require script is present during pack step iff any pkg procs are type script

backend/src/procedure/mod.rs

@@ -77,6 +77,12 @@ pub enum PackageProcedure {
     Script(JsProcedure),
 }
 impl PackageProcedure {
+    pub fn is_script(&self) -> bool {
+        match self {
+            Self::Js(_) => true,
+            _ => false,
+        }
+    }
     #[instrument]
     pub fn validate(
         &self,

backend/src/s9pk/manifest.rs

@@ -154,6 +154,29 @@ pub struct Manifest {
     pub dependencies: Dependencies,
 }
 
+impl Manifest {
+    pub fn package_procedures(&self) -> impl Iterator<Item = &PackageProcedure> {
+        use std::iter::once;
+        let main = once(&self.main);
+        let cfg_get = self.config.as_ref().map(|a| &a.get).into_iter();
+        let cfg_set = self.config.as_ref().map(|a| &a.set).into_iter();
+        let props = self.properties.iter();
+        let backups = vec![&self.backup.create, &self.backup.restore].into_iter();
+        let migrations = self
+            .migrations
+            .to
+            .values()
+            .chain(self.migrations.from.values());
+        let actions = self.actions.0.values().map(|a| &a.implementation);
+        main.chain(cfg_get)
+            .chain(cfg_set)
+            .chain(props)
+            .chain(backups)
+            .chain(migrations)
+            .chain(actions)
+    }
+}
+
 #[derive(Clone, Debug, Default, Deserialize, Serialize)]
 #[serde(rename_all = "kebab-case")]
 pub struct Assets {

backend/src/s9pk/mod.rs

@@ -13,7 +13,7 @@ use crate::s9pk::reader::S9pkReader;
 use crate::util::display_none;
 use crate::util::serde::IoFormat;
 use crate::volume::Volume;
-use crate::{Error, ResultExt};
+use crate::{Error, ErrorKind, ResultExt};
 
 pub mod builder;
 pub mod header;
@@ -123,8 +123,12 @@ pub async fn pack(#[context] ctx: SdkContext, #[arg] path: Option<PathBuf>) -> R
         })
         .scripts({
             let script_path = path.join(manifest.assets.scripts_path()).join("embassy.js");
-            if script_path.exists() {
-                Some(File::open(script_path).await?)
+            if manifest.package_procedures().any(|a| a.is_script()) {
+                if script_path.exists() {
+                    Some(File::open(script_path).await?)
+                } else {
+                    return Err(Error::new(eyre!("Script is declared in manifest, but no such script exists at ./scripts/embassy.js"), ErrorKind::Pack).into())
+                }
             } else {
                 None
             }