diff --git a/crates/engine/tests/hostile_params.rs b/crates/engine/tests/hostile_params.rs
new file mode 100644
index 00000000..b7769239
--- /dev/null
+++ b/crates/engine/tests/hostile_params.rs
@@ -0,0 +1,104 @@
+//! Every command survives hostile parameters (what an agent or a buggy script might send).
+
+use proptest::prelude::*;
+use serde_json::{Value, json};
+
+const KEYS: &[&str] = &[
+    "track",
+    "tracks",
+    "start",
+    "end",
+    "at",
+    "length",
+    "clip",
+    "clips",
+    "db",
+    "delta_db",
+    "value",
+    "pan",
+    "count",
+    "ratio",
+    "bpm",
+    "format",
+    "slot",
+    "param",
+    "plugin",
+    "mode",
+    "tool",
+    "kind",
+    "name",
+    "index",
+    "number",
+    "semitones",
+    "by",
+    "to",
+    "grid",
+    "height",
+    "view",
+    "color",
+    "params",
+    "process",
+    "group",
+    "bus",
+    "input",
+    "output",
+    "numerator",
+    "denominator",
+    "factor",
+    "sensitivity",
+    "rating",
+    "direction",
+    "seconds",
+    "frames",
+    "samples",
+    "notes",
+    "pitch",
+    "velocity",
+    "flag",
+];
+
+fn hostile_value() -> impl Strategy<Value = Value> {
+    prop_oneof![
+        Just(json!(null)),
+        Just(json!(-1)),
+        Just(json!(0)),
+        Just(json!(i64::MAX)),
+        Just(json!(i64::MIN)),
+        Just(json!(1.0e308)),
+        Just(json!(-1.0e308)),
+        Just(json!(0.5)),
+        Just(json!("")),
+        Just(json!("Kick")),
+        Just(json!("bars_beats:9999999|99|9999")),
+        Just(json!("\u{0}\u{fffd}")),
+        Just(json!([])),
+        Just(json!([1, "Kick", null, -5])),
+        Just(json!({})),
+        Just(json!({"seconds": -1e12})),
+        Just(json!({"a": 1})),
+        Just(json!(true)),
+    ]
+}
+
+proptest! {
+    #![proptest_config(ProptestConfig { cases: 8, .. ProptestConfig::default() })]
+    #[test]
+    fn no_command_panics_on_hostile_params(fields in proptest::collection::vec((0usize..KEYS.len(), hostile_value()), 0..6)) {
+        let mut params = serde_json::Map::new();
+        for (k, v) in fields {
+            params.insert(KEYS[k].to_string(), v);
+        }
+        let params = Value::Object(params);
+        for spec in soundcraft_engine::command_specs() {
+            // Commands that write files take paths; keep the test hermetic.
+            if spec.params.contains("path") || spec.params.contains("dir") || spec.id == "app.quit" {
+                continue;
+            }
+            let mut e = soundcraft_engine::demo::demo_engine();
+            let _ = e.execute("edit.select", &json!({"tracks": ["Kick", "Keys"], "start": 100_000, "end": 600_000}));
+            if let Err(soundcraft_engine::EngineError::Internal(id, msg)) = e.execute(spec.id, &params) {
+                prop_assert!(false, "{id} panicked with {params}: {msg}");
+            }
+        }
+    }
+}