diff --git a/crates/engine/tests/command_sweep.rs b/crates/engine/tests/command_sweep.rs
index 4bfd1152d..fcf1138b9 100644
--- a/crates/engine/tests/command_sweep.rs
+++ b/crates/engine/tests/command_sweep.rs
@@ -17,10 +17,19 @@ fn safe_path() -> String {
     vectorcraft_testkit::temp_dir("sweep").join("out.bin").to_string_lossy().to_string()
 }
 
+/// `r`, after failing the case if the command panicked. The engine's guard reports a panic as
+/// `EngineError::Internal`.
+fn no_panic(r: Result<Value, vectorcraft_engine::EngineError>) -> Result<Value, vectorcraft_engine::EngineError> {
+    if let Err(vectorcraft_engine::EngineError::Internal { cmd, msg }) = &r {
+        panic!("{cmd} panicked: {msg}");
+    }
+    r
+}
+
 /// Run one call; returns a failure description or None.
 fn probe(fx: Fixture, id: &str, params: &Value) -> Option<String> {
     let mut s = fx.session();
-    let r = catch_quiet(|| s.execute(id, params));
+    let r = catch_quiet(|| no_panic(s.execute(id, params)));
     match r {
         Err(msg) => Some(format!("PANIC {id} {params} [{fx:?}]: {msg}")),
         Ok(_) => {
@@ -68,7 +77,7 @@ fn every_command_without_a_document() {
     let mut failures = vec![];
     for c in command_specs() {
         let mut s = Session::new();
-        match catch_quiet(|| s.execute(c.id, &json!({}))) {
+        match catch_quiet(|| no_panic(s.execute(c.id, &json!({})))) {
             Err(p) => failures.push(format!("PANIC {} with no document: {p}", c.id)),
             // Anything that needs a document must say so via enablement, not fail later.
             Ok(Err(vectorcraft_engine::EngineError::NoDocument)) => failures.push(format!("{}: enabled without a document but needs one", c.id)),
@@ -106,7 +115,7 @@ fn bug_huge_transform_makes_document_unloadable() {
         ("object.distributeSpacing", json!({"spacing": 1e308})),
     ] {
         let mut s = Fixture::Multi.session();
-        if s.execute(id, &p).is_ok() {
+        if no_panic(s.execute(id, &p)).is_ok() {
             vectorcraft_testkit::invariants::check_native_roundtrip(&s.doc().unwrap().doc).unwrap_or_else(|e| panic!("{id} {p}: {e}"));
         }
     }
@@ -117,7 +126,7 @@ fn bug_artboard_huge_props_break_svg() {
     for key in ["x", "y", "width", "height"] {
         let mut s = Fixture::Single.session();
         let p = json!({"index": 0, key: 1e308});
-        if s.execute("artboard.setProps", &p).is_ok() {
+        if no_panic(s.execute("artboard.setProps", &p)).is_ok() {
             vectorcraft_testkit::invariants::check_svg_roundtrip(&s.doc().unwrap().doc).unwrap_or_else(|e| panic!("{p}: {}", &e[..e.len().min(200)]));
         }
     }
@@ -412,14 +421,14 @@ fn area_options_fit_junk() {
     for (size, (w, h)) in [(12.0, (120.0, 40.0)), (0.1, (1.0, 1.0)), (1296.0, (100_000.0, 1.0))] {
         for p in &cases {
             let mut s = Fixture::Multi.session();
-            let made = s.execute("text.create", &json!({"x": 10, "y": 10, "size": size, "text": story, "area": {"width": w, "height": h}}));
+            let made = no_panic(s.execute("text.create", &json!({"x": 10, "y": 10, "size": size, "text": story, "area": {"width": w, "height": h}})));
             let Ok(made) = made else { continue };
             let id = made["id"].as_u64().unwrap_or(0);
-            let r = catch_quiet(|| s.execute("text.areaOptions", p));
+            let r = catch_quiet(|| no_panic(s.execute("text.areaOptions", p)));
             match r {
                 Err(m) => failures.push(format!("PANIC text.areaOptions {p} [{size} pt, {w}×{h}]: {m}")),
                 Ok(_) => {
-                    let typed = catch_quiet(|| s.execute("text.editRange", &json!({"id": id, "start": 0, "insert": "More words. "})));
+                    let typed = catch_quiet(|| no_panic(s.execute("text.editRange", &json!({"id": id, "start": 0, "insert": "More words. "}))));
                     if typed.is_err() {
                         failures.push(format!("PANIC typing after text.areaOptions {p}"));
                     }
@@ -447,11 +456,13 @@ fn polygon_properties_junk() {
     for scale in [None, Some((300.0, 20.0)), Some((1e-300, 100.0))] {
         for p in &cases {
             let mut s = Fixture::Multi.session();
-            let Ok(_) = s.execute("shape.polygon", &json!({"cx": 100, "cy": 100, "radius": 40, "sides": 7, "rotation": 10})) else { continue };
+            let Ok(_) = no_panic(s.execute("shape.polygon", &json!({"cx": 100, "cy": 100, "radius": 40, "sides": 7, "rotation": 10}))) else {
+                continue;
+            };
             if let Some((sx, sy)) = scale {
-                let _ = s.execute("object.scale", &json!({"sx": sx, "sy": sy}));
+                let _ = no_panic(s.execute("object.scale", &json!({"sx": sx, "sy": sy})));
             }
-            match catch_quiet(|| s.execute("object.setLiveShape", p)) {
+            match catch_quiet(|| no_panic(s.execute("object.setLiveShape", p))) {
                 Err(m) => failures.push(format!("PANIC object.setLiveShape {p} [{scale:?}]: {m}")),
                 Ok(_) => {
                     if let Err(e) = catch_quiet(|| check_all(&mut s)).unwrap_or_else(|m| Err(format!("panic in checks: {m}"))) {
@@ -504,7 +515,7 @@ fn every_command_undoes_exactly() {
         let depth = s.doc().unwrap().history.undo.len();
         let Ok(Ok(_)) = catch_quiet(|| s.execute(c.id, &json!({}))) else { continue };
         if s.doc().unwrap().history.undo.len() > depth {
-            let _ = s.execute("edit.undo", &json!({}));
+            let _ = no_panic(s.execute("edit.undo", &json!({})));
             let after = doc_json(&s.doc().unwrap().doc);
             if after != before {
                 failures.push(format!("{}: {}", c.id, vectorcraft_testkit::invariants::first_diff(&before, &after, "$")));
@@ -543,7 +554,7 @@ fn recovery_commands_with_a_damaged_store_and_junk_params() {
             for p in std::iter::once(json!({})).chain(junk_params(spec.params, &path)) {
                 let mut s = fx.session();
                 s.recovery.set_store(store.clone());
-                let r = catch_quiet(|| s.execute(id, &p));
+                let r = catch_quiet(|| no_panic(s.execute(id, &p)));
                 assert!(r.is_ok(), "PANIC {id} {p} [{fx:?}]");
                 check_session(&s).unwrap_or_else(|e| panic!("{id} {p} [{fx:?}]: {e}"));
             }
@@ -576,9 +587,9 @@ fn envelope_commands_with_junk_params_on_envelopes() {
                         continue;
                     }
                     if editing {
-                        let _ = s.execute("object.envelope.editContents", &json!({"editing": true}));
+                        let _ = no_panic(s.execute("object.envelope.editContents", &json!({"editing": true})));
                     }
-                    let r = catch_quiet(|| s.execute(id, &p));
+                    let r = catch_quiet(|| no_panic(s.execute(id, &p)));
                     if r.is_err() {
                         failures.push(format!("PANIC {id} {p} [{make}, editing {editing}]"));
                     } else if s.in_interaction() {
@@ -646,7 +657,7 @@ fn text_commands_with_junk_params_on_inline_graphics() {
     let mut failures = vec![];
     let mut run = |id: &str, p: &Value| {
         let (mut s, _) = setup();
-        match catch_quiet(|| s.execute(id, p)) {
+        match catch_quiet(|| no_panic(s.execute(id, p))) {
             Err(msg) => failures.push(format!("PANIC {id} {p}: {msg}")),
             Ok(r) => {
                 if s.in_interaction() {
diff --git a/crates/engine/tests/import_fuzz.rs b/crates/engine/tests/import_fuzz.rs
index ba7f6fe15..7bad66218 100644
--- a/crates/engine/tests/import_fuzz.rs
+++ b/crates/engine/tests/import_fuzz.rs
@@ -260,8 +260,8 @@ proptest! {
             let mut s = vectorcraft_engine::Session::new();
             s.execute("file.new", &json!({"width":100,"height":100})).unwrap();
             let p = json!({"name":"renamed.png", "dataBase64":vectorcraft_format::base64_encode(&bytes)});
-            for cmd in ["file.place", "file.place.info"] { assert!(s.execute(cmd, &p).is_err()); }
-            assert!(s.execute("file.place.queue", &json!({"files":[p]})).is_err());
+            for cmd in ["file.place", "file.place.info"] { assert!(no_panic(s.execute(cmd, &p)).is_err()); }
+            assert!(no_panic(s.execute("file.place.queue", &json!({"files":[p]}))).is_err());
         });
         prop_assert!(r.is_ok(), "Affinity placement panicked: {:?}", r.err());
     }
@@ -669,8 +669,8 @@ proptest! {
         let r = catch_quiet(|| {
             let mut s = vectorcraft_engine::Session::new();
             let p = json!({"name": "x.pdf", "dataBase64": b64, "pages": pages, "cropTo": crop, "password": password, "thumbnail": 1, "thumbnailSize": 64});
-            let _ = s.execute("document.pdfInfo", &p);
-            if s.execute("document.open", &p).is_ok() {
+            let _ = no_panic(s.execute("document.pdfInfo", &p));
+            if no_panic(s.execute("document.open", &p)).is_ok() {
                 let d = (*s.doc().unwrap().doc).clone();
                 survive("pdf options", || Some(d)).unwrap();
             }
@@ -1037,8 +1037,8 @@ proptest! {
             let mut s = vectorcraft_engine::Session::new();
             s.execute("file.new", &json!({"width": 100, "height": 100})).unwrap();
             let p = json!({"name": name, "dataBase64": vectorcraft_format::base64_encode(&bytes), "thumbnail": 8});
-            let _ = s.execute("file.place.info", &p);
-            let _ = s.execute("file.place", &p);
+            let _ = no_panic(s.execute("file.place.info", &p));
+            let _ = no_panic(s.execute("file.place", &p));
         });
         prop_assert!(r.is_ok(), "{name}: panicked: {:?}", r.err());
     }
@@ -1133,10 +1133,10 @@ fn paste_from_elsewhere(cmd: &str, p: Value) -> Result<(), TestCaseError> {
     let r = catch_quiet(|| {
         let mut s = vectorcraft_engine::Session::new();
         s.execute("file.new", &json!({"width": 100, "height": 100})).unwrap();
-        if s.execute(cmd, &p).is_ok() {
+        if no_panic(s.execute(cmd, &p)).is_ok() {
             // Paste may refuse what it was given, e.g. a damaged PDF whose art spans more than the
             // canvas ("result would exceed the canvas"): an error is a fine outcome, a panic isn't.
-            let _ = s.execute("edit.paste", &json!({"center": [50, 50]}));
+            let _ = no_panic(s.execute("edit.paste", &json!({"center": [50, 50]})));
         }
     });
     prop_assert!(r.is_ok(), "{cmd}: panicked: {:?}", r.err());
@@ -1294,7 +1294,7 @@ proptest! {
         survive("hostile PostScript", || vectorcraft_engine::cmd::fileio::load("x.eps", ps.as_bytes()).ok().map(|l| l.doc))?;
         let r = catch_quiet(|| {
             let mut s = rich_session();
-            let _ = s.execute("file.place", &json!({"name": "x.eps", "dataBase64": vectorcraft_format::base64_encode(ps.as_bytes())}));
+            let _ = no_panic(s.execute("file.place", &json!({"name": "x.eps", "dataBase64": vectorcraft_format::base64_encode(ps.as_bytes())})));
         });
         r.map_err(|msg| TestCaseError::fail(format!("placing hostile PostScript panicked: {msg}")))?;
     }
@@ -1390,8 +1390,8 @@ proptest! {
         let r = catch_quiet(|| {
             let mut s = vectorcraft_engine::Session::new();
             let p = json!({"name": "x.pdf", "dataBase64": b64, "password": password});
-            let _ = s.execute("document.pdfInfo", &p);
-            if s.execute("document.open", &p).is_ok() {
+            let _ = no_panic(s.execute("document.pdfInfo", &p));
+            if no_panic(s.execute("document.open", &p)).is_ok() {
                 let d = (*s.doc().unwrap().doc).clone();
                 survive("encrypted pdf", || Some(d)).unwrap();
             }
@@ -1460,11 +1460,11 @@ fn survive_dxf(what: &str, bytes: &[u8], fit: bool) -> Result<(), TestCaseError>
     let _ = vectorcraft_cad::is_dxf(bytes);
     survive(what, || {
         let mut s = vectorcraft_engine::Session::new();
-        s.execute("file.new", &json!({"width": 300, "height": 200})).ok()?;
+        no_panic(s.execute("file.new", &json!({"width": 300, "height": 200}))).ok()?;
         let p = json!({"name": "x.dxf", "dataBase64": vectorcraft_format::base64_encode(bytes), "dxf": {"fit": fit}, "thumbnail": 8});
-        let _ = s.execute("file.place.info", &p);
-        let _ = s.execute("file.place", &p);
-        let _ = s.execute("document.dxfInfo", &p);
+        let _ = no_panic(s.execute("file.place.info", &p));
+        let _ = no_panic(s.execute("file.place", &p));
+        let _ = no_panic(s.execute("document.dxfInfo", &p));
         Some((*s.doc().ok()?.doc).clone())
     })
 }
@@ -1569,7 +1569,7 @@ fn survive_metafile(what: &str, name: &str, bytes: &[u8]) -> Result<(), TestCase
     let r = catch_quiet(|| {
         let mut s = vectorcraft_engine::Session::new();
         s.execute("file.new", &json!({"width": 100, "height": 100})).unwrap();
-        let _ = s.execute("file.place", &json!({"name": name, "dataBase64": vectorcraft_format::base64_encode(bytes)}));
+        let _ = no_panic(s.execute("file.place", &json!({"name": name, "dataBase64": vectorcraft_format::base64_encode(bytes)})));
     });
     prop_assert!(r.is_ok(), "{what}: placing panicked: {:?}", r.err());
     Ok(())