add a per-agent nix builds mode, host or none, carried like privateUsers

swarm-builder/src/push.rs

@@ -211,6 +211,7 @@ pub async fn cache_built(
             out_path,
             system,
             private_users,
+            nix_builds,
             ..
         },
     ) = (cache, &reply)
@@ -238,6 +239,7 @@ pub async fn cache_built(
                 system: system.clone(),
                 cached: true,
                 private_users: *private_users,
+                nix_builds: *nix_builds,
             }
         }
         Err(reason) => {
@@ -252,6 +254,8 @@ mod tests {
     use std::os::unix::fs::PermissionsExt as _;
     use std::sync::atomic::{AtomicBool, Ordering};
 
+    use hive_types::NixBuilds;
+
     use super::*;
 
     const TOKEN: &str = "eyJ0b2tlbiI6InNlY3JldCJ9.c2lnbmVk";
@@ -263,6 +267,7 @@ mod tests {
             system: "x86_64-linux".to_owned(),
             cached: false,
             private_users: false,
+            nix_builds: NixBuilds::Disabled,
         }
     }
 
@@ -294,6 +299,17 @@ mod tests {
         let cache = cache_with("true");
         let reply = cache_built(built(), Some(&cache), token(), PUSH_DEADLINE, "atlas").await;
         assert!(cached(&reply), "{reply:?}");
+        // The rewritten reply keeps what the evaluated config said.
+        assert!(
+            matches!(
+                reply,
+                FromMetaReply::Built {
+                    nix_builds: NixBuilds::Disabled,
+                    ..
+                }
+            ),
+            "{reply:?}"
+        );
     }
 
     #[tokio::test]