fix(mcp): project multi-content AIContent[] tool results for models

src/Netclaw.Actors.Tests/Tools/McpToolResultFormatterTests.cs

@@ -4,6 +4,7 @@
 // </copyright>
 // -----------------------------------------------------------------------
 using System.Text.Json;
+using Microsoft.Extensions.AI;
 using Netclaw.Actors.Tools;
 using Netclaw.Configuration;
 using Netclaw.Tools;
@@ -134,4 +135,48 @@ public void Plain_string_result_is_passed_through()
     [Fact]
     public void Null_result_is_empty()
         => Assert.Equal(string.Empty, McpToolResultFormatter.Format(null, "srv/tool"));
+
+    [Fact]
+    public void Multi_content_AIContent_array_projects_text_and_image_marker()
+    {
+        var chartJson = """{"title":"Example title","series":[]}""";
+        var result = new AIContent[]
+        {
+            new DataContent(new byte[] { 1, 2, 3 }, "image/png"),
+            new TextContent(chartJson),
+        };
+
+        var message = McpToolResultFormatter.Format(result, "srv/chart");
+
+        Assert.Equal($"[image: image/png]\n{chartJson}", message);
+        Assert.DoesNotContain("AIContent", message);
+    }
+
+    [Fact]
+    public void Image_only_AIContent_array_projects_marker_only()
+    {
+        var result = new AIContent[] { new DataContent(Array.Empty<byte>(), "image/jpeg") };
+
+        Assert.Equal("[image: image/jpeg]", McpToolResultFormatter.Format(result, "srv/tool"));
+    }
+
+    [Fact]
+    public void Text_only_AIContent_array_projects_text()
+    {
+        var result = new AIContent[] { new TextContent("hello world") };
+
+        Assert.Equal("hello world", McpToolResultFormatter.Format(result, "srv/tool"));
+    }
+
+    [Fact]
+    public void Single_TextContent_is_passed_through()
+        => Assert.Equal("done", McpToolResultFormatter.Format(new TextContent("done"), "srv/tool"));
+
+    [Fact]
+    public void Non_image_DataContent_projects_attachment_marker()
+    {
+        var result = new AIContent[] { new DataContent(new byte[] { 4, 5 }, "application/pdf") };
+
+        Assert.Equal("[attachment: application/pdf]", McpToolResultFormatter.Format(result, "srv/tool"));
+    }
 }

src/Netclaw.Actors/Tools/McpToolResultFormatter.cs

@@ -4,6 +4,7 @@
 // </copyright>
 // -----------------------------------------------------------------------
 using System.Text.Json;
+using Microsoft.Extensions.AI;
 using Netclaw.Tools;
 
 namespace Netclaw.Actors.Tools;
@@ -57,6 +58,15 @@ public static string Format(object? result, string toolName)
             return string.IsNullOrWhiteSpace(detail) ? element.GetRawText() : detail;
         }
 
+        if (result is AIContent singleContent)
+            return FormatAiContent(singleContent);
+
+        if (result is AIContent[] contentArray)
+            return FormatAiContents(contentArray);
+
+        if (result is IEnumerable<AIContent> contents)
+            return FormatAiContents(contents);
+
         return result?.ToString() ?? string.Empty;
     }
 
@@ -121,4 +131,36 @@ private static string JoinTextContent(JsonElement element)
 
         return string.Join("\n", parts);
     }
+
+    private static string FormatAiContents(IEnumerable<AIContent> contents)
+    {
+        var parts = new List<string>();
+        foreach (var content in contents)
+        {
+            var part = FormatAiContent(content);
+            if (!string.IsNullOrEmpty(part))
+                parts.Add(part);
+        }
+
+        return string.Join("\n", parts);
+    }
+
+    private static string FormatAiContent(AIContent content)
+        => content switch
+        {
+            TextContent text when !string.IsNullOrEmpty(text.Text) => text.Text,
+            DataContent data => FormatDataContentMarker(data),
+            _ => string.Empty,
+        };
+
+    private static string FormatDataContentMarker(DataContent data)
+    {
+        var mediaType = string.IsNullOrWhiteSpace(data.MediaType)
+            ? "application/octet-stream"
+            : data.MediaType;
+
+        return mediaType.StartsWith("image/", StringComparison.OrdinalIgnoreCase)
+            ? $"[image: {mediaType}]"
+            : $"[attachment: {mediaType}]";
+    }
 }