Add history.clearContext and Tool.isTerminal across all SDKs

dotnet/src/Client.cs

@@ -2772,19 +2772,22 @@ internal record ToolDefinition(
         bool? OverridesBuiltInTool = null,
         bool? SkipPermission = null,
         CopilotToolDefer? Defer = null,
-        IDictionary<string, JsonNode?>? Metadata = null)
+        IDictionary<string, JsonNode?>? Metadata = null,
+        bool? IsTerminal = null)
     {
         public static ToolDefinition FromAIFunction(AIFunctionDeclaration function)
         {
             var overrides = function.AdditionalProperties.TryGetValue(CopilotTool.OverridesBuiltInToolKey, out var val) && val is true;
             var skipPerm = function.AdditionalProperties.TryGetValue(CopilotTool.SkipPermissionKey, out var skipVal) && skipVal is true;
             var defer = function.AdditionalProperties.TryGetValue(CopilotTool.DeferKey, out var deferVal) && deferVal is CopilotToolDefer d ? d : (CopilotToolDefer?)null;
             var metadata = function.AdditionalProperties.TryGetValue(CopilotTool.MetadataKey, out var metaVal) && metaVal is IDictionary<string, JsonNode?> m ? m : null;
+            var isTerminal = function.AdditionalProperties.TryGetValue(CopilotTool.IsTerminalKey, out var terminalVal) && terminalVal is true;
             return new ToolDefinition(function.Name, function.Description, function.JsonSchema,
                 overrides ? true : null,
                 skipPerm ? true : null,
                 defer,
-                metadata);
+                metadata,
+                isTerminal ? true : null);
         }
     }
 

dotnet/src/CopilotTool.cs

@@ -18,6 +18,9 @@ public static class CopilotTool
     /// <summary>The key used in <see cref="AITool.AdditionalProperties"/> to indicate that a tool can execute without a permission prompt.</summary>
     internal const string SkipPermissionKey = "skip_permission";
 
+    /// <summary>The key used in <see cref="AITool.AdditionalProperties"/> to indicate that a successful call to the tool ends the agent turn.</summary>
+    internal const string IsTerminalKey = "is_terminal";
+
     /// <summary>The key used in <see cref="AITool.AdditionalProperties"/> to carry the tool's <see cref="CopilotToolDefer"/> deferral mode.</summary>
     internal const string DeferKey = "defer";
 
@@ -91,7 +94,7 @@ static void ApplyToolInvocationBinding(AIFunctionFactoryOptions factoryOptions)
 
         static void ApplyToolOptions(AIFunctionFactoryOptions factoryOptions, CopilotToolOptions? toolOptions)
         {
-            if (toolOptions is not null && (toolOptions.OverridesBuiltInTool || toolOptions.SkipPermission || toolOptions.Defer is not null || toolOptions.Metadata is not null))
+            if (toolOptions is not null && (toolOptions.OverridesBuiltInTool || toolOptions.SkipPermission || toolOptions.IsTerminal || toolOptions.Defer is not null || toolOptions.Metadata is not null))
             {
                 Dictionary<string, object?> additionalProperties = new(StringComparer.Ordinal);
                 if (factoryOptions.AdditionalProperties is not null)
@@ -112,6 +115,11 @@ static void ApplyToolOptions(AIFunctionFactoryOptions factoryOptions, CopilotToo
                     additionalProperties[SkipPermissionKey] = true;
                 }
 
+                if (toolOptions.IsTerminal)
+                {
+                    additionalProperties[IsTerminalKey] = true;
+                }
+
                 if (toolOptions.Defer is { } defer)
                 {
                     additionalProperties[DeferKey] = defer;
@@ -152,6 +160,16 @@ public sealed class CopilotToolOptions
     /// </remarks>
     public bool SkipPermission { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether a successful call to this tool ends the agent turn.
+    /// </summary>
+    /// <remarks>
+    /// When true, the runtime's tool phase halts after a successful call instead of feeding the result back to the
+    /// model for another round. A failed call leaves the loop running so the model can read the error and retry.
+    /// The resulting <see cref="AIFunction"/> includes "is_terminal": true in its <see cref="AITool.AdditionalProperties"/>.
+    /// </remarks>
+    public bool IsTerminal { get; set; }
+
     /// <summary>
     /// Gets or sets a value controlling whether this tool may be deferred (loaded lazily via tool search) rather than always pre-loaded.
     /// </summary>

dotnet/test/Unit/CopilotToolTests.cs

@@ -34,6 +34,28 @@ public void DefineTool_Sets_Name_Description_And_Copilot_Metadata()
         Assert.Equal(CopilotToolDefer.Auto, defer);
     }
 
+    [Fact]
+    public void DefineTool_Sets_IsTerminal_Metadata()
+    {
+        var function = CopilotTool.DefineTool(
+            ReturnsOk,
+            new CopilotToolOptions
+            {
+                IsTerminal = true
+            });
+
+        Assert.True(function.AdditionalProperties.TryGetValue("is_terminal", out var isTerminal));
+        Assert.True((bool)isTerminal!);
+    }
+
+    [Fact]
+    public void DefineTool_Omits_IsTerminal_When_Not_Set()
+    {
+        var function = CopilotTool.DefineTool(ReturnsOk);
+
+        Assert.False(function.AdditionalProperties.ContainsKey("is_terminal"));
+    }
+
     [Fact]
     public void DefineTool_Omits_Copilot_Metadata_When_Flags_Are_False()
     {

go/client_test.go

@@ -3305,3 +3305,40 @@ func TestResumeSessionRequest_ExpAssignments(t *testing.T) {
 		}
 	})
 }
+
+func TestIsTerminal(t *testing.T) {
+	t.Run("IsTerminal is serialized in tool definition", func(t *testing.T) {
+		tool := Tool{
+			Name:        "clear_context",
+			Description: "Clear the conversation",
+			IsTerminal:  true,
+			Handler:     func(_ ToolInvocation) (ToolResult, error) { return ToolResult{}, nil },
+		}
+		data, err := json.Marshal(tool)
+		if err != nil {
+			t.Fatalf("Failed to marshal: %v", err)
+		}
+		var m map[string]any
+		if err := json.Unmarshal(data, &m); err != nil {
+			t.Fatalf("Failed to unmarshal: %v", err)
+		}
+		if m["isTerminal"] != true {
+			t.Errorf("Expected isTerminal to be true, got %v", m["isTerminal"])
+		}
+	})
+
+	t.Run("IsTerminal is omitted when false", func(t *testing.T) {
+		tool := Tool{Name: "plain", Description: "A plain tool"}
+		data, err := json.Marshal(tool)
+		if err != nil {
+			t.Fatalf("Failed to marshal: %v", err)
+		}
+		var m map[string]any
+		if err := json.Unmarshal(data, &m); err != nil {
+			t.Fatalf("Failed to unmarshal: %v", err)
+		}
+		if _, ok := m["isTerminal"]; ok {
+			t.Error("Expected isTerminal to be omitted when false")
+		}
+	})
+}

go/types.go

@@ -1452,6 +1452,11 @@ type Tool struct {
 	Parameters           map[string]any `json:"parameters,omitzero"`
 	OverridesBuiltInTool bool           `json:"overridesBuiltInTool,omitempty"`
 	SkipPermission       bool           `json:"skipPermission,omitempty"`
+	// IsTerminal reports that a successful call to this tool ends the agent
+	// turn: the runtime halts instead of feeding the result back to the model
+	// for another round. A failed call leaves the loop running so the model can
+	// read the error and retry.
+	IsTerminal bool `json:"isTerminal,omitempty"`
 	// Defer controls whether the tool may be deferred (loaded lazily via tool
 	// search) rather than always pre-loaded. When empty, the runtime decides.
 	Defer ToolDefer `json:"defer,omitempty"`