Add rewind support across SDKs

Expose file change tracking on create and resume session options in all six SDKs, and add shared replay coverage that verifies conversation-and-file rewind behavior.

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

Copilot-Session: 91a7e2ab-88a5-4365-accf-cbea1e1391e9

Author: stephentoub

dotnet/src/Client.cs

@@ -1141,6 +1141,7 @@ public async Task<CopilotSession> CreateSessionAsync(SessionConfig config, Cance
                 config.ContextTier,
                 config.Tools?.Select(ToolDefinition.FromAIFunction).ToList(),
                 config.EnableCitations,
+                config.EnableFileChangeTracking,
                 wireSystemMessage,
                 toolFilter.AvailableTools,
                 toolFilter.ExcludedTools,
@@ -1360,6 +1361,7 @@ public async Task<CopilotSession> ResumeSessionAsync(string sessionId, ResumeSes
                 config.ContextTier,
                 config.Tools?.Select(ToolDefinition.FromAIFunction).ToList(),
                 config.EnableCitations,
+                config.EnableFileChangeTracking,
                 wireSystemMessage,
                 toolFilter.AvailableTools,
                 toolFilter.ExcludedTools,
@@ -2719,6 +2721,7 @@ internal record CreateSessionRequest(
         ContextTier? ContextTier,
         IList<ToolDefinition>? Tools,
         bool? EnableCitations,
+        bool? EnableFileChangeTracking,
         SystemMessageConfig? SystemMessage,
         IList<string>? AvailableTools,
         IList<string>? ExcludedTools,
@@ -2832,6 +2835,7 @@ internal record ResumeSessionRequest(
         ContextTier? ContextTier,
         IList<ToolDefinition>? Tools,
         bool? EnableCitations,
+        bool? EnableFileChangeTracking,
         SystemMessageConfig? SystemMessage,
         IList<string>? AvailableTools,
         IList<string>? ExcludedTools,

dotnet/src/Types.cs

@@ -3136,6 +3136,7 @@ protected SessionConfigBase(SessionConfigBase? other)
         DisabledSkills = other.DisabledSkills is not null ? [.. other.DisabledSkills] : null;
         DisabledMcpServers = other.DisabledMcpServers is not null ? [.. other.DisabledMcpServers] : null;
         EnableCitations = other.EnableCitations;
+        EnableFileChangeTracking = other.EnableFileChangeTracking;
         EnableConfigDiscovery = other.EnableConfigDiscovery;
         SkipEmbeddingRetrieval = other.SkipEmbeddingRetrieval;
         EmbeddingCacheStorage = other.EmbeddingCacheStorage;
@@ -3263,6 +3264,17 @@ protected SessionConfigBase(SessionConfigBase? other)
     [Experimental(Diagnostics.Experimental)]
     public bool? EnableCitations { get; set; }
 
+    /// <summary>
+    /// Opts in to capturing file changes for session rewind and cumulative
+    /// session diff.
+    /// </summary>
+    /// <remarks>
+    /// On create, capture starts with the first turn. On resume, tracking can be
+    /// enabled only when the session still has a valid baseline; earlier untracked
+    /// changes cannot be reconstructed.
+    /// </remarks>
+    public bool? EnableFileChangeTracking { get; set; }
+
     /// <summary>
     /// Override the default configuration directory location.
     /// When specified, the session will use this directory for storing config and state.

dotnet/test/E2E/RewindE2ETests.cs

@@ -0,0 +1,81 @@
+// Copyright (c) GitHub, Inc.
+// Licensed under the MIT License.
+
+using GitHub.Copilot.Rpc;
+using GitHub.Copilot.Test.Harness;
+
+using Xunit;
+using Xunit.Abstractions;
+
+namespace GitHub.Copilot.Test.E2E;
+
+public class RewindE2ETests(E2ETestFixture fixture, ITestOutputHelper output)
+    : E2ETestBase(fixture, "rewind", output)
+{
+    private const string FileName = "rewind-sdk.txt";
+    private const string FileContent = "SDK rewind content";
+
+    [Fact]
+    public async Task Should_Restore_Tracked_File_And_Conversation()
+    {
+        var filePath = Path.Combine(Ctx.WorkDir, FileName);
+        await using var session = await CreateSessionAsync(new SessionConfig
+        {
+            Model = "claude-sonnet-4.5",
+            EnableFileChangeTracking = true,
+        });
+
+        var response = await session.SendAndWaitAsync(
+            new MessageOptions
+            {
+                Prompt = $"Use the create tool to create {FileName} containing exactly {FileContent}. "
+                    + "After the tool succeeds, reply with exactly SDK_REWIND_DONE.",
+            },
+            TimeSpan.FromSeconds(30));
+
+        Assert.Equal("SDK_REWIND_DONE", response?.Data.Content);
+        Assert.True(File.Exists(filePath));
+        Assert.Equal(FileContent, await File.ReadAllTextAsync(filePath));
+
+        HistoryListRewindPointsResult? rewindPoints = null;
+        await TestHelper.WaitForConditionAsync(
+            async () =>
+            {
+                rewindPoints = await session.Rpc.History.ListRewindPointsAsync();
+                return rewindPoints.UnavailableReason is null;
+            },
+            timeout: TimeSpan.FromSeconds(10),
+            timeoutMessage: "Timed out waiting for rewind points to become available.",
+            pollInterval: TimeSpan.FromMilliseconds(100));
+
+        Assert.NotNull(rewindPoints);
+        Assert.True(rewindPoints.FileChangeTrackingEnabled);
+        var rewindPoint = Assert.Single(rewindPoints.Points);
+        Assert.True(rewindPoint.CanRestoreFiles);
+        Assert.Equal(1, rewindPoint.FileCount);
+
+        var preview = await session.Rpc.History.PreviewRewindAsync(rewindPoint.EventId);
+        Assert.True(preview.Available);
+        var previewFile = Assert.Single(preview.Files);
+        Assert.Equal(
+            Path.GetFullPath(filePath),
+            Path.GetFullPath(previewFile.Path),
+            OperatingSystem.IsWindows() ? StringComparer.OrdinalIgnoreCase : StringComparer.Ordinal);
+
+        var rewind = await session.Rpc.History.RewindAsync(
+            rewindPoint.EventId,
+            HistoryRewindMode.ConversationAndFiles);
+
+        Assert.Equal(HistoryRewindOutcome.Success, rewind.Outcome);
+        Assert.True(rewind.EventsRemoved > 0);
+        var restoredFile = Assert.Single(rewind.RestoredFiles);
+        Assert.Equal(
+            Path.GetFullPath(filePath),
+            Path.GetFullPath(restoredFile),
+            OperatingSystem.IsWindows() ? StringComparer.OrdinalIgnoreCase : StringComparer.Ordinal);
+        Assert.False(File.Exists(filePath));
+
+        var events = await session.GetEventsAsync();
+        Assert.DoesNotContain(events, sessionEvent => sessionEvent.Id.ToString() == rewindPoint.EventId);
+    }
+}

dotnet/test/Unit/CloneTests.cs

@@ -78,6 +78,7 @@ public void SessionConfig_Clone_CopiesAllProperties()
             AdditionalDirectories = ["/shared", "/generated"],
             Streaming = true,
             EnableCitations = true,
+            EnableFileChangeTracking = true,
             EnableSessionTelemetry = false,
             EnableExperimentalMode = true,
             EnableOnDemandInstructionDiscovery = true,
@@ -125,6 +126,7 @@ public void SessionConfig_Clone_CopiesAllProperties()
         Assert.Equal(original.AdditionalDirectories, clone.AdditionalDirectories);
         Assert.Equal(original.Streaming, clone.Streaming);
         Assert.Equal(original.EnableCitations, clone.EnableCitations);
+        Assert.Equal(original.EnableFileChangeTracking, clone.EnableFileChangeTracking);
         Assert.Equal(original.EnableSessionTelemetry, clone.EnableSessionTelemetry);
         Assert.Equal(original.EnableExperimentalMode, clone.EnableExperimentalMode);
         Assert.Equal(original.EnableOnDemandInstructionDiscovery, clone.EnableOnDemandInstructionDiscovery);

dotnet/test/Unit/SerializationTests.cs

@@ -483,13 +483,15 @@ public void SessionRequests_CanSerializeCitationAgentExclusionAndLimits_WithSdkO
             createRequestType,
             ("SessionId", "session-id"),
             ("EnableCitations", true),
+            ("EnableFileChangeTracking", true),
             ("ExcludedBuiltInAgents", excludedAgents),
             ("SessionLimits", new SessionLimitsConfig { MaxAiCredits = 12.5 }));
 
         var createJson = JsonSerializer.Serialize(createRequest, createRequestType, options);
         using var createDocument = JsonDocument.Parse(createJson);
         var createRoot = createDocument.RootElement;
         Assert.True(createRoot.GetProperty("enableCitations").GetBoolean());
+        Assert.True(createRoot.GetProperty("enableFileChangeTracking").GetBoolean());
         Assert.Equal("explore", createRoot.GetProperty("excludedBuiltinAgents")[0].GetString());
         Assert.Equal(12.5, createRoot.GetProperty("sessionLimits").GetProperty("maxAiCredits").GetDouble());
 
@@ -498,13 +500,15 @@ public void SessionRequests_CanSerializeCitationAgentExclusionAndLimits_WithSdkO
             resumeRequestType,
             ("SessionId", "session-id"),
             ("EnableCitations", true),
+            ("EnableFileChangeTracking", true),
             ("ExcludedBuiltInAgents", excludedAgents),
             ("SessionLimits", new SessionLimitsConfig { MaxAiCredits = 7.25 }));
 
         var resumeJson = JsonSerializer.Serialize(resumeRequest, resumeRequestType, options);
         using var resumeDocument = JsonDocument.Parse(resumeJson);
         var resumeRoot = resumeDocument.RootElement;
         Assert.True(resumeRoot.GetProperty("enableCitations").GetBoolean());
+        Assert.True(resumeRoot.GetProperty("enableFileChangeTracking").GetBoolean());
         Assert.Equal("task", resumeRoot.GetProperty("excludedBuiltinAgents")[1].GetString());
         Assert.Equal(7.25, resumeRoot.GetProperty("sessionLimits").GetProperty("maxAiCredits").GetDouble());
     }

go/client.go

@@ -799,6 +799,7 @@ func (c *Client) CreateSession(ctx context.Context, config *SessionConfig) (*Ses
 	req.Models = config.Models
 	req.EnableSessionTelemetry = config.EnableSessionTelemetry
 	req.EnableCitations = config.EnableCitations
+	req.EnableFileChangeTracking = config.EnableFileChangeTracking
 	req.SessionLimits = config.SessionLimits
 	req.IsExperimentalMode = config.EnableExperimentalMode
 	req.SkipCustomInstructions = config.SkipCustomInstructions
@@ -1148,6 +1149,7 @@ func (c *Client) ResumeSessionWithOptions(ctx context.Context, sessionID string,
 	req.ToolFilterPrecedence = precedence
 	req.ExcludedBuiltInAgents = config.ExcludedBuiltInAgents
 	req.EnableCitations = config.EnableCitations
+	req.EnableFileChangeTracking = config.EnableFileChangeTracking
 	req.SessionLimits = config.SessionLimits
 	if config.Streaming != nil {
 		req.Streaming = config.Streaming

go/client_test.go

@@ -398,14 +398,15 @@ func TestClient_ForwardsNewSessionOptionsToSessionRequests(t *testing.T) {
 	})
 
 	_, err := client.CreateSession(t.Context(), &SessionConfig{
-		ExcludedBuiltInAgents: []string{"explore"},
-		EnableCitations:       Bool(true),
-		SessionLimits:         &rpc.SessionLimitsConfig{MaxAiCredits: float64Ptr(30)},
+		ExcludedBuiltInAgents:    []string{"explore"},
+		EnableCitations:          Bool(true),
+		EnableFileChangeTracking: Bool(true),
+		SessionLimits:            &rpc.SessionLimitsConfig{MaxAiCredits: float64Ptr(30)},
 	})
 	if err != nil {
 		t.Fatalf("CreateSession failed: %v", err)
 	}
-	assertNewSessionOptions(t, <-createParams, true, "explore", 30)
+	assertNewSessionOptions(t, <-createParams, true, true, "explore", 30)
 
 	resumeParams := make(chan json.RawMessage, 1)
 	server.SetRequestHandler("session.resume", func(params json.RawMessage) (json.RawMessage, *jsonrpc2.Error) {
@@ -414,14 +415,15 @@ func TestClient_ForwardsNewSessionOptionsToSessionRequests(t *testing.T) {
 	})
 
 	_, err = client.ResumeSessionWithOptions(t.Context(), "resumed-options", &ResumeSessionConfig{
-		ExcludedBuiltInAgents: []string{"task"},
-		EnableCitations:       Bool(false),
-		SessionLimits:         &rpc.SessionLimitsConfig{MaxAiCredits: float64Ptr(15)},
+		ExcludedBuiltInAgents:    []string{"task"},
+		EnableCitations:          Bool(false),
+		EnableFileChangeTracking: Bool(false),
+		SessionLimits:            &rpc.SessionLimitsConfig{MaxAiCredits: float64Ptr(15)},
 	})
 	if err != nil {
 		t.Fatalf("ResumeSessionWithOptions failed: %v", err)
 	}
-	assertNewSessionOptions(t, <-resumeParams, false, "task", 15)
+	assertNewSessionOptions(t, <-resumeParams, false, false, "task", 15)
 }
 
 func assertCapiEnableWebSocketResponses(t *testing.T, params json.RawMessage) {
@@ -445,6 +447,7 @@ func assertNewSessionOptions(
 	t *testing.T,
 	params json.RawMessage,
 	expectedCitations bool,
+	expectedFileChangeTracking bool,
 	expectedAgent string,
 	expectedCredits float64,
 ) {
@@ -457,6 +460,9 @@ func assertNewSessionOptions(
 	if decoded["enableCitations"] != expectedCitations {
 		t.Fatalf("expected enableCitations=%v, got %v", expectedCitations, decoded["enableCitations"])
 	}
+	if decoded["enableFileChangeTracking"] != expectedFileChangeTracking {
+		t.Fatalf("expected enableFileChangeTracking=%v, got %v", expectedFileChangeTracking, decoded["enableFileChangeTracking"])
+	}
 	agents, ok := decoded["excludedBuiltinAgents"].([]any)
 	if !ok || len(agents) != 1 || agents[0] != expectedAgent {
 		t.Fatalf("expected excludedBuiltinAgents=[%q], got %#v", expectedAgent, decoded["excludedBuiltinAgents"])