fix: extract tool arguments from ToolExecutionStartEvent in sidecar

The CopilotTurnExecutionState was ignoring ToolExecutionStartData.Arguments
when creating tool-calling activity events, despite the Copilot SDK providing
them. This caused the activity panel to show 'Viewed a file' / 'Used rg'
with no contextual details (file paths, search patterns, etc.).

The fix adds NormalizeRawToolArguments to WorkflowRequestInfoInterpreter for
converting the raw object? payload (typically JsonElement) into the normalized
dictionary, then passes ToolExecutionStartData.Arguments through
CreateToolCallingActivity.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

sidecar/src/Aryx.AgentHost/Services/CopilotTurnExecutionState.cs

@@ -98,7 +98,8 @@ internal sealed class CopilotTurnExecutionState
                 string toolName = toolExecutionStart.Data.ToolName.Trim();
                 ToolNamesByCallId[toolCallId] = toolName;
                 ActiveAgent = agent;
-                AgentActivityEventDto? toolActivity = CreateToolCallingActivity(agent, toolName, toolCallId);
+                AgentActivityEventDto? toolActivity = CreateToolCallingActivity(
+                    agent, toolName, toolCallId, toolExecutionStart.Data.Arguments);
                 if (toolActivity is not null)
                 {
                     _pendingEvents.Enqueue(toolActivity);
@@ -295,7 +296,8 @@ internal sealed class CopilotTurnExecutionState
     private AgentActivityEventDto? CreateToolCallingActivity(
         AgentIdentity agent,
         string toolName,
-        string toolCallId)
+        string toolCallId,
+        object? rawArguments = null)
     {
         if (toolName.StartsWith("handoff_to_", StringComparison.Ordinal))
         {
@@ -312,6 +314,7 @@ internal sealed class CopilotTurnExecutionState
             AgentName = agent.AgentName,
             ToolName = toolName,
             ToolCallId = toolCallId,
+            ToolArguments = WorkflowRequestInfoInterpreter.NormalizeRawToolArguments(rawArguments),
         };
     }
 

sidecar/src/Aryx.AgentHost/Services/WorkflowRequestInfoInterpreter.cs

@@ -205,6 +205,26 @@ internal static class WorkflowRequestInfoInterpreter
         return false;
     }
 
+    public static IReadOnlyDictionary<string, object?>? NormalizeRawToolArguments(object? rawArguments)
+    {
+        return rawArguments switch
+        {
+            null => null,
+            JsonElement { ValueKind: JsonValueKind.Object } element => NormalizeToolArgumentObject(element),
+            IEnumerable<KeyValuePair<string, object?>> dictionary => NormalizeToolArguments(dictionary),
+            _ => NormalizeRawToolArgumentsViaJson(rawArguments),
+        };
+    }
+
+    private static IReadOnlyDictionary<string, object?>? NormalizeRawToolArgumentsViaJson(object value)
+    {
+        string json = JsonSerializer.Serialize(value, value.GetType(), JsonOptions);
+        using JsonDocument document = JsonDocument.Parse(json);
+        return document.RootElement.ValueKind == JsonValueKind.Object
+            ? NormalizeToolArgumentObject(document.RootElement)
+            : null;
+    }
+
     private static IReadOnlyDictionary<string, object?>? NormalizeToolArguments(
         IEnumerable<KeyValuePair<string, object?>>? arguments)
     {

sidecar/tests/Aryx.AgentHost.Tests/CopilotTurnExecutionStateTests.cs

@@ -68,16 +68,33 @@ public sealed class CopilotTurnExecutionStateTests
         state.ObserveSessionEvent(
             command.Workflow.GetAgentNodes()[0],
             SessionEvent.FromJson(
-                """{"type":"tool.execution_start","data":{"toolCallId":"tool-call-1","toolName":"view"},"id":"33333333-3333-3333-3333-333333333333","timestamp":"2026-03-27T00:00:00Z"}"""));
+                """{"type":"tool.execution_start","data":{"toolCallId":"tool-call-1","toolName":"view","arguments":{"path":"/src/main.ts","view_range":[10,20]}},"id":"33333333-3333-3333-3333-333333333333","timestamp":"2026-03-27T00:00:00Z"}"""));
 
         AgentActivityEventDto toolActivity = Assert.Single(state.DrainPendingEvents().OfType<AgentActivityEventDto>());
         Assert.Equal("tool-calling", toolActivity.ActivityType);
         Assert.Equal("view", toolActivity.ToolName);
         Assert.Equal("tool-call-1", toolActivity.ToolCallId);
+        Assert.NotNull(toolActivity.ToolArguments);
+        Assert.Equal("/src/main.ts", toolActivity.ToolArguments["path"]);
         Assert.True(state.ToolNamesByCallId.TryGetValue("tool-call-1", out string? toolName));
         Assert.Equal("view", toolName);
     }
 
+    [Fact]
+    public void ObserveSessionEvent_ToolExecutionStart_WithoutArguments_SetsToolArgumentsToNull()
+    {
+        RunTurnCommandDto command = CreateCommand();
+        CopilotTurnExecutionState state = new(command);
+
+        state.ObserveSessionEvent(
+            command.Workflow.GetAgentNodes()[0],
+            SessionEvent.FromJson(
+                """{"type":"tool.execution_start","data":{"toolCallId":"tool-call-1","toolName":"view"},"id":"33333333-3333-3333-3333-333333333333","timestamp":"2026-03-27T00:00:00Z"}"""));
+
+        AgentActivityEventDto toolActivity = Assert.Single(state.DrainPendingEvents().OfType<AgentActivityEventDto>());
+        Assert.Null(toolActivity.ToolArguments);
+    }
+
     [Fact]
     public void ObserveSessionEvent_ToolExecutionStart_DoesNotQueueToolActivityForHandoffTools()
     {

sidecar/tests/Aryx.AgentHost.Tests/WorkflowRequestInfoInterpreterTests.cs

@@ -1,6 +1,7 @@
 using System.Collections;
 using System.Collections.Concurrent;
 using System.Runtime.CompilerServices;
+using System.Text.Json;
 using Aryx.AgentHost.Contracts;
 using Aryx.AgentHost.Services;
 using Microsoft.Agents.AI;
@@ -255,6 +256,35 @@ public sealed class WorkflowRequestInfoInterpreterTests
         Assert.False(requiresBoundary);
     }
 
+    [Fact]
+    public void NormalizeRawToolArguments_JsonElement_ExtractsArguments()
+    {
+        using JsonDocument doc = JsonDocument.Parse("""{"path":"/src/main.ts","view_range":[10,20]}""");
+        JsonElement element = doc.RootElement.Clone();
+
+        IReadOnlyDictionary<string, object?>? result = WorkflowRequestInfoInterpreter.NormalizeRawToolArguments(element);
+
+        Assert.NotNull(result);
+        Assert.Equal("/src/main.ts", result["path"]);
+        IReadOnlyList<object?> viewRange = Assert.IsAssignableFrom<IReadOnlyList<object?>>(result["view_range"]);
+        Assert.Equal(2, viewRange.Count);
+    }
+
+    [Fact]
+    public void NormalizeRawToolArguments_Null_ReturnsNull()
+    {
+        Assert.Null(WorkflowRequestInfoInterpreter.NormalizeRawToolArguments(null));
+    }
+
+    [Fact]
+    public void NormalizeRawToolArguments_EmptyObject_ReturnsNull()
+    {
+        using JsonDocument doc = JsonDocument.Parse("{}");
+        JsonElement element = doc.RootElement.Clone();
+
+        Assert.Null(WorkflowRequestInfoInterpreter.NormalizeRawToolArguments(element));
+    }
+
     private static RunTurnCommandDto CreateSingleAgentCommand()
         => CreateCommand("single", [CreateAgent("agent-1", "Primary")]);