Preserve structured JsonElement tool arguments in GitHub Copilot agent events (#5)

* Implement raw JsonElement argument handling

Co-authored-by: kzu <169707+kzu@users.noreply.github.com>
Agent-Logs-Url: https://github.com/kzu/agent-framework/sessions/ca9509f7-6318-4f1a-8ba2-17e4207bc7c4

* Fix test validation and preserve structured JSON args

Co-authored-by: kzu <169707+kzu@users.noreply.github.com>
Agent-Logs-Url: https://github.com/kzu/agent-framework/sessions/ca9509f7-6318-4f1a-8ba2-17e4207bc7c4

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: kzu <169707+kzu@users.noreply.github.com>

Author: Copilot

dotnet/src/Microsoft.Agents.AI.GitHub.Copilot/GitHubCopilotAgent.cs

@@ -500,6 +500,9 @@ internal AgentResponseUpdate ConvertToolCompleteToAgentResponseUpdate(ToolExecut
                 JsonValueKind.Number => property.Value.TryGetInt64(out long l)
                     ? (object?)l
                     : property.Value.GetDouble(),
+                JsonValueKind.Object => property.Value.Clone(),
+                JsonValueKind.Array => property.Value.Clone(),
+                JsonValueKind.Undefined => null,
                 _ => property.Value.GetRawText()
             };
         }

dotnet/tests/Microsoft.Agents.AI.GitHub.Copilot.UnitTests/GitHubCopilotAgentTests.cs

@@ -350,7 +350,8 @@ public void ConvertToolStartToAgentResponseUpdate_WithAllJsonValueKinds_Converts
                     nullVal = (string?)null,
                     intVal = 100,
                     floatVal = 3.14,
-                    objVal = new { nested = "value" }
+                    objVal = new { nested = "value" },
+                    arrVal = new List<int> { 1, 2, 3 }
                 })
             }
         };
@@ -367,8 +368,12 @@ public void ConvertToolStartToAgentResponseUpdate_WithAllJsonValueKinds_Converts
         Assert.Null(content.Arguments["nullVal"]);
         Assert.Equal(100L, content.Arguments["intVal"]);
         Assert.Equal(3.14, (double)content.Arguments["floatVal"]!, 2);
-        // Non-primitive values fall back to raw JSON text
-        Assert.IsType<string>(content.Arguments["objVal"]);
+        JsonElement objValElement = Assert.IsType<JsonElement>(content.Arguments["objVal"]);
+        Assert.Equal(JsonValueKind.Object, objValElement.ValueKind);
+        Assert.Equal("value", objValElement.GetProperty("nested").GetString());
+        JsonElement arrValElement = Assert.IsType<JsonElement>(content.Arguments["arrVal"]);
+        Assert.Equal(JsonValueKind.Array, arrValElement.ValueKind);
+        Assert.Equal(3, arrValElement.GetArrayLength());
     }
 
     [Fact]