feat(instance): the basics say when GitHub sign-in ends

ADR 0017, D2: GitHub sign-in is deprecated. Where the operator set
`GITHUB_SIGN_IN_ENDS`, `instance.basics()` names the day until it has
come, so apps can tell people who sign in with GitHub to add an
address, a password and an authenticator before then.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_base_client/lib/src/protocol/client.dart

@@ -229,9 +229,8 @@ class EndpointInstance extends _isc.EndpointRef {
   /// operator's OAuth app and until it ends (ADR 0017), email sign-in only
   /// where the register can mail codes (this server, or on a member the
   /// register, ADR 0016), password sign-in where the register holds its
-  /// keys, where its
-  /// source is, the oldest app build it works with, and where it keeps
-  /// people's data and its backups.
+  /// keys, when GitHub sign-in ends, where its source is, the oldest app
+  /// build it works with, and where it keeps people's data and its backups.
   _ida.Future<_isnyur2i.InstanceBasics> basics() =>
       caller.callServerEndpoint<_isnyur2i.InstanceBasics>(
         'halkyon_base.instance',

packages/halkyon_base_client/lib/src/protocol/instance/instance_basics.dart

@@ -27,6 +27,7 @@ abstract class InstanceBasics
     this.dataLocation,
     this.backupLocation,
     bool? passwordSignIn,
+    this.gitHubSignInEnds,
   }) : passwordSignIn = passwordSignIn ?? false;
 
   factory InstanceBasics({
@@ -38,6 +39,7 @@ abstract class InstanceBasics
     String? dataLocation,
     String? backupLocation,
     bool? passwordSignIn,
+    DateTime? gitHubSignInEnds,
   }) = _InstanceBasicsImpl;
 
   factory InstanceBasics.fromJson(Map<String, dynamic> jsonSerialization) {
@@ -56,6 +58,11 @@ abstract class InstanceBasics
           : _isc.BoolJsonExtension.fromJson(
               jsonSerialization['passwordSignIn'],
             ),
+      gitHubSignInEnds: jsonSerialization['gitHubSignInEnds'] == null
+          ? null
+          : _isc.DateTimeJsonExtension.fromJson(
+              jsonSerialization['gitHubSignInEnds'],
+            ),
     );
   }
 
@@ -93,6 +100,12 @@ abstract class InstanceBasics
   /// operator set the keys it needs.
   bool passwordSignIn;
 
+  /// When GitHub sign-in ends here (ADR 0017: it is deprecated), as its
+  /// operator set it (GITHUB_SIGN_IN_ENDS), in UTC; null while no end is set,
+  /// or once it has ended. People who sign in with GitHub add an address, a
+  /// password and an authenticator before then.
+  DateTime? gitHubSignInEnds;
+
   /// Returns a shallow copy of this [InstanceBasics]
   /// with some or all fields replaced by the given arguments.
   @_isc.useResult
@@ -105,6 +118,7 @@ abstract class InstanceBasics
     String? dataLocation,
     String? backupLocation,
     bool? passwordSignIn,
+    DateTime? gitHubSignInEnds,
   });
   @override
   Map<String, dynamic> toJson() {
@@ -118,6 +132,8 @@ abstract class InstanceBasics
       if (dataLocation != null) 'dataLocation': dataLocation,
       if (backupLocation != null) 'backupLocation': backupLocation,
       'passwordSignIn': passwordSignIn,
+      if (gitHubSignInEnds != null)
+        'gitHubSignInEnds': gitHubSignInEnds?.toJson(),
     };
   }
 
@@ -133,6 +149,8 @@ abstract class InstanceBasics
       if (dataLocation != null) 'dataLocation': dataLocation,
       if (backupLocation != null) 'backupLocation': backupLocation,
       'passwordSignIn': passwordSignIn,
+      if (gitHubSignInEnds != null)
+        'gitHubSignInEnds': gitHubSignInEnds?.toJson(),
     };
   }
 
@@ -154,6 +172,7 @@ class _InstanceBasicsImpl extends InstanceBasics {
     String? dataLocation,
     String? backupLocation,
     bool? passwordSignIn,
+    DateTime? gitHubSignInEnds,
   }) : super._(
          app: app,
          gitHubClientId: gitHubClientId,
@@ -163,6 +182,7 @@ class _InstanceBasicsImpl extends InstanceBasics {
          dataLocation: dataLocation,
          backupLocation: backupLocation,
          passwordSignIn: passwordSignIn,
+         gitHubSignInEnds: gitHubSignInEnds,
        );
 
   /// Returns a shallow copy of this [InstanceBasics]
@@ -178,6 +198,7 @@ class _InstanceBasicsImpl extends InstanceBasics {
     Object? dataLocation = _Undefined,
     Object? backupLocation = _Undefined,
     bool? passwordSignIn,
+    Object? gitHubSignInEnds = _Undefined,
   }) {
     return InstanceBasics(
       app: app ?? this.app,
@@ -192,6 +213,9 @@ class _InstanceBasicsImpl extends InstanceBasics {
           ? backupLocation
           : this.backupLocation,
       passwordSignIn: passwordSignIn ?? this.passwordSignIn,
+      gitHubSignInEnds: gitHubSignInEnds is DateTime?
+          ? gitHubSignInEnds
+          : this.gitHubSignInEnds,
     );
   }
 }