focus(&s));
+}
+
+#[test]
+fn wired_session_renders_demo_with_expressions() {
+    let mut s = super::session();
+    s.execute("file.openDemoProject", json!({})).unwrap();
+    let cid = s.active_comp_id().unwrap();
+    let lid = s.active_comp().unwrap().layers[1].id.0;
+    s.execute("prop.setExpression", json!({"layer": lid, "path": "transform/rotation", "expression": "time * 90"})).unwrap();
+    let img = s.render(cid, s.time(), effectcraft_engine::render::RenderOpts { scale: 0.25, ..Default::default() });
+    assert!(img.data.iter().any(|p| p[3] > 0.5));
+}
+
+/// File ▸ Import of glTF/GLB/OBJ models through the media layer, placed as model layers and
+/// drawn by the Advanced 3D renderer.
+#[test]
+fn imported_models_render_in_advanced_3d() {
+    let fx = |n: &str| format!("{}/../model/tests/fixtures/{n}", env!("CARGO_MANIFEST_DIR"));
+    let mut s = super::session();
+    s.execute("comp.new", json!({"name": "M", "width": 160, "height": 120, "renderer": "advanced3d"})).unwrap();
+    let r = s.execute("file.import", json!({"paths": [fx("cube.obj"), fx("quad.glb"), fx("quad.gltf")]})).unwrap();
+    assert_eq!(r["errors"], json!([]), "{r}");
+    let items: Vec<u64> = r["items"].as_array().unwrap().iter().map(|v| v.as_u64().unwrap()).collect();
+    assert_eq!(items.len(), 3);
+    let cube = s.execute("layer.addItem", json!({"item": items[0]})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("prop.set", json!({"layer": cube, "path": "transform/rotationY", "value": 30})).unwrap();
+    s.execute("prop.set", json!({"layer": cube, "path": "transform/rotationX", "value": 20})).unwrap();
+    let cid = s.active_comp_id().unwrap();
+    let opts = effectcraft_engine::render::RenderOpts::default();
+    let img = s.render(cid, s.time(), opts);
+    let covered = img.data.iter().filter(|p| p[3] > 0.99).count();
+    assert!(covered > 1000, "the cube covers part of the frame: {covered}");
+    // Red faces (material Red) are visible.
+    assert!(img.data.iter().any(|p| p[3] > 0.99 && p[0] > 0.5 && p[1] < 0.2));
+    // The textured binary glTF quad.
+    for _ in 0..3 {
+        s.execute("edit.undo", json!({})).unwrap();
+    }
+    s.execute("layer.addItem", json!({"item": items[1]})).unwrap();
+    let img = s.render(cid, s.time(), opts);
+    assert!(img.data.iter().filter(|p| p[3] > 0.99).count() > 1000);
+    // Classic 3D doesn't draw models.
+    s.execute("comp.renderer", json!({"renderer": "classic3d"})).unwrap();
+    assert!(s.render(cid, s.time(), opts).data.iter().all(|p| p[3] == 0.0));
+}
+
+/// A binary glTF of a red cube 2 units wide (positions and indices only).
+fn glb_cube() -> Vec<u8> {
+    let mut bin: Vec<u8> = (0..8u32).flat_map(|i| [i & 1, (i >> 1) & 1, (i >> 2) & 1].map(|b| b as f32 * 2.0 - 1.0)).flat_map(f32::to_le_bytes).collect();
+    let faces: [[u16; 4]; 6] = [[0, 2, 3, 1], [4, 5, 7, 6], [0, 1, 5, 4], [2, 6, 7, 3], [0, 4, 6, 2], [1, 3, 7, 5]];
+    bin.extend(faces.iter().flat_map(|f| [f[0], f[1], f[2], f[0], f[2], f[3]]).flat_map(u16::to_le_bytes));
+    let gltf = json!({
+        "asset": {"version": "2.0"},
+        "scene": 0,
+        "scenes": [{"nodes": [0]}],
+        "nodes": [{"mesh": 0}],
+        "meshes": [{"primitives": [{"attributes": {"POSITION": 0}, "indices": 1, "material": 0}]}],
+        "materials": [{"pbrMetallicRoughness": {"baseColorFactor": [1, 0, 0, 1], "metallicFactor": 0, "roughnessFactor": 1}}],
+        "buffers": [{"byteLength": bin.len()}],
+        "bufferViews": [{"buffer": 0, "byteOffset": 0, "byteLength": 96}, {"buffer": 0, "byteOffset": 96, "byteLength": 72}],
+        "accessors": [
+            {"bufferView": 0, "componentType": 5126, "count": 8, "type": "VEC3", "min": [-1, -1, -1], "max": [1, 1, 1]},
+            {"bufferView": 1, "componentType": 5123, "count": 36, "type": "SCALAR"}
+        ]
+    });
+    let mut text = gltf.to_string().into_bytes();
+    text.resize(text.len().div_ceil(4) * 4, b' ');
+    let chunk = |kind: &[u8; 4], data: &[u8]| [&(data.len() as u32).to_le_bytes()[..], kind, data].concat();
+    let body = [chunk(b"JSON", &text), chunk(b"BIN\0", &bin)].concat();
+    [&b"glTF"[..], &2u32.to_le_bytes(), &(12 + body.len() as u32).to_le_bytes(), &body].concat()
+}
+
+/// #264: a model imported into a new composition (Classic 3D by default) was invisible on
+/// every renderer, because only Advanced 3D draws models. Adding it now switches the comp,
+/// and the software renderer (no GPU, as on the reporter's Intel HD Graphics 5500) draws it.
+#[test]
+fn imported_glb_shows_in_a_new_composition() {
+    let path = std::env::temp_dir().join(format!("effectcraft-264-cube-{}.glb", std::process::id()));
+    std::fs::write(&path, glb_cube()).unwrap();
+    let mut s = super::session();
+    assert!(s.accel.is_none(), "renders in software");
+    let r = s.execute("file.import", json!({"paths": [path.to_string_lossy()]})).unwrap();
+    assert_eq!(r["errors"], json!([]), "{r}");
+    s.state.project_selection = vec![effectcraft_project::ItemId(r["items"][0].as_u64().unwrap())];
+    s.execute("file.newCompFromSelection", json!({})).unwrap();
+    let comp = s.active_comp().unwrap();
+    assert_eq!(comp.renderer, effectcraft_project::Renderer::Advanced3D);
+    let layer = comp.layers[0].id.0;
+    s.execute("prop.set", json!({"layer": layer, "path": "transform/rotationY", "value": 30})).unwrap();
+    s.execute("prop.set", json!({"layer": layer, "path": "transform/rotationX", "value": 20})).unwrap();
+    let cid = s.active_comp_id().unwrap();
+    let img = s.render(cid, s.time(), effectcraft_engine::render::RenderOpts { scale: 0.25, ..Default::default() });
+    let red = img.data.iter().filter(|p| p[3] > 0.99 && p[0] > 0.2 && p[1] < 0.05 && p[2] < 0.05).count();
+    let _ = std::fs::remove_file(&path);
+    // Half the comp height wide, seen at an angle: well over 5% of the frame.
+    assert!(red * 20 > img.data.len(), "red cube pixels: {red} of {}", img.data.len());
+}
+
+/// #651: an animated GIF imported from disk plays: the layer shows each frame at its time,
+/// in the viewer's renders and in exports alike.
+#[test]
+fn an_imported_animated_gif_plays() {
+    let dir = std::env::temp_dir().join(format!("ec-gif-{}", std::process::id()));
+    std::fs::create_dir_all(&dir).unwrap();
+    let path = dir.join("anim.gif");
+    let mut bytes = Vec::new();
+    {
+        let mut enc = gif::Encoder::new(&mut bytes, 4, 4, &[]).unwrap();
+        for rgb in [[255u8, 0, 0], [0, 255, 0], [0, 0, 255]] {
+            let mut f = gif::Frame::from_rgb(4, 4, &rgb.repeat(16));
+            f.delay = 10;
+            enc.write_frame(&f).unwrap();
+        }
+    }
+    std::fs::write(&path, bytes).unwrap();
+    let mut s = super::session();
+    s.execute("comp.new", json!({"name": "G", "width": 4, "height": 4, "frameRate": 30, "duration": 1})).unwrap();
+    s.execute("file.import", json!({"paths": [path.to_string_lossy()], "addToComp": true})).unwrap();
+    let cid = s.active_comp_id().unwrap();
+    let rgb = |t: f64| {
+        let img = s.render(cid, effectcraft_time::Tick::from_seconds_f64(t), effectcraft_engine::render::RenderOpts::default());
+        let p = img.data[5];
+        [p[0].round(), p[1].round(), p[2].round()]
+    };
+    assert_eq!(rgb(0.05), [1.0, 0.0, 0.0]);
+    assert_eq!(rgb(0.15), [0.0, 1.0, 0.0]);
+    assert_eq!(rgb(0.25), [0.0, 0.0, 1.0]);
+    let _ = std::fs::remove_dir_all(dir);
+}
+
+/// The web app's path: outputs go to a sink (downloads), never to the file system.
+#[test]
+fn render_queue_exports_to_a_sink() {
+    use std::sync::{Arc, Mutex};
+    let got: Arc<Mutex<Vec<(String, Vec<u8>)>>> = Arc::default();
+    let g = got.clone();
+    let mut s = super::session();
+    s.exporter = Some(Arc::new(super::FileExporter { sink: Some(Arc::new(move |p: &str, d: Vec<u8>| g.lock().unwrap().push((p.to_string(), d)))) }));
+    s.execute("file.openDemoProject", json!({})).unwrap();
+    // Rooted without a drive letter is not absolute on Windows, where the engine joins it to the home drive.
+    let dir = if cfg!(windows) { "C:/no-such-dir-effectcraft-sink-test" } else { "/no-such-dir-effectcraft-sink-test" };
+    s.execute(
+        "renderQueue.add",
+        json!({"format": "gif", "output": format!("{dir}/a.gif"), "resolution": 0.0625, "timeSpan": "custom", "start": 0.0, "end": 0.2}),
+    )
+    .unwrap();
+    s.execute(
+        "renderQueue.add",
+        json!({"format": "png", "output": format!("{dir}/seq_[##].png"), "resolution": 0.0625, "timeSpan": "custom", "start": 0.0, "end": 0.1}),
+    )
+    .unwrap();
+    s.execute("renderQueue.render", json!({"wait": true})).unwrap();
+    s.poll_render();
+    let mut got = got.lock().unwrap().clone();
+    got.sort_by(|a, b| a.0.cmp(&b.0));
+    let names: Vec<std::path::PathBuf> = got.iter().map(|(p, _)| std::path::PathBuf::from(p)).collect();
+    let expected = [format!("{dir}/a.gif"), format!("{dir}/seq_00.png"), format!("{dir}/seq_01.png"), format!("{dir}/seq_02.png")]
+        .map(|p| std::path::absolute(p).unwrap());
+    assert_eq!(names, expected);
+    assert!(got[0].1.starts_with(b"GIF89a"));
+    assert!(got[1].1.starts_with(b"\x89PNG"));
+    assert!(!std::path::Path::new(dir).exists());
+}
+
+#[test]
+fn render_queue_exports_demo_comp() {
+    let dir = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../../target/test-out/host-rq");
+    let _ = std::fs::remove_dir_all(&dir);
+    let mut s = super::session();
+    s.execute("file.openDemoProject", json!({})).unwrap();
+    let out = dir.join("[compName]_[width]x[height].[fileExtension]");
+    let r = s
+        .execute(
+            "renderQueue.add",
+            json!({"format": "h264", "output": out.to_string_lossy(), "resolution": 0.125, "timeSpan": "custom", "start": 0.0, "end": 0.4}),
+        )
+        .unwrap();
+    let path = r["outputPath"].as_str().unwrap().to_string();
+    assert!(path.ends_with("_240x134.mp4"), "{path}");
+    // A second item: PNG sequence, rendered in the background.
+    s.execute("renderQueue.add", json!({"format": "png", "output": dir.join("seq_[###].png").to_string_lossy(), "resolution": 0.0625, "timeSpan": "custom", "start": 0.0, "end": 0.2})).unwrap();
+    let r = s.execute("renderQueue.render", json!({"wait": false})).unwrap();
+    assert_eq!(r["items"].as_array().unwrap().len(), 2);
+    let t0 = std::time::Instant::now();
+    while s.is_rendering() {
+        assert!(t0.elapsed().as_secs() < 300, "render timed out");
+        std::thread::sleep(std::time::Duration::from_millis(20));
+        s.poll_render();
+    }
+    s.poll_render();
+    let list = s.execute("renderQueue.list", json!({})).unwrap();
+    for it in list["items"].as_array().unwrap() {
+        assert_eq!(it["statusLabel"], "Done", "{it}");
+        assert!(it["render_time"].as_f64().is_some());
+        assert!(std::path::Path::new(it["last_output"].as_str().unwrap()).exists(), "{it}");
+    }
+    assert!(std::path::Path::new(&path).metadata().unwrap().len() > 500);
+    assert!(dir.join("seq_000.png").exists() && dir.join("seq_005.png").exists() && !dir.join("seq_006.png").exists());
+    // Rendering again needs a re-queue.
+    assert!(s.execute("renderQueue.render", json!({})).is_err());
+    s.execute("renderQueue.setRender", json!({"index": 1, "render": true})).unwrap();
+    assert_eq!(s.project.render_queue[0].status, effectcraft_engine::project::render_queue::RenderStatus::Queued);
+}
+
+/// Value of a property of layer `l` at time 0 (keys + expression).
+fn value(s: &effectcraft_engine::Session, l: u64, path: &str) -> effectcraft_engine::keyframe::Value {
+    let cid = s.active_comp_id().unwrap();
+    let comp = s.project.comp(cid).unwrap();
+    let layer = comp.layer(effectcraft_engine::project::LayerId(l)).unwrap();
+    let ctx =
+        effectcraft_engine::render::EvalCtx { project: &s.project, comp_id: cid, comp, time: Default::default(), expr: s.expr.as_deref(), footage: None };
+    ctx.value(layer, layer.props.prop(path).unwrap())
+}
+
+#[test]
+fn pick_whip_expressions_evaluate() {
+    let mut s = super::session();
+    s.execute("comp.new", json!({"name": "C", "width": 200, "height": 200, "frameRate": 30, "duration": 2})).unwrap();
+    let a = s.execute("layer.newSolid", json!({"color": "#ffffff"})).unwrap()["layer"].as_u64().unwrap();
+    let b = s.execute("layer.newSolid", json!({"name": "Src", "color": "#ff0000"})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("prop.set", json!({"layer": b, "path": "transform/rotation", "value": 33})).unwrap();
+    s.execute("prop.set", json!({"layer": b, "path": "transform/position", "value": [12, 34]})).unwrap();
+    s.execute("effect.apply", json!({"layer": b, "effect": "Gaussian Blur"})).unwrap();
+    s.execute("prop.set", json!({"layer": b, "path": "effects/#1/blurriness", "value": 21})).unwrap();
+    s.execute("layer.addMask", json!({"layer": b})).unwrap();
+    s.execute("prop.set", json!({"layer": b, "path": "masks/#1/feather", "value": [7, 7]})).unwrap();
+    let link = |s: &mut effectcraft_engine::Session, from: &str, to: &str| {
+        s.execute("prop.pickWhip", json!({"layer": a, "path": from, "target": {"layer": b, "path": to}})).unwrap();
+    };
+    link(&mut s, "transform/opacity", "transform/rotation");
+    assert_eq!(value(&s, a, "transform/opacity").as_f64(), 33.0);
+    link(&mut s, "transform/scale", "transform/rotation");
+    let cid = s.active_comp_id().unwrap();
+    let ep = effectcraft_expr::eval_property(&s.project, cid, effectcraft_engine::project::LayerId(a), "transform/scale", 0.0);
+    assert!(ep.is_ok(), "{ep:?}");
+    assert_eq!(value(&s, a, "transform/scale").as_vec2(), [33.0, 33.0]);
+    link(&mut s, "transform/position", "transform/position");
+    assert_eq!(value(&s, a, "transform/position").as_vec2(), [12.0, 34.0]);
+    link(&mut s, "transform/rotation", "effects/#1/blurriness");
+    assert_eq!(value(&s, a, "transform/rotation").as_f64(), 21.0);
+    link(&mut s, "transform/opacity", "masks/#1/feather");
+    assert_eq!(value(&s, a, "transform/opacity").as_f64(), 7.0);
+    // Separated dimensions: X Position reference.
+    s.execute("prop.separateDimensions", json!({"layer": b})).unwrap();
+    link(&mut s, "transform/rotation", "transform/positionX");
+    assert_eq!(value(&s, a, "transform/rotation").as_f64(), 12.0);
+}
+
+/// The expression error bar's list: evaluation errors and syntax errors, with the layer and
+/// property they belong to.
+#[test]
+fn expression_errors_are_collected() {
+    let mut s = super::session();
+    s.execute("comp.new", json!({"name": "C", "width": 100, "height": 100, "frameRate": 30, "duration": 2})).unwrap();
+    let a = s.execute("layer.newSolid", json!({"name": "Box", "color": "#ffffff"})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("prop.setExpression", json!({"layer": a, "path": "transform/opacity", "expression": "50"})).unwrap();
+    assert_eq!(s.execute("expr.errors", json!({})).unwrap()["count"], 0);
+    s.execute("prop.setExpression", json!({"layer": a, "path": "transform/rotation", "expression": "thisComp.layer(\"Nope\").rotation"})).unwrap();
+    s.execute("prop.setExpression", json!({"layer": a, "path": "transform/opacity", "expression": "1 +* ("})).unwrap();
+    let r = s.execute("expr.errors", json!({})).unwrap();
+    assert_eq!(r["count"], 2, "{r}");
+    let errs = r["errors"].as_array().unwrap();
+    let rot = errs.iter().find(|e| e["path"] == "transform/rotation").unwrap();
+    assert!(rot["message"].as_str().unwrap().contains("Nope"), "{rot}");
+    assert_eq!(rot["layerIndex"], 1);
+    assert_eq!(rot["layerName"], "Box");
+    assert_eq!(rot["disabled"], false);
+    let op = errs.iter().find(|e| e["path"] == "transform/opacity").unwrap();
+    assert_eq!(op["disabled"], true);
+    assert!(r["text"][0].as_str().unwrap().contains("of layer 1 ('Box') in comp 'C'"), "{r}");
+    // A user-disabled (but valid) expression is not an error.
+    s.execute("prop.setExpression", json!({"layer": a, "path": "transform/rotation", "expression": "45"})).unwrap();
+    s.execute("prop.setExpression", json!({"layer": a, "path": "transform/rotation", "enabled": false})).unwrap();
+    assert_eq!(s.execute("expr.errors", json!({})).unwrap()["count"], 1);
+    // The Expression Language menu is categorised.
+    let m = s.execute("expr.languageMenu", json!({})).unwrap();
+    assert!(m.as_array().unwrap().iter().any(|c| c["category"] == "Footage" && c["items"].as_array().unwrap().iter().any(|i| i["text"] == "sourceData")));
+}
+
+/// File ▸ Import of JSON/CSV data files as data footage, read by expressions.
+#[test]
+fn imported_data_files_drive_expressions() {
+    let dir = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../../target/test-out/host-data");
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).unwrap();
+    std::fs::write(dir.join("levels.csv"), "label,value\nlow,10\nhigh,90\n").unwrap();
+    std::fs::write(dir.join("cfg.json"), r#"{"angle": 33}"#).unwrap();
+    std::fs::write(dir.join("broken.json"), "{nope").unwrap();
+    let mut s = super::session();
+    s.execute("comp.new", json!({"name": "C", "width": 100, "height": 100, "frameRate": 30, "duration": 2})).unwrap();
+    let paths: Vec<String> = ["levels.csv", "cfg.json", "broken.json"].iter().map(|n| dir.join(n).to_string_lossy().to_string()).collect();
+    let r = s.execute("file.import", json!({"paths": paths})).unwrap();
+    assert_eq!(r["items"].as_array().unwrap().len(), 2, "{r}");
+    assert_eq!(r["errors"].as_array().unwrap().len(), 1, "{r}");
+    let csv = r["items"][0].as_u64().unwrap();
+    assert_eq!(s.project.item(effectcraft_engine::project::ItemId(csv)).unwrap().type_name(), "Data");
+    assert!(s.execute("layer.addItem", json!({"item": csv})).is_err(), "data files are not layers");
+    let a = s.execute("layer.newSolid", json!({"color": "#ffffff"})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("prop.setExpression", json!({"layer": a, "path": "transform/opacity", "expression": "footage(\"levels.csv\").sourceData[1].value"})).unwrap();
+    s.execute("prop.setExpression", json!({"layer": a, "path": "transform/rotation", "expression": "footage(\"cfg.json\").sourceData.angle"})).unwrap();
+    assert_eq!(value(&s, a, "transform/opacity").as_f64(), 90.0);
+    assert_eq!(value(&s, a, "transform/rotation").as_f64(), 33.0);
+}
+
+/// sampleImage through the renderer: a box's Fill colour follows the solid under it.
+#[test]
+fn sample_image_drives_a_colour() {
+    let mut s = super::session();
+    s.execute("comp.new", json!({"name": "C", "width": 100, "height": 100, "frameRate": 30, "duration": 2})).unwrap();
+    s.execute("layer.newSolid", json!({"name": "Bg", "color": "#00ff00"})).unwrap();
+    let a = s.execute("layer.newSolid", json!({"name": "Fg", "color": "#ffffff", "width": 20, "height": 20})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("effect.apply", json!({"layer": a, "effect": "Fill"})).unwrap();
+    s.execute(
+        "prop.setExpression",
+        json!({"layer": a, "path": "effects/#1/color", "expression": "thisComp.layer(\"Bg\").sampleImage(thisComp.layer(\"Bg\").fromComp(toComp(anchorPoint)))"}),
+    )
+    .unwrap();
+    let cid = s.active_comp_id().unwrap();
+    let img = s.render(cid, s.time(), effectcraft_engine::render::RenderOpts::default());
+    let px = img.get(50, 50);
+    assert!(px[1] > 0.99 && px[0] < 0.01, "the box is filled with the sampled green: {px:?}");
+}
+
+/// Proxies through the real media and export layers: Render Settings ▸ Proxy Use decides
+/// whether an export uses the proxy, and Create Proxy renders and attaches one.
+#[test]
+fn proxies_in_exports_and_create_proxy() {
+    let dir = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../../target/test-out/host-proxy");
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).unwrap();
+    let p = |n: &str| dir.join(n).to_string_lossy().to_string();
+    let mut s = super::session();
+    // Source and proxy stills, written by the app itself.
+    s.execute("comp.new", json!({"name": "Red", "width": 16, "height": 16, "frameRate": 10, "duration": 1})).unwrap();
+    let red = s.active_comp_id().unwrap();
+    s.execute("layer.newSolid", json!({"color": "#ff0000"})).unwrap();
+    s.execute("comp.saveFrameAs", json!({"path": p("red.png")})).unwrap();
+    s.execute("comp.new", json!({"name": "Blue", "width": 8, "height": 8, "frameRate": 10, "duration": 1})).unwrap();
+    s.execute("layer.newSolid", json!({"color": "#0000ff"})).unwrap();
+    s.execute("comp.saveFrameAs", json!({"path": p("blue.png")})).unwrap();
+    let foot = s.execute("file.import", json!({"paths": [p("red.png")]})).unwrap()["items"][0].as_u64().unwrap();
+    s.execute("file.setProxy", json!({"item": foot, "path": p("blue.png")})).unwrap();
+    s.execute("comp.new", json!({"name": "Out", "width": 16, "height": 16, "frameRate": 10, "duration": 1})).unwrap();
+    let out = s.active_comp_id().unwrap();
+    s.execute("layer.addItem", json!({"item": foot})).unwrap();
+    // Export one frame with each Proxy Use.
+    for (name, using) in [("all", "use_all_[#].png"), ("none", "use_none_[#].png")] {
+        s.execute(
+            "renderQueue.add",
+            json!({"comp": out.0, "format": "png", "output": p(using), "timeSpan": "custom", "start": 0.0, "end": 0.1, "proxyUse": name}),
+        )
+        .unwrap();
+    }
+    s.execute("renderQueue.render", json!({"wait": true})).unwrap();
+    s.poll_render();
+    let centre = |s: &mut effectcraft_engine::Session, path: &str| {
+        let id = s.execute("file.import", json!({"paths": [path]})).unwrap()["items"][0].as_u64().unwrap();
+        s.execute("comp.new", json!({"name": "Probe", "width": 16, "height": 16, "frameRate": 10, "duration": 1})).unwrap();
+        s.execute("layer.addItem", json!({"item": id})).unwrap();
+        let c = s.active_comp_id().unwrap();
+        s.render(c, Default::default(), Default::default()).get(8, 8)
+    };
+    let all = centre(&mut s, &p("use_all_0.png"));
+    assert!(all[2] > 0.99 && all[0] < 0.01, "Use All Proxies renders the blue proxy: {all:?}");
+    let none = centre(&mut s, &p("use_none_0.png"));
+    assert!(none[0] > 0.99 && none[2] < 0.01, "Use No Proxies renders the red source: {none:?}");
+    // Create Proxy ▸ Still: rendered at half size and attached to the comp.
+    s.execute("file.createProxy", json!({"kind": "still", "comp": red.0, "path": p("red_proxy_[#####].png")})).unwrap();
+    s.execute("renderQueue.render", json!({"wait": true})).unwrap();
+    s.poll_render();
+    let px = s.project.item(red).unwrap().proxy.clone().expect("Create Proxy attached the rendered still");
+    assert!(px.enabled);
+    assert_eq!((px.footage.width, px.footage.height), (8, 8));
+    assert!(std::path::Path::new(&px.footage.path).exists(), "{}", px.footage.path);
+}
+
+/// A script builds a comp, queues it and renders it through the Render Queue.
+#[test]
+fn script_renders_through_the_render_queue() {
+    let dir = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../../target/test-out/host-script");
+    let _ = std::fs::remove_dir_all(&dir);
+    let out = dir.join("scripted.gif");
+    let mut s = super::session();
+    let code = format!(
+        r#"
+            var comp = app.project.items.addComp("Scripted", 64, 48, 1, 0.2, 10);
+            var sq = comp.layers.addSolid([1, 0.5, 0], "Square", 16, 16, 1);
+            sq.transform.position.setValueAtTime(0, [8, 24]);
+            sq.transform.position.setValueAtTime(0.1, [56, 24]);
+            var item = app.project.renderQueue.items.add(comp);
+            item.outputModule(1).applyTemplate("GIF");
+            item.outputModule(1).file = new File({});
+            app.project.renderQueue.render();
+            [item.status == RQItemStatus.DONE, item.outputModule(1).file.fsName, app.project.renderQueue.numItems]
+            "#,
+        serde_json::to_string(&out.to_string_lossy()).unwrap()
+    );
+    let r = s.execute("script.run", json!({"code": code})).unwrap();
+    assert_eq!(r["ok"], json!(true), "{r}");
+    assert_eq!(r["result"][0], json!(true), "{r}");
+    assert_eq!(r["result"][2], json!(1));
+    let bytes = std::fs::read(&out).unwrap();
+    assert!(bytes.starts_with(b"GIF89a"));
+}
+
+/// importFile, layers.add(footage) and project save/open from a script.
+#[test]
+fn script_imports_footage_and_saves() {
+    let dir = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../../target/test-out/host-script-import");
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).unwrap();
+    let q = |n: &str| serde_json::to_string(&dir.join(n).to_string_lossy()).unwrap();
+    let mut s = super::session();
+    let code = format!(
+        r#"
+            var c = app.project.items.addComp("Src", 32, 32, 1, 1, 10);
+            c.layers.addSolid([0, 1, 0], "G", 32, 32, 1);
+            app.run("comp.saveFrameAs", {{comp: c.id, path: {png}}});
+            var still = app.project.importFile(new ImportOptions(new File({png})));
+            var main = app.project.items.addComp("Main", 64, 64, 1, 1, 10);
+            var l = main.layers.add(still);
+            app.project.save(new File({proj}));
+            [still instanceof FootageItem, still.width, still.mainSource.isStill, l.source.name, app.project.file.name]
+            "#,
+        png = q("frame.png"),
+        proj = q("p.ecproj")
+    );
+    let r = s.execute("script.run", json!({"code": code})).unwrap();
+    assert_eq!(r["ok"], json!(true), "{r}");
+    assert_eq!(r["result"], json!([true, 32, true, "frame.png", "p.ecproj"]), "{r}");
+    let r = s.execute("script.run", json!({"code": format!("app.open(new File({})); app.project.numItems", q("p.ecproj"))})).unwrap();
+    assert_eq!(r["result"], json!(5), "{r}"); // Src, Solids, G, frame.png, Main
+}
+
+#[test]
+fn expression_syntax_errors_disable_the_expression() {
+    let mut s = super::session();
+    s.execute("comp.new", json!({"name": "C", "width": 100, "height": 100, "frameRate": 30, "duration": 2})).unwrap();
+    let a = s.execute("layer.newSolid", json!({"color": "#ffffff"})).unwrap()["layer"].as_u64().unwrap();
+    let r = s.execute("prop.setExpression", json!({"layer": a, "path": "transform/opacity", "expression": "1 +* ("})).unwrap();
+    assert!(r["error"].is_string(), "{r}");
+    let pr = s.active_comp().unwrap().layers[0].props.prop("transform/opacity").unwrap().clone();
+    assert!(!pr.expr.unwrap().enabled);
+    assert_eq!(value(&s, a, "transform/opacity").as_f64(), 100.0);
+    s.execute("prop.setExpression", json!({"layer": a, "path": "transform/opacity", "expression": "50"})).unwrap();
+    assert_eq!(value(&s, a, "transform/opacity").as_f64(), 50.0);
+}
+/// Create Stereo 3D Rig: the eye cameras' expressions follow the master camera and the
+/// Stereo 3D Controls (and agree with the values the command wrote).
+#[test]
+fn stereo_rig_expressions_follow_the_master_camera() {
+    let mut s = super::session();
+    s.execute("comp.new", json!({"name": "Shot", "width": 640, "height": 360, "frameRate": 30, "duration": 2})).unwrap();
+    let src = s.active_comp_id().unwrap();
+    let cam = s.execute("layer.newCamera", json!({"name": "Main", "position": [320, 180, -800], "poi": [320, 180, 0], "zoom": 900})).unwrap()["layer"]
+        .as_u64()
+        .unwrap();
+    let r = s.execute("camera.stereoRig", json!({"sceneDepth": 4})).unwrap();
+    let ctl = r["controls"].as_u64().unwrap();
+    let left = effectcraft_engine::project::ItemId(r["leftComp"].as_u64().unwrap());
+    // The left eye camera's evaluated value (expressions on).
+    let v3 = |s: &effectcraft_engine::Session, path: &str| {
+        let comp = s.project.comp(left).unwrap();
+        let layer = &comp.layers[0];
+        let ctx = effectcraft_engine::render::EvalCtx {
+            project: &s.project,
+            comp_id: left,
+            comp,
+            time: Default::default(),
+            expr: s.expr.as_deref(),
+            footage: None,
+        };
+        ctx.value(layer, layer.props.prop(path).unwrap()).as_vec3()
+    };
+    let close = |a: [f64; 3], b: [f64; 3]| (0..3).all(|i| (a[i] - b[i]).abs() < 1e-6);
+    let d = 0.04 * 640.0;
+    assert!(close(v3(&s, "transform/position"), [320.0 - d / 2.0, 180.0, -800.0]), "{:?}", v3(&s, "transform/position"));
+    assert!(close(v3(&s, "transform/poi"), [320.0 - d / 2.0, 180.0, 0.0]), "{:?}", v3(&s, "transform/poi"));
+    // Moving the master moves the eyes.
+    s.execute("comp.open", json!({"comp": src.0})).unwrap();
+    s.execute("prop.set", json!({"layer": cam, "path": "transform/position", "value": [300, 180, -800]})).unwrap();
+    s.execute("prop.set", json!({"layer": cam, "path": "transform/poi", "value": [300, 180, 0]})).unwrap();
+    assert!(close(v3(&s, "transform/position"), [300.0 - d / 2.0, 180.0, -800.0]), "{:?}", v3(&s, "transform/position"));
+    // Controls: Center & Left puts the left eye a full separation left; convergence toes in.
+    s.execute("prop.set", json!({"layer": ctl, "path": "effects/#1/configuration", "value": 2})).unwrap();
+    s.execute("prop.set", json!({"layer": ctl, "path": "effects/#1/convergence", "value": true})).unwrap();
+    assert!(close(v3(&s, "transform/position"), [300.0 - d, 180.0, -800.0]), "{:?}", v3(&s, "transform/position"));
+    assert!(close(v3(&s, "transform/poi"), [300.0, 180.0, 0.0]), "{:?}", v3(&s, "transform/poi"));
+}