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Expose exp_assignments injection on session create/resume across all SDKs #1750

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ff50921
Add exp_assignments injection to session create/resume config
ellismg Jun 22, 2026
a5828ed
Expose exp_assignments injection across Node, Python, Go, .NET, Java …
ellismg Jun 22, 2026
ba36305
Merge remote-tracking branch 'origin/main' into ellismg-expose-exp-as…
ellismg Jun 23, 2026
e3cbdaa
Fix .NET clone dropping ExpAssignments + add clone regression coverage
ellismg Jun 23, 2026
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12 changes: 8 additions & 4 deletions dotnet/src/Client.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1012,7 +1012,8 @@ public async Task<CopilotSession> CreateSessionAsync(SessionConfig config, Cance
ExtensionInfo: config.ExtensionInfo,
Providers: config.Providers,
Models: config.Models,
ToolFilterPrecedence: toolFilter.ToolFilterPrecedence);
ToolFilterPrecedence: toolFilter.ToolFilterPrecedence,
ExpAssignments: config.ExpAssignments);

var rpcTimestamp = Stopwatch.GetTimestamp();

Expand Down Expand Up @@ -1213,7 +1214,8 @@ public async Task<CopilotSession> ResumeSessionAsync(string sessionId, ResumeSes
OpenCanvases: config.OpenCanvases,
Providers: config.Providers,
Models: config.Models,
ToolFilterPrecedence: toolFilter.ToolFilterPrecedence);
ToolFilterPrecedence: toolFilter.ToolFilterPrecedence,
ExpAssignments: config.ExpAssignments);

var rpcTimestamp = Stopwatch.GetTimestamp();
var response = await InvokeRpcAsync<ResumeSessionResponse>(
Expand Down Expand Up @@ -2411,7 +2413,8 @@ internal record CreateSessionRequest(
ExtensionInfo? ExtensionInfo = null,
IList<NamedProviderConfig>? Providers = null,
IList<ProviderModelConfig>? Models = null,
OptionsUpdateToolFilterPrecedence? ToolFilterPrecedence = null);
OptionsUpdateToolFilterPrecedence? ToolFilterPrecedence = null,
[property: JsonPropertyName("expAssignments")] JsonElement? ExpAssignments = null);
#pragma warning restore GHCP001

internal record ToolDefinition(
Expand Down Expand Up @@ -2506,7 +2509,8 @@ internal record ResumeSessionRequest(
IList<OpenCanvasInstance>? OpenCanvases = null,
IList<NamedProviderConfig>? Providers = null,
IList<ProviderModelConfig>? Models = null,
OptionsUpdateToolFilterPrecedence? ToolFilterPrecedence = null);
OptionsUpdateToolFilterPrecedence? ToolFilterPrecedence = null,
[property: JsonPropertyName("expAssignments")] JsonElement? ExpAssignments = null);
#pragma warning restore GHCP001

internal record ResumeSessionResponse(
Expand Down
18 changes: 18 additions & 0 deletions dotnet/src/Types.cs
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Expand Up @@ -2667,6 +2667,7 @@ protected SessionConfigBase(SessionConfigBase? other)
CreateSessionFsProvider = other.CreateSessionFsProvider;
GitHubToken = other.GitHubToken;
RemoteSession = other.RemoteSession;
ExpAssignments = other.ExpAssignments;
#pragma warning disable GHCP001
Canvases = other.Canvases is not null ? [.. other.Canvases] : null;
RequestCanvasRenderer = other.RequestCanvasRenderer;
Expand Down Expand Up @@ -3043,6 +3044,23 @@ protected SessionConfigBase(SessionConfigBase? other)
/// </summary>
public RemoteSessionMode? RemoteSession { get; set; }

/// <summary>
/// ExP assignment ("flight") data injected by a trusted integrator, in the
/// same JSON shape the Copilot CLI fetches from the experimentation service
/// (<c>CopilotExpAssignmentResponse</c>). When provided, the runtime feeds it
/// into the same feature-flag path as CLI-fetched assignments and stamps it
/// onto telemetry and the CAPI request header. When unset, the session does
/// not block on ExP. Intended for out-of-process integrators that fetch ExP
/// data themselves; malformed payloads are dropped by the runtime (fail-open).
/// Serialized on the wire as <c>expAssignments</c>.
/// </summary>
/// <remarks>
/// This is an internal/trusted-integrator option and is hidden from editor
/// completion. It is not part of the broadly advertised public surface.
/// </remarks>
[EditorBrowsable(EditorBrowsableState.Never)]
public JsonElement? ExpAssignments { get; set; }
Comment on lines +3061 to +3062

@ellismg ellismg Jun 23, 2026

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Good catch — fixed in e3cbdaa. SessionConfigBase's copy constructor now copies ExpAssignments (right after RemoteSession), so both SessionConfig.Clone() and ResumeSessionConfig.Clone() preserve it.

I audited every config copy/clone/normalize path across all 6 SDKs, since the original tests only checked serialization from a freshly-built config and never exercised a copy path:

  • .NET — had the gap (this fix). Grepped the other copy sites (SessionConfig/ResumeSessionConfig derived copy ctors only forward their own fields and chain : base(other)), so the base ctor was the one place to fix.
  • Java — already safe: SessionConfig.clone() and ResumeSessionConfig.clone() both assign expAssignments.
  • Rust — already safe: both configs #[derive(Clone)] with no hand-written Clone impl, so all fields (incl. exp_assignments) are copied.
  • Node — already safe: createSession/resumeSession normalize via { ...configDefaultsForMode(), ...config }, and object spread carries all own properties including expAssignments.
  • Go — already safe: create/resume assign req.ExpAssignments = config.ExpAssignments directly off the config pointer (no struct-copy in between).
  • Python — already safe: exp_assignments is an explicit kwarg mapped straight into payload["expAssignments"]; no intermediate dict that could drop it.

Regression coverage added for the three SDKs with explicit Clone()/clone() methods — each sets expAssignments, clones, and asserts it survives and is forwarded on the resulting create/resume request:

  • .NET: SessionConfigClone_PreservesExpAssignments, ResumeSessionConfigClone_PreservesExpAssignments — these fail against the pre-fix copy constructor (verified by reverting the one-line fix: both red, then green again).
  • Java: testClonePreservesAndForwardsExpAssignments.
  • Rust: session_config_clone_preserves_exp_assignments, resume_session_config_clone_preserves_exp_assignments.
  • Node's existing forward test already drives the spread-normalization copy path via createSession.

Re: the two CodeQL findings on this file — they flagged my new tests calling the deprecated single-arg buildCreateRequest(SessionConfig). Switched both to the current buildCreateRequest(SessionConfig, String) overload, so no new CodeQL debt. (The deprecated single-arg form is a pre-existing pattern used ~30 times elsewhere in this test file; I only touched the lines I added.)

Full 6-language validation green post-fix: Rust fmt/clippy + exp tests, Node typecheck + tests, Python tests + ruff, Go gofmt/build/tests, .NET 42 serialization tests, Java 83 SessionRequestBuilderTest + spotless.


#pragma warning disable GHCP001
/// <summary>
/// Canvas declarations advertised by this connection. The runtime forwards
Expand Down
91 changes: 91 additions & 0 deletions dotnet/test/Unit/SerializationTests.cs
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Expand Up @@ -442,6 +442,97 @@ public void SessionRequests_OmitMemory_WhenUnset()
Assert.False(resumeDocument.RootElement.TryGetProperty("memory", out _));
}

[Fact]
public void SessionRequests_CanSerializeExpAssignments_WithSdkOptions()
{
var options = GetSerializerOptions();

using var createAssignments = JsonDocument.Parse("""{"Configs":[{"Id":"exp-create"}]}""");
var createRequestType = GetNestedType(typeof(CopilotClient), "CreateSessionRequest");
var createRequest = CreateInternalRequest(
createRequestType,
("SessionId", "session-id"),
("ExpAssignments", createAssignments.RootElement.Clone()));

var createJson = JsonSerializer.Serialize(createRequest, createRequestType, options);
using var createDocument = JsonDocument.Parse(createJson);
var createRoot = createDocument.RootElement;
Assert.Equal("exp-create", createRoot.GetProperty("expAssignments").GetProperty("Configs")[0].GetProperty("Id").GetString());

using var resumeAssignments = JsonDocument.Parse("""{"Configs":[{"Id":"exp-resume"}]}""");
var resumeRequestType = GetNestedType(typeof(CopilotClient), "ResumeSessionRequest");
var resumeRequest = CreateInternalRequest(
resumeRequestType,
("SessionId", "session-id"),
("ExpAssignments", resumeAssignments.RootElement.Clone()));

var resumeJson = JsonSerializer.Serialize(resumeRequest, resumeRequestType, options);
using var resumeDocument = JsonDocument.Parse(resumeJson);
var resumeRoot = resumeDocument.RootElement;
Assert.Equal("exp-resume", resumeRoot.GetProperty("expAssignments").GetProperty("Configs")[0].GetProperty("Id").GetString());
}

[Fact]
public void SessionRequests_OmitExpAssignments_WhenUnset()
{
var options = GetSerializerOptions();

var createRequestType = GetNestedType(typeof(CopilotClient), "CreateSessionRequest");
var createRequest = CreateInternalRequest(
createRequestType,
("SessionId", "session-id"));

var createJson = JsonSerializer.Serialize(createRequest, createRequestType, options);
using var createDocument = JsonDocument.Parse(createJson);
Assert.False(createDocument.RootElement.TryGetProperty("expAssignments", out _));

var resumeRequestType = GetNestedType(typeof(CopilotClient), "ResumeSessionRequest");
var resumeRequest = CreateInternalRequest(
resumeRequestType,
("SessionId", "session-id"));

var resumeJson = JsonSerializer.Serialize(resumeRequest, resumeRequestType, options);
using var resumeDocument = JsonDocument.Parse(resumeJson);
Assert.False(resumeDocument.RootElement.TryGetProperty("expAssignments", out _));
}

[Fact]
public void SessionConfigClone_PreservesExpAssignments()
{
using var assignments = JsonDocument.Parse("""{"Configs":[{"Id":"exp-create"}]}""");

var config = new SessionConfig
{
SessionId = "session-id",
ExpAssignments = assignments.RootElement.Clone(),
};

var clone = config.Clone();

Assert.True(clone.ExpAssignments.HasValue);
Assert.Equal(
"exp-create",
clone.ExpAssignments!.Value.GetProperty("Configs")[0].GetProperty("Id").GetString());
}

[Fact]
public void ResumeSessionConfigClone_PreservesExpAssignments()
{
using var assignments = JsonDocument.Parse("""{"Configs":[{"Id":"exp-resume"}]}""");

var config = new ResumeSessionConfig
{
ExpAssignments = assignments.RootElement.Clone(),
};

var clone = config.Clone();

Assert.True(clone.ExpAssignments.HasValue);
Assert.Equal(
"exp-resume",
clone.ExpAssignments!.Value.GetProperty("Configs")[0].GetProperty("Id").GetString());
}

[Fact]
public void CreateSessionRequest_CanSerializeEnableSessionTelemetry_WithSdkOptions()
{
Expand Down
2 changes: 2 additions & 0 deletions go/client.go
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Expand Up @@ -711,6 +711,7 @@ func (c *Client) CreateSession(ctx context.Context, config *SessionConfig) (*Ses
req.RequestCanvasRenderer = config.RequestCanvasRenderer
req.RequestExtensions = config.RequestExtensions
req.ExtensionSDKPath = config.ExtensionSDKPath
req.ExpAssignments = config.ExpAssignments

if len(config.Commands) > 0 {
cmds := make([]wireCommand, 0, len(config.Commands))
Expand Down Expand Up @@ -1051,6 +1052,7 @@ func (c *Client) ResumeSessionWithOptions(ctx context.Context, sessionID string,
req.RequestCanvasRenderer = config.RequestCanvasRenderer
req.RequestExtensions = config.RequestExtensions
req.ExtensionSDKPath = config.ExtensionSDKPath
req.ExpAssignments = config.ExpAssignments
if config.OnPermissionRequest != nil {
req.RequestPermission = Bool(true)
}
Expand Down
82 changes: 82 additions & 0 deletions go/client_test.go
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Expand Up @@ -2220,3 +2220,85 @@ func TestStartCLIServer_StderrFieldSet(t *testing.T) {
t.Error("expected Stderr to be *truncbuffer.TruncBuffer after assignment")
}
}

func TestCreateSessionRequest_ExpAssignments(t *testing.T) {
assignments := map[string]any{
"Parameters": map[string]any{"copilot_exp_flag": "treatment"},
"AssignmentContext": "ctx-123",
}

t.Run("includes expAssignments in JSON when set", func(t *testing.T) {
req := createSessionRequest{ExpAssignments: assignments}
data, err := json.Marshal(req)
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)
}
got, ok := m["expAssignments"].(map[string]any)
if !ok {
t.Fatalf("Expected expAssignments to be an object, got %v", m["expAssignments"])
}
if got["AssignmentContext"] != "ctx-123" {
t.Errorf("Expected AssignmentContext 'ctx-123', got %v", got["AssignmentContext"])
}
})

t.Run("omits expAssignments from JSON when nil", func(t *testing.T) {
req := createSessionRequest{}
data, err := json.Marshal(req)
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["expAssignments"]; ok {
t.Error("Expected expAssignments to be omitted when nil")
}
})
}

func TestResumeSessionRequest_ExpAssignments(t *testing.T) {
assignments := map[string]any{
"Parameters": map[string]any{"copilot_exp_flag": "treatment"},
"AssignmentContext": "ctx-456",
}

t.Run("includes expAssignments in JSON when set", func(t *testing.T) {
req := resumeSessionRequest{SessionID: "s1", ExpAssignments: assignments}
data, err := json.Marshal(req)
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)
}
got, ok := m["expAssignments"].(map[string]any)
if !ok {
t.Fatalf("Expected expAssignments to be an object, got %v", m["expAssignments"])
}
if got["AssignmentContext"] != "ctx-456" {
t.Errorf("Expected AssignmentContext 'ctx-456', got %v", got["AssignmentContext"])
}
})

t.Run("omits expAssignments from JSON when nil", func(t *testing.T) {
req := resumeSessionRequest{SessionID: "s1"}
data, err := json.Marshal(req)
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["expAssignments"]; ok {
t.Error("Expected expAssignments to be omitted when nil")
}
})
}
22 changes: 22 additions & 0 deletions go/types.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1134,6 +1134,18 @@ type SessionConfig struct {
CanvasHandler CanvasHandler `json:"-"`
// ExtensionInfo identifies the stable extension providing this session's canvases.
ExtensionInfo *ExtensionInfo
// ExpAssignments injects ExP assignment ("flight") data for this session,
// in the same JSON shape the Copilot CLI fetches from the experimentation
// service (CopilotExpAssignmentResponse). When supplied, the runtime feeds
// it into the same feature-flag path as CLI-fetched assignments and stamps
// it onto telemetry and the CAPI request header. When absent, the session
// does not block on ExP. Malformed payloads are dropped by the runtime
// (fail-open).
//
// Internal: ExpAssignments is part of the SDK's internal API surface,
// intended for trusted out-of-process integrators, and is not intended for
// general external use.
ExpAssignments any
}

// ToolDefer controls whether a tool may be deferred (loaded lazily via tool
Expand Down Expand Up @@ -1529,6 +1541,14 @@ type ResumeSessionConfig struct {
CanvasHandler CanvasHandler `json:"-"`
// ExtensionInfo identifies the stable extension providing this session's canvases.
ExtensionInfo *ExtensionInfo
// ExpAssignments injects ExP assignment ("flight") data on resume. See
// SessionConfig.ExpAssignments. Re-supply on resume so the runtime
// re-applies the assignments after a CLI process restart.
//
// Internal: ExpAssignments is part of the SDK's internal API surface,
// intended for trusted out-of-process integrators, and is not intended for
// general external use.
ExpAssignments any
}
type ProviderConfig struct {
// Type is the provider type: "openai", "azure", or "anthropic". Defaults to "openai".
Expand Down Expand Up @@ -1879,6 +1899,7 @@ type createSessionRequest struct {
RequestExtensions *bool `json:"requestExtensions,omitempty"`
ExtensionSDKPath *string `json:"extensionSdkPath,omitempty"`
ExtensionInfo *ExtensionInfo `json:"extensionInfo,omitempty"`
ExpAssignments any `json:"expAssignments,omitempty"`
Traceparent string `json:"traceparent,omitempty"`
Tracestate string `json:"tracestate,omitempty"`
}
Expand Down Expand Up @@ -1963,6 +1984,7 @@ type resumeSessionRequest struct {
RequestExtensions *bool `json:"requestExtensions,omitempty"`
ExtensionSDKPath *string `json:"extensionSdkPath,omitempty"`
ExtensionInfo *ExtensionInfo `json:"extensionInfo,omitempty"`
ExpAssignments any `json:"expAssignments,omitempty"`
Traceparent string `json:"traceparent,omitempty"`
Tracestate string `json:"tracestate,omitempty"`
}
Expand Down
2 changes: 2 additions & 0 deletions java/src/main/java/com/github/copilot/SessionRequestBuilder.java
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Expand Up @@ -177,6 +177,7 @@ static CreateSessionRequest buildCreateRequest(SessionConfig config, String sess
request.setGitHubToken(config.getGitHubToken());
request.setRemoteSession(config.getRemoteSession());
request.setCloud(config.getCloud());
request.setExpAssignments(config.getExpAssignments());

return request;
}
Expand Down Expand Up @@ -294,6 +295,7 @@ static ResumeSessionRequest buildResumeRequest(String sessionId, ResumeSessionCo
}
request.setGitHubToken(config.getGitHubToken());
request.setRemoteSession(config.getRemoteSession());
request.setExpAssignments(config.getExpAssignments());

return request;
}
Expand Down
16 changes: 16 additions & 0 deletions java/src/main/java/com/github/copilot/rpc/CreateSessionRequest.java
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Expand Up @@ -10,6 +10,7 @@

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.JsonNode;

import com.github.copilot.CopilotExperimental;

Expand Down Expand Up @@ -195,6 +196,9 @@ public final class CreateSessionRequest {
@JsonProperty("cloud")
private CloudSessionOptions cloud;

@JsonProperty("expAssignments")
private JsonNode expAssignments;

/** Gets the model name. @return the model */
public String getModel() {
return model;
Expand Down Expand Up @@ -884,4 +888,16 @@ public CloudSessionOptions getCloud() {
public void setCloud(CloudSessionOptions cloud) {
this.cloud = cloud;
}

/** Gets the ExP assignment data. @return the ExP assignment data */
public JsonNode getExpAssignments() {
return expAssignments;
}

/**
* Sets the ExP assignment data. @param expAssignments the ExP assignment data
*/
public void setExpAssignments(JsonNode expAssignments) {
this.expAssignments = expAssignments;
}
}
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