test the archetype module import in the meta flake render; update archetypes doc

hive-meta-flake/src/lib.rs

@@ -617,6 +617,55 @@ mod tests {
         assert!(!builds_agent_at(&flake, "ghost", Some(&reviewer()), None));
     }
 
+    /// The text of `mkAgent`'s `let` binding `name`: from `name =` to the
+    /// next binding at the same indent (`;` ends it at line end).
+    fn binding<'a>(flake: &'a str, name: &str) -> &'a str {
+        let from = flake
+            .find(&format!("\n          {name} =\n"))
+            .or_else(|| flake.find(&format!("\n          {name} = ")))
+            .unwrap_or_else(|| panic!("no `{name}` binding in mkAgent"));
+        let rest = &flake[from + 1..];
+        let end = rest
+            .find("\n          service =")
+            .unwrap_or_else(|| panic!("`{name}` is the last binding"));
+        &rest[..end]
+    }
+
+    #[test]
+    fn an_archetype_agent_s_module_is_the_archetype_source_s_module() {
+        let flake = rendered();
+        let module = binding(&flake, "agentModule");
+        assert!(
+            module.contains("archetypeSources.${archetype.source}"),
+            "the archetype branch picks its source by name: {module}"
+        );
+        assert!(
+            module.contains(".hyperhiveArchetypes.${archetype.name}.module"),
+            "the archetype branch imports the archetype's module: {module}"
+        );
+        // The source it picks from must offer the hyperhive input.
+        assert!(
+            binding(&flake, "archetypeSources").contains("inherit hyperhive;"),
+            "the `hyperhive` archetype source"
+        );
+        // The module reaches the agent's system.
+        let modules = &flake[flake.find("modules = [").expect("a module list")..];
+        assert!(
+            modules
+                .trim_start_matches("modules = [")
+                .trim_start()
+                .starts_with("agentModule"),
+            "agentModule heads the extendModules list"
+        );
+        // The entry names the source and archetype the import reads.
+        assert!(
+            flake.contains("rev = mkAgent { name = \"rev\"; port = ")
+                && flake
+                    .contains(" archetype = { source = \"hyperhive\"; name = \"reviewer\"; }; };"),
+            "the archetype agent's entry"
+        );
+    }
+
     #[test]
     fn an_agent_whose_name_ends_another_s_is_not_that_agent() {
         let flake = rendered();