fix(engine): hold a plugin's text.preview to the permissions of the command it previews (#1959)

* fix(engine): hold a plugin's text.preview to the permissions of the command it previews

* address review: check PREVIEWABLE before recursing into a preview's inner command

crates/engine/src/extensions/plugins.rs

@@ -149,6 +149,16 @@ fn refusal(m: &Manifest, command: &str, params: &Value) -> Option<String> {
     if DENIED.iter().any(|p| command.starts_with(p)) && !ALLOWED.contains(&command) {
         return Some(format!("`{command}` isn't available to plugins"));
     }
+    // A preview runs its inner command, which the plugin's permissions and the denied list must cover too.
+    // An inner command that can't be previewed (a nested preview) is refused by the preview itself,
+    // before it runs: descending into its parameters first would only rescan them.
+    if command == "text.preview"
+        && let Some(inner) = get(params, "command").and_then(Value::as_str)
+        && crate::textpreview::PREVIEWABLE.contains(&inner)
+        && let Some(why) = refusal(m, inner, get(params, "params").unwrap_or(&Value::Null))
+    {
+        return Some(why);
+    }
     // A widget's own data is FigCraft's to write, so no plugin can forge or retarget a widget.
     if writes_widget_data(params, 0) {
         return Some(format!("plugins can't write `{}…` layer data", crate::widgets::DATA_PREFIX));

crates/engine/src/plugins_tests.rs

@@ -153,6 +153,30 @@ fn read_only_plugins_and_allowlists_are_enforced() {
     assert_eq!(node(&s, a).name, "Rectangle");
 }
 
+#[test]
+fn a_preview_is_held_to_the_permissions_of_the_command_it_shows() {
+    let mut s = Session::new();
+    let a = rect(&mut s, 0.0);
+    // Only text.preview is allowed: the node.set it would run is not.
+    install(
+        &mut s,
+        manifest("org.test.previewer", "write", &["text.preview"]),
+        &script(&[("text.preview", json!({"command": "node.set", "params": {"id": a, "props": {"name": "x"}}}))], OnRefusal::Fail, ""),
+    );
+    let e = run_err(&mut s, "org.test.previewer");
+    assert!(e.contains("`node.set` isn't in the commands"), "{e}");
+    assert_eq!(node(&s, a).name, "Rectangle");
+}
+
+#[test]
+fn a_nested_preview_is_refused_by_the_preview_itself() {
+    let mut s = Session::new();
+    let nested = json!({"command": "text.preview", "params": {"command": "node.set", "params": {"props": {"name": "x"}}}});
+    install(&mut s, manifest("org.test.nested", "write", &["text.preview"]), &script(&[("text.preview", nested)], OnRefusal::Fail, ""));
+    let e = run_err(&mut s, "org.test.nested");
+    assert!(e.contains("can't be previewed"), "{e}");
+}
+
 #[test]
 fn files_dialogs_history_and_plugins_are_off_limits() {
     let mut s = Session::new();