set useAcmehost to null

sops-nix's default identity discovery imports the host's SSH
ed25519 key as an age identity, but secrets/tide.yaml is encrypted
to the age key generated with age-keygen and stored at
/var/lib/sops-nix/key.txt. Without sops.age.keyFile pointing at
that path, activation fails with 'Error getting data key: 0
successful groups required, got 0'. Also blank the SSH/GPG
fallback paths so the module never silently picks up an
unintended identity.

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -1,2 +1,3 @@
 *~
-result
+result
+/.direnv/

tide.nix

@@ -11,7 +11,7 @@
     # Reuse the wildcard cert already issued for *.${domainName}
     # in configuration.nix instead of requesting a new one per
     # subdomain.
-    nginx.useACMEHost = domainName;
+    nginx.useACMEHost = null;
   };
 
   # Don't fail evaluation when secrets/tide.yaml is missing (e.g.
@@ -20,6 +20,14 @@
   # the file is absent, which is the right place for that failure.
   sops.validateSopsFiles = false;
 
+  # Use the host's age key generated with age-keygen, not the
+  # SSH-host-key-derived identity sops-nix falls back to by default.
+  # The encrypted file's recipient is the public key paired with
+  # this private key.
+  sops.age.keyFile = "/var/lib/sops-nix/key.txt";
+  sops.age.sshKeyPaths = [ ];
+  sops.gnupg.sshKeyPaths = [ ];
+
   sops.secrets."tide-env" = {
     sopsFile = ./secrets/tide.yaml;
     # phpfpm reads this via EnvironmentFile, which runs as root