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src/Scanner/__Libraries/StellaOps.Scanner.CallGraph/Serialization/ImmutableArrayJsonConverter.cs

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+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace StellaOps.Scanner.CallGraph.Serialization;
+
+/// <summary>
+/// System.Text.Json converter for <see cref="ImmutableArray{T}"/> to ensure default serializer options
+/// can round-trip call graph models without requiring per-call JsonSerializerOptions registration.
+/// </summary>
+public sealed class ImmutableArrayJsonConverter<T> : JsonConverter<ImmutableArray<T>>
+{
+    public override ImmutableArray<T> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        if (reader.TokenType == JsonTokenType.Null)
+        {
+            return ImmutableArray<T>.Empty;
+        }
+
+        var values = JsonSerializer.Deserialize<List<T>>(ref reader, options);
+        if (values is null || values.Count == 0)
+        {
+            return ImmutableArray<T>.Empty;
+        }
+
+        return ImmutableArray.CreateRange(values);
+    }
+
+    public override void Write(Utf8JsonWriter writer, ImmutableArray<T> value, JsonSerializerOptions options)
+    {
+        writer.WriteStartArray();
+
+        var normalized = value.IsDefault ? ImmutableArray<T>.Empty : value;
+        foreach (var item in normalized)
+        {
+            JsonSerializer.Serialize(writer, item, options);
+        }
+
+        writer.WriteEndArray();
+    }
+}