feat(mesh-phase4): driver-only node must be FetchAndCache (validator)

Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW

src/Core/ZB.MOM.WW.OtOpcUa.Cluster/ConfigSourceOptionsValidator.cs

@@ -1,3 +1,4 @@
+using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.Options;
 
 namespace ZB.MOM.WW.OtOpcUa.Cluster;
@@ -14,6 +15,20 @@ namespace ZB.MOM.WW.OtOpcUa.Cluster;
 /// </remarks>
 public sealed class ConfigSourceOptionsValidator : IValidateOptions<ConfigSourceOptions>
 {
+    private readonly IConfiguration _configuration;
+
+    /// <summary>
+    ///     DI-constructed by <c>AddValidatedOptions</c> (a plain <c>AddSingleton</c>), so a
+    ///     constructor dependency is safe here. <see cref="IConfiguration"/> — not
+    ///     <c>IClusterRoleInfo</c> — is the source of this node's roles: <c>IClusterRoleInfo</c>'s
+    ///     implementation needs the <c>ActorSystem</c>, which does not exist yet at
+    ///     <c>ValidateOnStart</c> time.
+    /// </summary>
+    public ConfigSourceOptionsValidator(IConfiguration configuration)
+    {
+        _configuration = configuration;
+    }
+
     /// <inheritdoc />
     public ValidateOptionsResult Validate(string? name, ConfigSourceOptions options)
     {
@@ -76,6 +91,24 @@ public sealed class ConfigSourceOptionsValidator : IValidateOptions<ConfigSource
             }
         }
 
+        // Per-cluster mesh Phase 4: a driver-only node has no central ConfigDb connection to fall back
+        // on, so Direct is only ever valid on a fused admin+driver node (admin holds the SQL
+        // connection). Roles come from Cluster:Roles directly, not IClusterRoleInfo — see the ctor
+        // remark.
+        var roles = _configuration.GetSection("Cluster:Roles").Get<string[]>() ?? Array.Empty<string>();
+        var isDriver = Array.IndexOf(roles, "driver") >= 0;
+        var isAdmin = Array.IndexOf(roles, "admin") >= 0;
+
+        if (isDriver && !isAdmin && isDirect)
+        {
+            errors.Add(
+                "Cluster:Roles is a driver-only node (has 'driver', not 'admin') but "
+                + $"{ConfigSourceOptions.SectionName}:{nameof(ConfigSourceOptions.Mode)} is 'Direct'. A "
+                + "driver-only node has no central ConfigDb to read from — it must use 'FetchAndCache'. "
+                + $"Set {ConfigSourceOptions.SectionName}:{nameof(ConfigSourceOptions.Mode)}="
+                + $"{ConfigSourceOptions.ModeFetchAndCache} (see docs/Configuration.md → ConfigSource).");
+        }
+
         return errors.Count == 0
             ? ValidateOptionsResult.Success
             : ValidateOptionsResult.Fail(string.Join(" ", errors));