Normalize scalar frontmatter lists

MeetingAssistant/MeetingNotes/FrontmatterYamlDeserializer.cs

@@ -0,0 +1,24 @@
+using YamlDotNet.Serialization;
+using YamlDotNet.Serialization.NamingConventions;
+
+namespace MeetingAssistant.MeetingNotes;
+
+internal static class FrontmatterYamlDeserializer
+{
+    public static IDeserializer Create()
+    {
+        return new DeserializerBuilder()
+            .WithTypeConverter(new ScalarStringListYamlTypeConverter())
+            .IgnoreUnmatchedProperties()
+            .Build();
+    }
+
+    public static IDeserializer CreateWithUnderscoredNaming()
+    {
+        return new DeserializerBuilder()
+            .WithNamingConvention(UnderscoredNamingConvention.Instance)
+            .WithTypeConverter(new ScalarStringListYamlTypeConverter())
+            .IgnoreUnmatchedProperties()
+            .Build();
+    }
+}

MeetingAssistant/MeetingNotes/MarkdownMeetingNoteStore.cs

@@ -16,9 +16,7 @@ public sealed class MarkdownMeetingNoteStore : IMeetingNoteStore
     {
         this.options = options.Value;
         this.logger = logger;
-        yamlDeserializer = new DeserializerBuilder()
-            .IgnoreUnmatchedProperties()
-            .Build();
+        yamlDeserializer = FrontmatterYamlDeserializer.Create();
     }
 
     public async Task<MeetingNote> SaveAsync(MeetingNote note, CancellationToken cancellationToken)

MeetingAssistant/MeetingNotes/ScalarStringListYamlTypeConverter.cs

@@ -0,0 +1,38 @@
+using YamlDotNet.Core;
+using YamlDotNet.Core.Events;
+using YamlDotNet.Serialization;
+
+namespace MeetingAssistant.MeetingNotes;
+
+internal sealed class ScalarStringListYamlTypeConverter : IYamlTypeConverter
+{
+    public bool Accepts(Type type)
+    {
+        return type == typeof(List<string>);
+    }
+
+    public object ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeserializer)
+    {
+        if (parser.TryConsume<Scalar>(out var scalar))
+        {
+            return string.IsNullOrWhiteSpace(scalar.Value)
+                ? []
+                : new List<string> { scalar.Value };
+        }
+
+        var values = new List<string>();
+        parser.Consume<SequenceStart>();
+        while (!parser.TryConsume<SequenceEnd>(out _))
+        {
+            var item = parser.Consume<Scalar>();
+            values.Add(item.Value);
+        }
+
+        return values;
+    }
+
+    public void WriteYaml(IEmitter emitter, object? value, Type type, ObjectSerializer serializer)
+    {
+        serializer(value, typeof(IEnumerable<string>));
+    }
+}