Add system_message field to ResumeSessionConfig in all SDKs

Co-authored-by: patniko <26906478+patniko@users.noreply.github.com>

Author: Copilot

dotnet/src/Types.cs

@@ -771,6 +771,12 @@ public class SessionConfig
 public class ResumeSessionConfig
 {
     public ICollection<AIFunction>? Tools { get; set; }
+
+    /// <summary>
+    /// System message configuration for the session.
+    /// </summary>
+    public SystemMessageConfig? SystemMessage { get; set; }
+
     public ProviderConfig? Provider { get; set; }
 
     /// <summary>

go/types.go

@@ -401,6 +401,8 @@ type ToolResult struct {
 type ResumeSessionConfig struct {
 	// Tools exposes caller-implemented tools to the CLI
 	Tools []Tool
+	// SystemMessage configures the system message for the session
+	SystemMessage *SystemMessageConfig
 	// Provider configures a custom model provider
 	Provider *ProviderConfig
 	// ReasoningEffort level for models that support it.

nodejs/src/types.ts

@@ -731,6 +731,7 @@ export interface SessionConfig {
 export type ResumeSessionConfig = Pick<
     SessionConfig,
     | "tools"
+    | "systemMessage"
     | "provider"
     | "streaming"
     | "reasoningEffort"

python/copilot/types.py

@@ -493,6 +493,7 @@ class ResumeSessionConfig(TypedDict, total=False):
     """Configuration for resuming a session"""
 
     tools: list[Tool]
+    system_message: SystemMessageConfig  # System message configuration
     provider: ProviderConfig
     # Reasoning effort level for models that support it.
     reasoning_effort: ReasoningEffort