archetypes: build an archetype agent from its archetype's module on the hive

The hive reads the agent-archetype key when it provisions and rebuilds an
agent and keeps it in swarm-agent-archetypes.json. For an archetype agent
the meta flake has no agent-<name> input and mkAgent imports
hyperhive.hyperhiveArchetypes.<name>.module; provisioning, rebuilds, the
meta-input cascade, a deploy's rev and the startup migration skip the
config repos. The harness gets HIVE_ARCHETYPE and the system prompt says
the agent has no config repo. The create form sends the picked archetype.
Adds the android-dev built-in.

Refs #5386

hive-c0re/src/meta.rs

@@ -42,6 +42,9 @@ pub const CONTAINER_MANAGER_META_MOUNT: &str = "/meta";
 pub struct AgentSpec {
     pub name: String,
     pub port: u16,
+    /// The archetype the agent is built from (`crate::archetypes`), `None`
+    /// for a custom agent built from its own config repo.
+    pub archetype: Option<swarm_queue_client::agent_archetype::ArchetypeRef>,
 }
 
 /// Stage topology.json if it exists: it is regenerated by `reconcile`
@@ -786,6 +789,11 @@ where
     // (config PRs land there) but are not the flake's build input. deploy +
     // rebuild re-lock this input to `applied/<name>`'s current `main` head.
     for spec in agents {
+        // An archetype agent has no config repo, so no input: `mkAgent`
+        // takes its module from the archetype.
+        if spec.archetype.is_some() {
+            continue;
+        }
         let _ = writeln!(
             out,
             "    agent-{name}.url = \"git+file://{applied}\";",
@@ -811,17 +819,26 @@ where
     out.push_str("  };\n  outputs =\n    { self, hyperhive, ... }@inputs:\n    let\n");
     let _ = writeln!(
         out,
-        "      dashboardPort = {dashboard_port};\n      mkAgent = {{ name, port }}:"
+        "      dashboardPort = {dashboard_port};\n      mkAgent = {{ name, port, archetype ? null }}:"
     );
     out.push_str(
         r#"        let
           base = hyperhive.nixosConfigurations.agent-base;
-          input = inputs."agent-${name}";
+          # Every flake an archetype can come from, by its source name.
+          archetypeSources = { inherit hyperhive; };
+          agentModule =
+            if archetype == null then
+              inputs."agent-${name}".nixosModules.default
+            else
+              (archetypeSources.${archetype.source}
+                or (throw "agent ${name}: archetype source ${archetype.source} is not an input of this hive's meta flake")
+              ).hyperhiveArchetypes.${archetype.name}.module
+                or (throw "agent ${name}: this hive's ${archetype.source} input has no archetype ${archetype.name}; update that input");
           service = "hive-agent";
         in
         base.extendModules {
           modules = [
-            input.nixosModules.default
+            agentModule
             {
 "#,
     );
@@ -1008,6 +1025,10 @@ where
                 HYPERHIVE_HARNESS_DIR = "/agents/${name}/harness";
               };
             }
+            # Tells the harness the agent has no config repo of its own.
+            (if archetype == null then { } else {
+              systemd.services.${service}.environment.HIVE_ARCHETYPE = archetype.name;
+            })
           ];
         };
     in
@@ -1016,9 +1037,17 @@ where
 "#,
     );
     for spec in agents {
+        // `source` and `name` are identifiers (`archetypes::store_read`), so
+        // they need no escaping.
+        let archetype = spec.archetype.as_ref().map_or(String::new(), |a| {
+            format!(
+                " archetype = {{ source = \"{}\"; name = \"{}\"; }};",
+                a.source, a.name
+            )
+        });
         let _ = writeln!(
             out,
-            "        {} = mkAgent {{ name = \"{}\"; port = {}; }};",
+            "        {} = mkAgent {{ name = \"{}\"; port = {};{archetype} }};",
             spec.name, spec.name, spec.port,
         );
     }
@@ -1235,6 +1264,7 @@ mod tests {
         AgentSpec {
             name: name.to_owned(),
             port,
+            archetype: None,
         }
     }
 
@@ -1501,6 +1531,53 @@ mod tests {
         );
     }
 
+    /// An archetype agent has no `agent-<name>` input, and `mkAgent` is
+    /// handed its archetype; a custom agent beside it keeps its input.
+    #[test]
+    fn render_flake_builds_an_archetype_agent_from_its_archetype() {
+        let android = AgentSpec {
+            archetype: Some(swarm_queue_client::agent_archetype::ArchetypeRef {
+                source: "hyperhive".to_owned(),
+                name: "android-dev".to_owned(),
+            }),
+            ..sample_spec("droid", 9002)
+        };
+        let out = render_flake_with_lookup(
+            "github:example/hyperhive",
+            "path:/nix/store/bbbb-hyperhive-docs-source",
+            "path:/nix/store/aaaa-nixpkgs-source",
+            None,
+            8000,
+            &[sample_spec("alice", 9001), android],
+            |_| vec!["nixpkgs"],
+        );
+        assert!(
+            !out.contains("agent-droid"),
+            "an archetype agent has no config input:\n{out}"
+        );
+        assert!(
+            out.contains(
+                "droid = mkAgent { name = \"droid\"; port = 9002; \
+                 archetype = { source = \"hyperhive\"; name = \"android-dev\"; }; };"
+            ),
+            "{out}"
+        );
+        assert!(out.contains("agent-alice.url = \"git+file://"), "{out}");
+        assert!(out.contains("agent-alice.inputs.nixpkgs.follows"), "{out}");
+        assert!(
+            out.contains("alice = mkAgent { name = \"alice\"; port = 9001; };"),
+            "{out}"
+        );
+        assert!(
+            out.contains("hyperhiveArchetypes.${archetype.name}.module"),
+            "{out}"
+        );
+        assert!(
+            out.contains("environment.HIVE_ARCHETYPE = archetype.name"),
+            "{out}"
+        );
+    }
+
     #[test]
     fn render_flake_forwards_env_into_global_environment() {
         // Regression for the isolation breakage where forwarded vars