@@ -13,7 +13,7 @@ public final class SignalWithStartWorkflowRequest {
    */
   private final java.util.List<Object> args;
   /**
-   * Unique identifier for the workflow execution.
+   * Unique identifier for the workflow execution. Must be nonempty.
    */
   private final String id;
   /**
@@ -26,15 +26,16 @@ public final class SignalWithStartWorkflowRequest {
    */
   private final java.util.List<Object> signalArgs;
   /**
-   * Total workflow execution timeout, including retries and continue-as-new.
+   * Total workflow execution timeout, including retries and continue-as-new. Defaults
+   * to unlimited.
    */
   private final java.time.Duration executionTimeout;
   /**
-   * Timeout of a single workflow run.
+   * Timeout of a single workflow run. Defaults to the workflow execution timeout.
    */
   private final java.time.Duration runTimeout;
   /**
-   * Timeout of a single workflow task.
+   * Timeout of a single workflow task. Defaults to 10 seconds.
    */
   private final java.time.Duration taskTimeout;
   /**
@@ -45,7 +46,7 @@ public final class SignalWithStartWorkflowRequest {
   /**
    * Behavior when a workflow is currently running with the same ID. Set to use-existing
    * for idempotent deduplication on workflow ID. Cannot be set if id-reuse-policy is
-   * terminate-if-running.
+   * terminate-if-running. Defaults to use-existing.
    */
   private final io.temporal.api.enums.v1.WorkflowIdConflictPolicy idConflictPolicy;
   /**
@@ -78,8 +79,17 @@ public final class SignalWithStartWorkflowRequest {
    * cron-schedule.
    */
   private final java.time.Duration startDelay;
+  /**
+   * Static metadata for the workflow execution.
+   */
   private final io.temporal.workflow.UserMetadata userMetadata;
+  /**
+   * Namespace of the workflow execution.
+   */
   private final String namespace;
+  /**
+   * Headers for the request.
+   */
   private final java.util.Map<String, io.temporal.api.common.v1.Payload> headers;
   @com.fasterxml.jackson.annotation.JsonCreator
   public SignalWithStartWorkflowRequest(@com.fasterxml.jackson.annotation.JsonProperty("workflow") String workflow, @com.fasterxml.jackson.annotation.JsonProperty("args") java.util.List<Object> args, @com.fasterxml.jackson.annotation.JsonProperty("id") String id, @com.fasterxml.jackson.annotation.JsonProperty("taskQueue") String taskQueue, @com.fasterxml.jackson.annotation.JsonProperty("signal") String signal, @com.fasterxml.jackson.annotation.JsonProperty("signalArgs") java.util.List<Object> signalArgs, @com.fasterxml.jackson.annotation.JsonProperty("executionTimeout") java.time.Duration executionTimeout, @com.fasterxml.jackson.annotation.JsonProperty("runTimeout") java.time.Duration runTimeout, @com.fasterxml.jackson.annotation.JsonProperty("taskTimeout") java.time.Duration taskTimeout, @com.fasterxml.jackson.annotation.JsonProperty("idReusePolicy") io.temporal.api.enums.v1.WorkflowIdReusePolicy idReusePolicy, @com.fasterxml.jackson.annotation.JsonProperty("idConflictPolicy") io.temporal.api.enums.v1.WorkflowIdConflictPolicy idConflictPolicy, @com.fasterxml.jackson.annotation.JsonProperty("retryPolicy") io.temporal.common.RetryOptions retryPolicy, @com.fasterxml.jackson.annotation.JsonProperty("cronSchedule") String cronSchedule, @com.fasterxml.jackson.annotation.JsonProperty("memo") java.util.Map<String, Object> memo, @com.fasterxml.jackson.annotation.JsonProperty("searchAttributes") io.temporal.common.SearchAttributes searchAttributes, @com.fasterxml.jackson.annotation.JsonProperty("priority") io.temporal.common.Priority priority, @com.fasterxml.jackson.annotation.JsonProperty("versioningOverride") io.temporal.common.VersioningOverride versioningOverride, @com.fasterxml.jackson.annotation.JsonProperty("startDelay") java.time.Duration startDelay, @com.fasterxml.jackson.annotation.JsonProperty("userMetadata") io.temporal.workflow.UserMetadata userMetadata, @com.fasterxml.jackson.annotation.JsonProperty("namespace") String namespace, @com.fasterxml.jackson.annotation.JsonProperty("headers") java.util.Map<String, io.temporal.api.common.v1.Payload> headers) {
 
@@ -1,21 +1,27 @@
 // Generated by nexgen v0.2.9. DO NOT EDIT!
 package io.temporal.workflow;
 
+/**
+ * Result of signaling a workflow and starting it if needed.
+ */
 @io.temporal.common.converter.TransferTypeConvertible(SignalWithStartWorkflowResponse.Converter.class)
 @SuppressWarnings({"unchecked", "rawtypes"})
 public final class SignalWithStartWorkflowResponse {
+  /**
+   * Run ID of the started workflow.
+   */
   private final String runId;
+  /**
+   * Whether the workflow was started.
+   */
   private final Boolean started;
-  private final String firstExecutionRunId;
   @com.fasterxml.jackson.annotation.JsonCreator
-  public SignalWithStartWorkflowResponse(@com.fasterxml.jackson.annotation.JsonProperty("runId") String runId, @com.fasterxml.jackson.annotation.JsonProperty("started") Boolean started, @com.fasterxml.jackson.annotation.JsonProperty("firstExecutionRunId") String firstExecutionRunId) {
+  public SignalWithStartWorkflowResponse(@com.fasterxml.jackson.annotation.JsonProperty("runId") String runId, @com.fasterxml.jackson.annotation.JsonProperty("started") Boolean started) {
     this.runId = runId;
     this.started = started;
-    this.firstExecutionRunId = firstExecutionRunId;
   }
   public String getRunId() { return runId; }
   public Boolean getStarted() { return started; }
-  public String getFirstExecutionRunId() { return firstExecutionRunId; }
   public Builder toBuilder() { return newBuilder(this); }
   public static  Builder newBuilder(SignalWithStartWorkflowResponse value) { return new Builder(value); }
   public static  Builder newBuilder() { return new Builder(); }
@@ -25,28 +31,23 @@ private Builder(SignalWithStartWorkflowResponse value) {
       if (value == null) return;
       this.runId = value.runId;
       this.started = value.started;
-      this.firstExecutionRunId = value.firstExecutionRunId;
     }
     private String runId = null;
     public Builder setRunId(String value) { this.runId = value; return this; }
     private Boolean started = null;
     public Builder setStarted(Boolean value) { this.started = value; return this; }
-    private String firstExecutionRunId = "";
-    public Builder setFirstExecutionRunId(String value) { this.firstExecutionRunId = value; return this; }
-    public SignalWithStartWorkflowResponse build() { return new SignalWithStartWorkflowResponse(runId, started, firstExecutionRunId); }
+    public SignalWithStartWorkflowResponse build() { return new SignalWithStartWorkflowResponse(runId, started); }
   }
   public io.temporal.api.workflowservice.v1.SignalWithStartWorkflowExecutionResponse toProto(io.temporal.common.converter.DataConverter converter) {
     io.temporal.api.workflowservice.v1.SignalWithStartWorkflowExecutionResponse.Builder proto = io.temporal.api.workflowservice.v1.SignalWithStartWorkflowExecutionResponse.newBuilder();
     if (this.runId != null) io.temporal.workflow.NexgenRuntime.set(proto, "run_id", (this.runId));
     if (this.started != null) io.temporal.workflow.NexgenRuntime.set(proto, "started", (this.started));
-    if (this.firstExecutionRunId != null) io.temporal.workflow.NexgenRuntime.set(proto, "first_execution_run_id", (this.firstExecutionRunId));
     return proto.build();
   }
   public static  SignalWithStartWorkflowResponse fromProto(io.temporal.api.workflowservice.v1.SignalWithStartWorkflowExecutionResponse proto, io.temporal.common.converter.DataConverter converter, java.lang.reflect.Type modelType) {
     Builder builder = SignalWithStartWorkflowResponse.newBuilder();
     if (true) builder.setRunId((String) io.temporal.workflow.NexgenRuntime.get(proto, "run_id"));
     if (true) builder.setStarted((Boolean) io.temporal.workflow.NexgenRuntime.get(proto, "started"));
-    if (true) builder.setFirstExecutionRunId((String) io.temporal.workflow.NexgenRuntime.get(proto, "first_execution_run_id"));
     return builder.build();
   }
   public static final class Converter implements io.temporal.common.converter.TransferTypeConverter<SignalWithStartWorkflowResponse> {
 
@@ -1,6 +1,9 @@
 // Generated by nexgen v0.2.9. DO NOT EDIT!
 package io.temporal.workflow;
 
+/**
+ * Static metadata for a workflow execution.
+ */
 @io.temporal.common.converter.TransferTypeConvertible(UserMetadata.Converter.class)
 @SuppressWarnings({"unchecked", "rawtypes"})
 public final class UserMetadata {
 
@@ -1,8 +1,11 @@
 # System Nexus bindings
 
-The WIT definitions here describe the workflow-facing Java models for the
-vendored workflow service. They retain the upstream wire schema and add Java
-native type and serialization context annotations. Protobuf descriptors from
+The WIT definitions here are a temporary copy of the shared multi-language
+definitions in nex-gen's `advanced/samples/inputs/workflow-service.wit` and
+`deps/nexus-temporal-types/model.wit`. Keep the copies identical; Java directives
+belong in the shared source alongside the other languages. The SDK will
+eventually consume these definitions from the API repo instead. Protobuf
+descriptors from
 `temporal-serviceclient:generateProto` validate the mappings during generation.
 
 Regenerate with nex-gen 0.2.9 built with its `advanced` feature:
 
@@ -9,26 +9,48 @@ interface model {
   ///   java="Object"
   ///   python="typing.Any"
   ///   typescript="common.Payload"
+  ///   go="any"
   ///   dotnet="object?"
+  ///   dotnet-from="ProtoExtensions.FromPayload"
   ///   dotnet-to="ProtoExtensions.ToPayload"
   ///   typescript-import="@temporalio/common"
   type payload = placeholder;
 
   /// @nexus.proto "temporal.api.common.v1.Payloads"
   ///   typescript-import="@temporalio/proto"
-  /// @nexus.type dotnet="IReadOnlyCollection<object?>" dotnet-to="ProtoExtensions.ToPayloads"
+  /// @nexus.type
   ///   java="java.util.List<Object>"
+  ///   go="[]any"
+  ///   dotnet="IReadOnlyCollection<object?>"
+  ///   dotnet-from="ProtoExtensions.FromPayloads"
+  ///   dotnet-to="ProtoExtensions.ToPayloads"
   type payloads = list<payload>;
 
+  /// Temporal failure represented by the target SDK's native exception/error type.
+  /// The SDK failure converter owns the recursive cause and failure-info structure.
+  /// @nexus.proto "temporal.api.failure.v1.Failure" typescript-import="@temporalio/proto"
+  /// @nexus.type
+  ///   java="RuntimeException"
+  ///   java-from="failureFromProto"
+  ///   java-to="failureToProto"
+  ///   python="BaseException"
+  ///   typescript="Error"
+  ///   go="error"
+  ///   dotnet="System.Exception"
+  ///   dotnet-from="ProtoExtensions.FromFailureProto"
+  ///   dotnet-to="ProtoExtensions.ToFailureProto"
+  type failure = placeholder;
+
   /// Callable result annotation for workflow functions.
   /// @nexus.type
   ///   python="collections.abc.Awaitable[WorkflowResult]"
   ///   typescript="Promise<any>"
+  ///   go="any"
   ///   dotnet="System.Threading.Tasks.Task<object?>"
   type workflow-result = placeholder;
 
   /// Receiver/context argument for workflow callable method forms.
-  /// @nexus.type python="typing.Any" typescript="any" dotnet="object"
+  /// @nexus.type python="typing.Any" typescript="any" go="go.temporal.io/sdk/workflow:workflow.Context" dotnet="object"
   type callable-prefix = placeholder;
 
   /// @nexus.function-args
@@ -38,7 +60,7 @@ interface model {
   workflow-call: async func(callable-prefix: callable-prefix, args: payloads) -> workflow-result;
 
   /// Callable result annotation for signal functions.
-  /// @nexus.type python="None | collections.abc.Awaitable[None]" typescript="void" dotnet="void"
+  /// @nexus.type python="None | collections.abc.Awaitable[None]" typescript="void" go="any" dotnet="void"
   type signal-result = placeholder;
 
   /// @nexus.function-args
@@ -54,7 +76,9 @@ interface model {
   ///   java-to="workflowTypeToProto"
   ///   python="str"
   ///   typescript="string"
+  ///   go="string"
   ///   dotnet="string"
+  ///   dotnet-from="ProtoExtensions.FromWorkflowTypeProto"
   ///   dotnet-to="ProtoExtensions.ToWorkflowTypeProto"
   type workflow-type = placeholder;
 
@@ -64,6 +88,7 @@ interface model {
   ///   args-field="input"
   ///   result-type-parameter="WorkflowResult"
   ///   alternate-type="workflow-type"
+  ///   go-name-extractor="WorkflowFunctionName"
   ///   dotnet-name-extractor="TemporalFunctionNames.WorkflowName"
   ///   dotnet-call-extractor="TemporalFunctionNames.ExtractCall"
   /// @nexus.add-rpc-compatible-with "workflow-type"
@@ -73,13 +98,15 @@ interface model {
   ///   signature="signal-call"
   ///   args-field="signal-input"
   ///   alternate-type="string"
+  ///   go-value-type="string"
+  ///   go-args-type="any"
   ///   python-converter="signal_function_to_proto"
   ///   typescript-name-extractor="signalFunctionName"
   ///   dotnet-name-extractor="TemporalFunctionNames.SignalName"
   ///   dotnet-call-extractor="TemporalFunctionNames.ExtractCall"
-  ///   typescript-value-type="workflow.SignalDefinition<any[]>"
-  ///   typescript-args-type="Value extends workflow.SignalDefinition<infer Args, any> ? Args : never"
-  ///   typescript-import="@temporalio/workflow"
+  ///   typescript-value-type="common.SignalDefinition<any[]>"
+  ///   typescript-args-type="Value extends common.SignalDefinition<infer Args extends any[], any> ? Args : never"
+  ///   typescript-import="@temporalio/common"
   /// @nexus.add-rpc-compatible-with "string"
   type signal-function = placeholder;
 
@@ -90,7 +117,9 @@ interface model {
   ///   java-to="retryPolicyToProto"
   ///   python="temporalio.common.RetryPolicy"
   ///   typescript="common.RetryPolicy"
+  ///   go="go.temporal.io/sdk/temporal.RetryPolicy"
   ///   dotnet="Temporalio.Common.RetryPolicy"
+  ///   dotnet-from="ProtoExtensions.FromRetryPolicyProto"
   ///   typescript-import="@temporalio/common"
   type retry-policy = placeholder;
 
@@ -101,22 +130,36 @@ interface model {
   ///   java-to="taskQueueToProto"
   ///   python="str"
   ///   typescript="string"
+  ///   go="string"
   ///   dotnet="string"
+  ///   dotnet-from="ProtoExtensions.FromTaskQueueProto"
   ///   dotnet-to="ProtoExtensions.ToTaskQueueProto"
   type task-queue = placeholder;
 
   /// @nexus.proto "temporal.api.common.v1.Memo" typescript-import="@temporalio/proto"
-  /// @nexus.type python="collections.abc.Mapping[str, typing.Any]" typescript="Record<string, unknown>" dotnet="IReadOnlyDictionary<string, object?>"
+  /// @nexus.type
   ///   java="java.util.Map<String, Object>"
   ///   java-from="memoFromProto"
   ///   java-to="memoToProto"
+  ///   python="collections.abc.Mapping[str, typing.Any]"
+  ///   typescript="Record<string, unknown>"
+  ///   go="map[string]any"
+  ///   dotnet="IReadOnlyDictionary<string, object?>"
+  ///   dotnet-from="ProtoExtensions.FromMemoProto"
   type memo = placeholder;
 
-  /// @nexus.proto "temporal.api.common.v1.Header"
+  /// @nexus.proto "temporal.api.common.v1.Header" typescript-import="@temporalio/proto"
   /// @nexus.type
   ///   java="java.util.Map<String, io.temporal.api.common.v1.Payload>"
   ///   java-from="headerFromProto"
   ///   java-to="headerToProto"
+  ///   python="collections.abc.Mapping[str, typing.Any]"
+  ///   typescript="common.Headers"
+  ///   go="map[string]any"
+  ///   dotnet="IReadOnlyDictionary<string, object?>"
+  ///   dotnet-from="ProtoExtensions.FromHeaderProto"
+  ///   dotnet-to="ProtoExtensions.ToHeaderProto"
+  ///   typescript-import="@temporalio/common"
   type header = placeholder;
 
   /// @nexus.proto "temporal.api.common.v1.SearchAttributes" typescript-import="@temporalio/proto"
@@ -126,7 +169,9 @@ interface model {
   ///   java-to="searchAttributesToProto"
   ///   python="temporalio.common.TypedSearchAttributes"
   ///   typescript="common.TypedSearchAttributes"
+  ///   go="go.temporal.io/sdk/temporal.SearchAttributes"
   ///   dotnet="Temporalio.Common.SearchAttributeCollection"
+  ///   dotnet-from="ProtoExtensions.FromSearchAttributesProto"
   ///   typescript-import="@temporalio/common"
   type search-attributes = placeholder;
 
@@ -137,7 +182,9 @@ interface model {
   ///   java-to="priorityToProto"
   ///   python="temporalio.common.Priority"
   ///   typescript="common.Priority"
+  ///   go="go.temporal.io/sdk/temporal.Priority"
   ///   dotnet="Temporalio.Common.Priority"
+  ///   dotnet-from="ProtoExtensions.FromPriorityProto"
   ///   typescript-import="@temporalio/common"
   type priority = placeholder;
 
@@ -148,7 +195,9 @@ interface model {
   ///   java-to="versioningOverrideToProto"
   ///   python="temporalio.common.VersioningOverride"
   ///   typescript="common.VersioningOverride"
+  ///   go="go.temporal.io/sdk/client.VersioningOverride"
   ///   dotnet="Temporalio.Common.VersioningOverride"
+  ///   dotnet-from="ProtoExtensions.FromVersioningOverrideProto"
   ///   typescript-import="@temporalio/common"
   type versioning-override = placeholder;
 
@@ -159,7 +208,9 @@ interface model {
   ///   java-to="durationToProto"
   ///   python="datetime.timedelta"
   ///   typescript="common.Duration"
+  ///   go="time.Duration"
   ///   dotnet="System.TimeSpan"
+  ///   dotnet-from="ProtoExtensions.FromDurationProto"
   ///   typescript-import="@temporalio/common"
   type duration = placeholder;
 
@@ -168,6 +219,7 @@ interface model {
   ///   java="io.temporal.api.enums.v1.WorkflowIdReusePolicy"
   ///   python="temporalio.common.WorkflowIDReusePolicy"
   ///   typescript="common.WorkflowIdReusePolicy"
+  ///   go="go.temporal.io/api/enums/v1:enums.WorkflowIdReusePolicy"
   ///   dotnet="Temporalio.Api.Enums.V1.WorkflowIdReusePolicy"
   ///   typescript-import="@temporalio/common"
   type workflow-id-reuse-policy = placeholder;
@@ -177,20 +229,23 @@ interface model {
   ///   java="io.temporal.api.enums.v1.WorkflowIdConflictPolicy"
   ///   python="temporalio.common.WorkflowIDConflictPolicy"
   ///   typescript="common.WorkflowIdConflictPolicy"
+  ///   go="go.temporal.io/api/enums/v1:enums.WorkflowIdConflictPolicy"
   ///   dotnet="Temporalio.Api.Enums.V1.WorkflowIdConflictPolicy"
   ///   typescript-import="@temporalio/common"
   type workflow-id-conflict-policy = placeholder;
 
+  /// @nexus.doc "Static metadata for a workflow execution."
   /// @nexus.proto "temporal.api.sdk.v1.UserMetadata" typescript-import="@temporalio/proto"
   /// @nexus.flatten-in-api
+  /// @nexus.experimental
   record user-metadata {
     /// @nexus.doc "Single-line fixed summary for the workflow execution that may appear in UI and CLI. This can be in single-line Temporal Markdown format."
     /// @nexus.proto-field "summary"
-    /// @nexus.flattened-type python="str" typescript="string" dotnet="string"
+    /// @nexus.flattened-type python="str" typescript="string" dotnet="string" go="string"
     static-summary: option<payload>,
     /// @nexus.doc "General fixed details for the workflow execution that may appear in UI and CLI. This can be in Temporal Markdown format and can span multiple lines. This value is fixed on the workflow execution and cannot be updated."
     /// @nexus.proto-field "details"
-    /// @nexus.flattened-type python="str" typescript="string" dotnet="string"
+    /// @nexus.flattened-type python="str" typescript="string" dotnet="string" go="string"
     static-details: option<payload>,
   }
 }