Add per-answer thinking disclosure

app/MindWork AI Studio/Provider/OpenAI/ThinkingContent.cs

@@ -0,0 +1,46 @@
+using System.Text.Json;
+
+namespace AIStudio.Provider.OpenAI;
+
+/// <summary>
+/// Reads human-readable thinking from OpenAI-compatible response fields.
+/// </summary>
+internal static class ThinkingContent
+{
+    public static string Get(string? reasoningContent, string? reasoning, IEnumerable<JsonElement>? reasoningDetails)
+    {
+        if (!string.IsNullOrWhiteSpace(reasoningContent))
+            return reasoningContent;
+
+        if (!string.IsNullOrWhiteSpace(reasoning))
+            return reasoning;
+
+        if (reasoningDetails is null)
+            return string.Empty;
+
+        return string.Concat(reasoningDetails.Select(GetVisibleDetailText));
+    }
+
+    private static string GetVisibleDetailText(JsonElement detail)
+    {
+        if (detail.ValueKind is not JsonValueKind.Object ||
+            !detail.TryGetProperty("type", out var typeProperty) ||
+            typeProperty.ValueKind is not JsonValueKind.String)
+            return string.Empty;
+
+        return typeProperty.GetString() switch
+        {
+            "reasoning.text" => ReadString(detail, "text"),
+            "reasoning.summary" => ReadString(detail, "summary"),
+            _ => string.Empty,
+        };
+    }
+
+    private static string ReadString(JsonElement item, string propertyName)
+    {
+        if (!item.TryGetProperty(propertyName, out var property) || property.ValueKind is not JsonValueKind.String)
+            return string.Empty;
+
+        return property.GetString() ?? string.Empty;
+    }
+}