refactor(beszel): move KEY and TOKEN fully into enable-agent.nix

KEY (hub's SSH public key) is now stored in variables.nix as beszelHubKey
and set by enable-agent.nix — no host file ever needs to touch it.
TOKEN was already universal; this removes the last per-host beszel config.

Importing enable-agent.nix in a build type is now the only step needed to
add a new host to beszel monitoring.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -21,8 +21,7 @@ machines when deployed.
   `modules/installer/common.nix` (the auto-installer's own root/nixos login —
   a deliberate, documented choice, see `docs/auto-installer.md`, not
   accidental tech debt) and **SSH public keys** in `variables.nix`
-  (`vars.adminSshKey`, `vars.remoteBuilderAuthorizedKeys`) plus per-host
+  (`vars.adminSshKey`, `vars.remoteBuilderAuthorizedKeys`, `vars.beszelHubKey`). Don't use the installer's hardcoded hash as a
-  `KEY` values for beszel-agent auth (see `docs/beszel.md`). Don't use the installer's hardcoded hash as a
   template for a *real* host — every other host uses sops-nix
   (`hashedPasswordFile`, see "Security Notes" in `README.md`). Flag any *new*
   secret-like string you encounter instead of committing it.

docs/beszel.md

@@ -14,13 +14,16 @@ Everything is handled by a single module:
 **`modules/beszel/enable-agent.nix`** — imported by a build type. It:
 - Enables `beszel-agent`
 - Sets `HUB_URL` to `docker.sweet.home:8090`
-- Reads the universal `beszel-token` from `secrets/common.yaml` via sops and
+- Sets `KEY` from `vars.beszelHubKey` (`variables.nix`) — the hub's SSH
-  passes it to the agent as `TOKEN` in an env file
+  public key, shared by every agent. Update `beszelHubKey` if the docker
+  host is ever rebuilt and the hub generates a new keypair.
+- Reads the universal `beszel-token` from `secrets/common.yaml` via sops
+  and passes it to the agent as `TOKEN` in an env file
 - Fixes an upstream bug where the agent couldn't persist its hub-pairing
   fingerprint across restarts (adds a real `StateDirectory`)
 
-The only thing a host file ever needs to add is `KEY` — the hub's public key
+A host file needs no beszel configuration at all — just import the module
-for that agent slot, which comes from the beszel hub UI after first pairing.
+in the build type and add the system in the hub UI.
 
 ---
 
@@ -36,30 +39,23 @@ imports = [
 ];
 ```
 
-That's the only build-type change required.
+That's the only change required. The host file needs nothing.
 
 ---
 
-## Wiring the host file
+## Adding a new system to the hub
 
-No `imports` are needed in the host file. Just set `KEY` once you've paired
+1. Rebuild and deploy the host with its build type importing `enable-agent.nix`.
-the agent with the hub:
+2. Open the beszel hub (`http://docker.sweet.home:8090`).
-
+3. Go to **Systems → Add system**, enter the host's IP and the default port
-```nix
+   (45876). The agent will connect and the system will appear as active.
-services.beszel.agent.environment = {
-  KEY = "ssh-ed25519 AAAA...";
-};
-```
-
-Leave `KEY` commented out until after the first pairing (see "Pairing with
-the hub" below).
 
 ---
 
 ## One-time setup: add the token to `secrets/common.yaml`
 
 The universal token is stored once in the common secrets file, shared by all
-agents. You only need to do this once, not per-host:
+agents. Only needed once, not per-host:
 
 ```sh
 sops secrets/common.yaml
@@ -67,26 +63,21 @@ sops secrets/common.yaml
 
 Add:
 ```yaml
-beszel-token: <token from the beszel hub UI>
+beszel-token: <token from the beszel hub Settings → Keys>
 ```
 
-The token is found in the beszel hub under **Settings → Keys** or in the
-"Add system" flow.
-
 `secrets/common.yaml` is already a sops recipient for every host via their
-SSH host keys, so no additional sops recipient setup is needed for hosts that
+SSH host keys, so no additional sops recipient setup is needed.
-are already provisioned.
 
 ---
 
 ## Optional: monitoring extra filesystems
 
 To report disk usage for a mount beyond the root filesystem, add
-`EXTRA_FILESYSTEMS` alongside `KEY` in the host file:
+`EXTRA_FILESYSTEMS` in the host file:
 
 ```nix
 services.beszel.agent.environment = {
-  KEY = "ssh-ed25519 AAAA...";
   EXTRA_FILESYSTEMS = "/mnt/data";   # colon-separated for multiple paths
 };
 ```
@@ -94,7 +85,10 @@ services.beszel.agent.environment = {
 The `server` host uses this to expose its ZFS data pool:
 
 ```nix
+services.beszel.agent.environment = {
   EXTRA_FILESYSTEMS = "${vars.storageRoot}/${vars.nfsShares.dockerVolumes.subpath}";
+  LOG_LEVEL = "debug";
+};
 ```
 
 ---
@@ -112,44 +106,8 @@ stats. Hosts without Docker should leave it commented out.
 
 ---
 
-## Pairing with the hub
+## If the hub key changes
 
-1. Deploy the host with its build type importing `enable-agent.nix`. Leave
+If the docker host is ever rebuilt and beszel generates a new SSH keypair,
-   `KEY` unset (commented out) for now.
+update `beszelHubKey` in `variables.nix` and rebuild all beszel-enabled hosts.
-2. Open the beszel hub (`http://docker.sweet.home:8090`).
+The new key is visible in the beszel hub under **Settings → Keys**.
-3. Go to **Systems → Add system**. The new host should appear as an unpaired
-   entry — copy the `KEY` value shown there.
-4. In `hosts/<name>/host.nix`, set:
-   ```nix
-   services.beszel.agent.environment.KEY = "<copied key>";
-   ```
-5. Rebuild and deploy the host. The agent will now pair permanently.
-
----
-
-## Example: complete host file
-
-Minimal case (`hosts/tor-relay/host.nix` — one filesystem, no Docker, LXC):
-
-```nix
-{ vars, ... }:
-{
-  networking = { ... };
-
-  services.beszel.agent.environment = {
-    KEY = "ssh-ed25519 AAAA...";
-  };
-
-  system.stateVersion = "26.05";
-}
-```
-
-Fuller case (`hosts/server/host.nix` — extra filesystem, debug logging):
-
-```nix
-services.beszel.agent.environment = {
-  KEY = "ssh-ed25519 AAAA...";
-  EXTRA_FILESYSTEMS = "${vars.storageRoot}/${vars.nfsShares.dockerVolumes.subpath}";
-  LOG_LEVEL = "debug";
-};
-```

hosts/ha-server-1/host.nix

@@ -16,8 +16,5 @@
     nameservers = [ vars.domainControllerIp ];
   };
 
-  # Set KEY after pairing this host with the beszel hub (see docs/beszel.md).
-  # services.beszel.agent.environment.KEY = "";
-
   system.stateVersion = "26.05";
 }

hosts/ha-server-2/host.nix

@@ -16,8 +16,5 @@
     nameservers = [ vars.domainControllerIp ];
   };
 
-  # Set KEY after pairing this host with the beszel hub (see docs/beszel.md).
-  # services.beszel.agent.environment.KEY = "";
-
   system.stateVersion = "26.05";
 }

hosts/nix-cache/host.nix

@@ -12,10 +12,6 @@
     nameservers = [ vars.domainControllerIp ];
   };
 
-  services.beszel.agent.environment = {
-    KEY = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFPR9kwtC4TAeTRu46A7+opZsYpxqkRJ+x/ZyB2GWCeG";
-  };
-
   # Preserved from the pre-refactor `nix-cache` target — stateVersion must
   # never be bumped on an already-installed machine.
   system.stateVersion = "25.05";

hosts/server/host.nix

@@ -14,7 +14,6 @@
   };
 
   services.beszel.agent.environment = {
-    KEY = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFPR9kwtC4TAeTRu46A7+opZsYpxqkRJ+x/ZyB2GWCeG";
     EXTRA_FILESYSTEMS = "${vars.storageRoot}/${vars.nfsShares.dockerVolumes.subpath}";
     LOG_LEVEL = "debug";
   };

hosts/tailscale-router/host.nix

@@ -12,10 +12,6 @@
     nameservers = [ vars.domainControllerIp ];
   };
 
-  services.beszel.agent.environment = {
-    KEY = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFPR9kwtC4TAeTRu46A7+opZsYpxqkRJ+x/ZyB2GWCeG";
-  };
-
   # No networking.hostId: only ZFS-touching hosts (server, docker) need one
   # for pool-import safety, and this host does neither.
 

hosts/tor-relay/host.nix

@@ -15,10 +15,6 @@
   # No networking.hostId: only ZFS-touching hosts need one for pool-import
   # safety, and this host does neither.
 
-  services.beszel.agent.environment = {
-    KEY = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFPR9kwtC4TAeTRu46A7+opZsYpxqkRJ+x/ZyB2GWCeG";
-  };
-
   # A genuinely new host (not a pre-refactor carry-over), so it tracks the
   # flake's current nixpkgs release rather than being pinned to an older one.
   system.stateVersion = "26.05";

modules/beszel/enable-agent.nix

@@ -16,6 +16,7 @@
     environment = {
       #DOCKER_HOST = "tcp://docker-socket-proxy:2375";
       HUB_URL = "http://${vars.dockerHost}.${vars.homeDomain}:${toString vars.ports.beszelHub}";
+      KEY = vars.beszelHubKey;
     };
   };
 

variables.nix

@@ -40,6 +40,11 @@
   # from scratch.
   nixCacheHostKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAICuHUxGNH6ei3BZD+EfZs3l4X8uJNcjQiOsM/G4yo4O/ lxc-nix-cache";
 
+  # Beszel hub's SSH public key — used by every agent to authenticate the
+  # hub's incoming connection. Update if the docker host is ever rebuilt and
+  # the hub generates a new keypair.
+  beszelHubKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFPR9kwtC4TAeTRu46A7+opZsYpxqkRJ+x/ZyB2GWCeG";
+
   # Public keys authorized to SSH in as remoteBuilderUser on the nix-cache
   # host (modules/nix-cache/server.nix) — one per client host that's allowed
   # to use it as a distributed builder.