agents: drop root, run as per-agent unix user with passwordless sudo (#658)

nix/templates/agent-base.nix

@@ -1,4 +1,7 @@
 { pkgs, config, ... }:
+let
+  userName = config.hyperhive.user.name;
+in
 {
   imports = [ ./harness-base.nix ];
 
@@ -15,6 +18,11 @@
     path = [ "/run/current-system/sw" ];
     environment = {
       SHELL = "${pkgs.bashInteractive}/bin/bash";
+      # `HOME` defaults to `/` for systemd services without a User=
+      # set. With #658 the harness runs as the agent user — set HOME
+      # explicitly so claude (which the harness spawns) finds its
+      # `~/.claude/` session dir at the bind-mounted location.
+      HOME = "/home/${userName}";
       # Path to the merged agent static dist. The harness serves this
       # via `tower_http::ServeDir` for any request it doesn't route to
       # an API endpoint. `mergedDist` is the agent-default dist with
@@ -30,6 +38,14 @@
       ExecStart = "${pkgs.hyperhive}/bin/hive-ag3nt serve";
       Restart = "on-failure";
       RestartSec = 2;
+      # Run the harness as the per-agent user (#658). claude itself
+      # spawned by the harness then runs as that user too — drops
+      # root inside the container while sudo (`NOPASSWD: ALL` by
+      # default, see harness-base.nix `hyperhive.user.passwordlessSudo`)
+      # keeps the previous root-by-default surface available
+      # explicitly for tools that need it.
+      User = userName;
+      Group = userName;
     };
   };
 }