nix: stop module.nix writing the deprecated ephemeral key

Its default made headscale warn on every start. The camelCase rename now
targets node.ephemeral.inactivity_timeout, and the old path asserts.

CHANGELOG.md

@@ -87,6 +87,10 @@ removed on this schedule:
 - `--output json` / `--output yaml` now emit the API's shape — camelCase fields, string-encoded IDs, RFC3339 timestamps — instead of the old Protobuf encoding [#3324](https://github.com/juanfont/headscale/pull/3324)
 - `headscale policy` renames the database-bypass flag from `--bypass-grpc-and-access-database-directly` to `--bypass-server-and-access-database-directly` [#3324](https://github.com/juanfont/headscale/pull/3324)
 
+#### NixOS module
+
+- `settings.ephemeral_node_inactivity_timeout` is removed; set `settings.node.ephemeral.inactivity_timeout`, which headscale reads instead
+
 ### Changes
 
 - Expiring or deleting a non-existent pre-auth key now returns an error instead of silently succeeding [#3324](https://github.com/juanfont/headscale/pull/3324)

nix/module.nix

@@ -203,16 +203,6 @@ in
               };
             };
 
-            ephemeral_node_inactivity_timeout = lib.mkOption {
-              type = lib.types.str;
-              default = "30m";
-              description = ''
-                Time before an inactive ephemeral node is deleted.
-                Deprecated: use node.ephemeral.inactivity_timeout instead.
-              '';
-              example = "5m";
-            };
-
             node = {
               expiry = lib.mkOption {
                 type = lib.types.str;
@@ -629,7 +619,7 @@ in
     )
     (mkRenamedOptionModule
       [ "services" "headscale" "ephemeralNodeInactivityTimeout" ]
-      [ "services" "headscale" "settings" "ephemeral_node_inactivity_timeout" ]
+      [ "services" "headscale" "settings" "node" "ephemeral" "inactivity_timeout" ]
     )
     (mkRenamedOptionModule
       [ "services" "headscale" "logLevel" ]
@@ -710,6 +700,10 @@ in
         "oidc"
         "strip_email_domain"
       ] "The strip_email_domain option got removed upstream")
+      (assertRemovedOption [
+        "settings"
+        "ephemeral_node_inactivity_timeout"
+      ] "Use `node.ephemeral.inactivity_timeout` instead.")
     ];
 
     services.headscale.settings = lib.mkMerge [