Add history.clearContext and Tool.isTerminal across all SDKs

docs/features/README.md

@@ -20,6 +20,7 @@ These guides cover the capabilities you can add to your Copilot SDK application.
 | [Streaming Events](./streaming-events.md) | Subscribe to real-time session events (40+ event types) |
 | [Usage and Billing](./usage-and-billing.md) | Read token counts, context-window utilization, AI credit cost, and account quota |
 | [Steering & Queueing](./steering-and-queueing.md) | Control message delivery—immediate steering vs. sequential queueing |
+| [Context Clearing](./context-management.md) | Replace conversation context safely with terminal tools |
 | [Session Persistence](./session-persistence.md) | Resume sessions across restarts, manage session storage |
 | [Remote Sessions](./remote-sessions.md) | Share locally hosted sessions to GitHub web and mobile via Mission Control |
 | [Cloud Sessions](./cloud-sessions.md) | Run sessions on GitHub-hosted compute through Mission Control |

docs/features/context-management.md

@@ -0,0 +1,57 @@
+# Context clearing and terminal tools
+
+Use `session.history.clearContext` when a host needs to replace the current conversation context without replacing the session. Typical uses include handoffs and host-managed context lifecycle policies.
+
+Context clearing is different from creating a new session: it preserves the session identity, system and developer messages, configuration, and event log while removing the model-facing conversation.
+
+> [!IMPORTANT]
+> `clearContext` is a tool-handler primitive. The runtime rejects calls made without a tool call in flight, calls with an empty seed prompt, and calls on remote sessions.
+
+## Define a context-clearing tool
+
+A successful context-clearing tool should be terminal. Otherwise, the agent loop may make another model call against the newly cleared window before starting the seeded turn.
+
+```typescript
+import { approveAll, CopilotClient, defineTool } from "@github/copilot-sdk";
+import type { CopilotSession } from "@github/copilot-sdk";
+import { z } from "zod";
+
+const client = new CopilotClient();
+let session: CopilotSession;
+
+session = await client.createSession({
+  onPermissionRequest: approveAll,
+  tools: [
+    defineTool("clear_context", {
+      description: "Clear the conversation and start a fresh context window",
+      parameters: z.object({ prompt: z.string() }),
+      isTerminal: true,
+      defer: "never",
+      handler: async ({ prompt }) => {
+        const { messagesCleared } =
+          await session.rpc.history.clearContext({ prompt });
+        return `Cleared ${messagesCleared} messages.`;
+      },
+    }),
+  ],
+});
+```
+
+The required `prompt` becomes the first user message in the fresh context. A successful clear emits `session.context_cleared` with the number of removed messages and the initial message.
+
+## Terminal-tool behavior
+
+`isTerminal` ends the current agent turn only when the tool succeeds. A failure, denial, rejection, timeout, or input-validation error remains visible to the model so it can recover or retry.
+
+The option follows each language's naming conventions:
+
+| SDK | Tool option |
+|---|---|
+| Node.js | `isTerminal` |
+| Python | `is_terminal` |
+| Go | `IsTerminal` |
+| .NET | `CopilotToolOptions.IsTerminal` |
+| Java | `ToolDefinition.isTerminal(true)` or `@CopilotTool(isTerminal = true)` |
+| Rust | `with_is_terminal(true)` |
+
+Use terminality only for tools whose successful completion should end the turn. Ordinary tools should leave it unset.

docs/troubleshooting/compatibility.md

@@ -89,6 +89,7 @@ The Copilot SDK communicates with the CLI via JSON-RPC protocol. Features must b
 | Agent management | `session.rpc.agent.*` | List, select, deselect, get current agent |
 | Fleet mode | `session.rpc.fleet.start()` | Parallel sub-agent execution; see [Fleet mode](../features/fleet-mode.md) |
 | Manual compaction | `session.rpc.history.compact()` | Trigger compaction on demand |
+| Context clearing | `session.rpc.history.clearContext()` | Replace conversation context from a terminal tool |
 | History truncation | `session.rpc.history.truncate()` | Remove events from a point onward |
 | Session forking | `server.rpc.sessions.fork()` | Fork a session at a point in history |
 

dotnet/src/Client.cs

@@ -2788,19 +2788,22 @@ 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/ClientSessionLifetimeTests.cs

@@ -287,6 +287,39 @@ public async Task SessionRequests_Serialize_AdditionalDirectories()
             value => Assert.Equal("/repo/resumed", value.GetString()));
     }
 
+    [Fact]
+    public async Task SessionRequests_Serialize_Terminal_Tools()
+    {
+        await using var server = await FakeCopilotServer.StartAsync();
+        await using var client = new CopilotClient(new CopilotClientOptions { Connection = RuntimeConnection.ForUri(server.Url) });
+        var terminalTool = CopilotTool.DefineTool(
+            (Func<string>)(() => "done"),
+            new CopilotToolOptions { IsTerminal = true });
+        var plainTool = CopilotTool.DefineTool((Func<string>)(() => "continue"));
+
+        await using var created = await client.CreateSessionAsync(new SessionConfig
+        {
+            Tools = [terminalTool, plainTool],
+            OnPermissionRequest = PermissionHandler.ApproveAll
+        });
+
+        var createRequest = Assert.Single(server.Requests, request => request.Method == "session.create");
+        var createTools = createRequest.Params.GetProperty("tools");
+        Assert.True(createTools[0].GetProperty("isTerminal").GetBoolean());
+        Assert.False(createTools[1].TryGetProperty("isTerminal", out _));
+
+        server.ClearRequests();
+
+        await using var resumed = await client.ResumeSessionAsync("resume-with-terminal-tool", new ResumeSessionConfig
+        {
+            Tools = [terminalTool],
+            OnPermissionRequest = PermissionHandler.ApproveAll
+        });
+
+        var resumeRequest = Assert.Single(server.Requests, request => request.Method == "session.resume");
+        Assert.True(resumeRequest.Params.GetProperty("tools")[0].GetProperty("isTerminal").GetBoolean());
+    }
+
     [Fact]
     public async Task CreateSessionAsync_Registers_McpAuth_Interest_Only_When_Handler_Configured()
     {

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

@@ -3478,3 +3478,40 @@ 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

@@ -1472,6 +1472,11 @@ 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"`

java/src/main/java/com/github/copilot/rpc/ToolDefinition.java

@@ -78,6 +78,11 @@
  * @param metadata
  *            opaque, host-defined metadata; keys are namespaced and not part of
  *            the stable public API; {@code null} when unset
+ * @param isTerminal
+ *            when {@code true}, a successful call to this tool ends the agent
+ *            turn: the runtime's tool phase halts instead of feeding the result
+ *            back to the model for another round; {@code null} or {@code false}
+ *            leaves the turn running
  * @see SessionConfig#setTools(java.util.List)
  * @see ToolHandler
  * @since 1.0.0
@@ -87,13 +92,13 @@ public record ToolDefinition(@JsonProperty("name") String name, @JsonProperty("d
         @JsonProperty("parameters") Object parameters, @JsonIgnore ToolHandler handler,
         @JsonProperty("overridesBuiltInTool") Boolean overridesBuiltInTool,
         @JsonProperty("skipPermission") Boolean skipPermission, @JsonProperty("defer") ToolDefer defer,
-        @JsonProperty("metadata") Map<String, Object> metadata) {
+        @JsonProperty("metadata") Map<String, Object> metadata, @JsonProperty("isTerminal") Boolean isTerminal) {
 
     /**
-     * Creates a tool definition without a {@code metadata} bag.
+     * Creates a tool definition without a {@code metadata} bag or terminality hint.
      * <p>
      * Convenience overload equivalent to the canonical constructor with
-     * {@code metadata} set to {@code null}.
+     * {@code metadata} and {@code isTerminal} set to {@code null}.
      *
      * @param name
      *            the unique name of the tool
@@ -114,7 +119,37 @@ public record ToolDefinition(@JsonProperty("name") String name, @JsonProperty("d
      */
     public ToolDefinition(String name, String description, Object parameters, ToolHandler handler,
             Boolean overridesBuiltInTool, Boolean skipPermission, ToolDefer defer) {
-        this(name, description, parameters, handler, overridesBuiltInTool, skipPermission, defer, null);
+        this(name, description, parameters, handler, overridesBuiltInTool, skipPermission, defer, null, null);
+    }
+
+    /**
+     * Creates a tool definition without a terminality hint.
+     * <p>
+     * Convenience overload equivalent to the canonical constructor with
+     * {@code isTerminal} set to {@code null}.
+     *
+     * @param name
+     *            the unique name of the tool
+     * @param description
+     *            a description of what the tool does
+     * @param parameters
+     *            the JSON Schema for the tool's parameters
+     * @param handler
+     *            the handler function to execute when invoked
+     * @param overridesBuiltInTool
+     *            whether this tool overrides a built-in tool; {@code null} for the
+     *            default
+     * @param skipPermission
+     *            whether the tool may run without a permission check; {@code null}
+     *            for the default
+     * @param defer
+     *            the deferral mode; {@code null} lets the runtime decide
+     * @param metadata
+     *            the opaque, host-defined metadata; {@code null} when unset
+     */
+    public ToolDefinition(String name, String description, Object parameters, ToolHandler handler,
+            Boolean overridesBuiltInTool, Boolean skipPermission, ToolDefer defer, Map<String, Object> metadata) {
+        this(name, description, parameters, handler, overridesBuiltInTool, skipPermission, defer, metadata, null);
     }
 
     /**
@@ -304,7 +339,8 @@ public static List<ToolDefinition> fromClass(Class<?> clazz) {
      */
     @CopilotExperimental
     public ToolDefinition overridesBuiltInTool(boolean value) {
-        return new ToolDefinition(name, description, parameters, handler, value, skipPermission, defer, metadata);
+        return new ToolDefinition(name, description, parameters, handler, value, skipPermission, defer, metadata,
+                isTerminal);
     }
 
     /**
@@ -318,7 +354,8 @@ public ToolDefinition overridesBuiltInTool(boolean value) {
      */
     @CopilotExperimental
     public ToolDefinition skipPermission(boolean value) {
-        return new ToolDefinition(name, description, parameters, handler, overridesBuiltInTool, value, defer, metadata);
+        return new ToolDefinition(name, description, parameters, handler, overridesBuiltInTool, value, defer, metadata,
+                isTerminal);
     }
 
     /**
@@ -333,7 +370,7 @@ public ToolDefinition skipPermission(boolean value) {
     @CopilotExperimental
     public ToolDefinition defer(ToolDefer value) {
         return new ToolDefinition(name, description, parameters, handler, overridesBuiltInTool, skipPermission, value,
-                metadata);
+                metadata, isTerminal);
     }
 
     /**
@@ -348,7 +385,22 @@ public ToolDefinition defer(ToolDefer value) {
     @CopilotExperimental
     public ToolDefinition metadata(Map<String, Object> value) {
         return new ToolDefinition(name, description, parameters, handler, overridesBuiltInTool, skipPermission, defer,
-                value);
+                value, isTerminal);
+    }
+
+    /**
+     * Returns a copy with the {@code isTerminal} flag set.
+     *
+     * @param value
+     *            {@code true} to end the agent turn after a successful call to this
+     *            tool
+     * @return a new {@code ToolDefinition} with the flag applied
+     * @since 1.0.11
+     */
+    @CopilotExperimental
+    public ToolDefinition isTerminal(boolean value) {
+        return new ToolDefinition(name, description, parameters, handler, overridesBuiltInTool, skipPermission, defer,
+                metadata, value);
     }
 
     // ------------------------------------------------------------------

java/src/main/java/com/github/copilot/tool/CopilotTool.java

@@ -48,6 +48,9 @@
     /** Whether to skip permission checks. */
     boolean skipPermission() default false;
 
+    /** Whether a successful call to this tool ends the agent turn. */
+    boolean isTerminal() default false;
+
     /** Defer configuration for this tool. */
     ToolDefer defer() default ToolDefer.NONE;