fix(options): validate Host Node/Database/Logging options at startup — empty NodeName fails fast instead of NULLing SourceNode (plan R2-08 T7, arch-review 08r2 NF4)

src/ZB.MOM.WW.ScadaBridge.Host/LoggingOptionsValidator.cs

@@ -0,0 +1,27 @@
+using Serilog.Events;
+using ZB.MOM.WW.Configuration;
+
+namespace ZB.MOM.WW.ScadaBridge.Host;
+
+/// <summary>
+/// Validates <see cref="LoggingOptions"/> at host startup (arch-review 08 round
+/// 2 NF4). <see cref="LoggingOptions.MinimumLevel"/> is parsed into a Serilog
+/// <see cref="LogEventLevel"/> by <c>LoggerConfigurationFactory.ParseLevel</c>,
+/// which silently falls back to <c>Information</c> for an unrecognised value.
+/// This validator surfaces that misconfiguration at boot instead: a present,
+/// non-blank value must name a real level (Verbose/Debug/Information/Warning/
+/// Error/Fatal, case-insensitive). A null/blank value is treated as "unset"
+/// (defaults to Information), mirroring the parser.
+/// </summary>
+public sealed class LoggingOptionsValidator : OptionsValidatorBase<LoggingOptions>
+{
+    /// <inheritdoc />
+    protected override void Validate(ValidationBuilder builder, LoggingOptions options)
+    {
+        builder.RequireThat(
+            string.IsNullOrWhiteSpace(options.MinimumLevel)
+                || Enum.TryParse<LogEventLevel>(options.MinimumLevel, ignoreCase: true, out _),
+            $"ScadaBridge:Logging:{nameof(LoggingOptions.MinimumLevel)} ('{options.MinimumLevel}') " +
+            $"is not a recognised Serilog level. Valid: {string.Join(", ", Enum.GetNames<LogEventLevel>())}.");
+    }
+}