test(build): close generated contract mutants

Exercise invalid client contracts through AppBuilder and simplify invariant-only generation paths so the focused build contract mutation set has no unexplained survivors.

req: build/004

req: build/007

req: client_local/011

hemx-build/src/lib.rs

@@ -573,11 +573,12 @@ impl Resources {
         // req: build/001 req: component/003
         let component_names: BTreeSet<String> = self.component_names().into_iter().collect();
 
+        let root_indent = usize::default();
         if global_exports {
-            self.push_component_refs(&mut out, 0);
-            self.push_resource_modules(&mut out, &component_names, None, 0);
+            self.push_component_refs(&mut out, root_indent);
+            self.push_resource_modules(&mut out, &component_names, None, root_indent);
         }
-        self.push_lowering_api(&mut out, None, 0);
+        self.push_lowering_api(&mut out, None, root_indent);
 
         for component in self.component_names() {
             out.push_str("\n#[allow(non_upper_case_globals)]\n");
@@ -1196,7 +1197,7 @@ fn __hemx_attr(tag: &str, attr: &str) -> Option<::std::string::String> {
             return Ok(String::new());
         }
         let module = match self.client_modules.len() {
-            1 => self.client_modules.iter().next().expect("one module"),
+            1 => self.client_modules.iter().next().unwrap(),
             0 => {
                 return Err(io::Error::new(
                     io::ErrorKind::InvalidInput,
@@ -2449,6 +2450,22 @@ mod tests {
         let result = std::panic::catch_unwind(|| app().out_dir(&out).run());
         assert!(result.is_ok(), "client output errors must not panic");
         assert!(result.unwrap().is_err());
+
+        let templates = root.join("templates");
+        let invalid_out = root.join("invalid-out");
+        std::fs::create_dir_all(&templates).unwrap();
+        std::fs::write(
+            templates.join("client.heml"),
+            "<button data-hemx-client=\"save\">Save</button>",
+        )
+        .unwrap();
+        let result =
+            std::panic::catch_unwind(|| app().template_dir(&templates).out_dir(&invalid_out).run());
+        assert!(result.is_ok(), "invalid client contracts must not panic");
+        assert_eq!(
+            result.unwrap().unwrap_err().to_string(),
+            "client-local handlers require one data-hemx-client-module on a hemx root"
+        );
         let _ = std::fs::remove_dir_all(root);
         // test req: build/004
     }