Add copy constructors and Clone methods to the various .NET config option bags (#422)

* Add copy constructors and Clone methods to the various .NET config option bags

Consuming libraries like Agent Framework sometimes have a need to clone the various options bags, e.g. their caller passes in options and that middle library needs to tweak the settings before passing them along (e.g. set Streaming to true or false) but it doesn't want to mutate the caller's object. Without clone methods, such libraries need to manually copy every property, which then means when new properties are added, they get ignored and options are lost.

This PR adds such public Clone methods, and accomodates the non-sealed nature of the types by adding protected copy constructors that the virtual Clone methods use. (If instead we want to seal these types, that'd be viable as well.)

* Address copilot feedback

Author: stephentoub

dotnet/src/Types.cs

@@ -24,6 +24,34 @@ public enum ConnectionState
 
 public class CopilotClientOptions
 {
+    /// <summary>
+    /// Initializes a new instance of the <see cref="CopilotClientOptions"/> class.
+    /// </summary>
+    public CopilotClientOptions() { }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="CopilotClientOptions"/> class
+    /// by copying the properties of the specified instance.
+    /// </summary>
+    protected CopilotClientOptions(CopilotClientOptions? other)
+    {
+        if (other is null) return;
+
+        AutoRestart = other.AutoRestart;
+        AutoStart = other.AutoStart;
+        CliArgs = (string[]?)other.CliArgs?.Clone();
+        CliPath = other.CliPath;
+        CliUrl = other.CliUrl;
+        Cwd = other.Cwd;
+        Environment = other.Environment;
+        GithubToken = other.GithubToken;
+        Logger = other.Logger;
+        LogLevel = other.LogLevel;
+        Port = other.Port;
+        UseLoggedInUser = other.UseLoggedInUser;
+        UseStdio = other.UseStdio;
+    }
+
     /// <summary>
     /// Path to the Copilot CLI executable. If not specified, uses the bundled CLI from the SDK.
     /// </summary>
@@ -53,6 +81,17 @@ public class CopilotClientOptions
     /// Default: true (but defaults to false when GithubToken is provided).
     /// </summary>
     public bool? UseLoggedInUser { get; set; }
+
+    /// <summary>
+    /// Creates a shallow clone of this <see cref="CopilotClientOptions"/> instance.
+    /// </summary>
+    /// <remarks>
+    /// Mutable collection properties are copied into new collection instances so that modifications
+    /// to those collections on the clone do not affect the original.
+    /// Other reference-type properties (for example delegates and the logger) are not
+    /// deep-cloned; the original and the clone will share those objects.
+    /// </remarks>
+    public virtual CopilotClientOptions Clone() => new(this);
 }
 
 public class ToolBinaryResult
@@ -692,6 +731,42 @@ public class InfiniteSessionConfig
 
 public class SessionConfig
 {
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SessionConfig"/> class.
+    /// </summary>
+    public SessionConfig() { }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SessionConfig"/> class
+    /// by copying the properties of the specified instance.
+    /// </summary>
+    protected SessionConfig(SessionConfig? other)
+    {
+        if (other is null) return;
+
+        AvailableTools = other.AvailableTools is not null ? [.. other.AvailableTools] : null;
+        ConfigDir = other.ConfigDir;
+        CustomAgents = other.CustomAgents is not null ? [.. other.CustomAgents] : null;
+        DisabledSkills = other.DisabledSkills is not null ? [.. other.DisabledSkills] : null;
+        ExcludedTools = other.ExcludedTools is not null ? [.. other.ExcludedTools] : null;
+        Hooks = other.Hooks;
+        InfiniteSessions = other.InfiniteSessions;
+        McpServers = other.McpServers is not null
+            ? new Dictionary<string, object>(other.McpServers, other.McpServers.Comparer)
+            : null;
+        Model = other.Model;
+        OnPermissionRequest = other.OnPermissionRequest;
+        OnUserInputRequest = other.OnUserInputRequest;
+        Provider = other.Provider;
+        ReasoningEffort = other.ReasoningEffort;
+        SessionId = other.SessionId;
+        SkillDirectories = other.SkillDirectories is not null ? [.. other.SkillDirectories] : null;
+        Streaming = other.Streaming;
+        SystemMessage = other.SystemMessage;
+        Tools = other.Tools is not null ? [.. other.Tools] : null;
+        WorkingDirectory = other.WorkingDirectory;
+    }
+
     public string? SessionId { get; set; }
     public string? Model { get; set; }
 
@@ -769,10 +844,58 @@ public class SessionConfig
     /// When enabled (default), sessions automatically manage context limits and persist state.
     /// </summary>
     public InfiniteSessionConfig? InfiniteSessions { get; set; }
+
+    /// <summary>
+    /// Creates a shallow clone of this <see cref="SessionConfig"/> instance.
+    /// </summary>
+    /// <remarks>
+    /// Mutable collection properties are copied into new collection instances so that modifications
+    /// to those collections on the clone do not affect the original.
+    /// Other reference-type properties (for example provider configuration, system messages,
+    /// hooks, infinite session configuration, and delegates) are not deep-cloned; the original
+    /// and the clone will share those nested objects, and changes to them may affect both.
+    /// </remarks>
+    public virtual SessionConfig Clone() => new(this);
 }
 
 public class ResumeSessionConfig
 {
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ResumeSessionConfig"/> class.
+    /// </summary>
+    public ResumeSessionConfig() { }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ResumeSessionConfig"/> class
+    /// by copying the properties of the specified instance.
+    /// </summary>
+    protected ResumeSessionConfig(ResumeSessionConfig? other)
+    {
+        if (other is null) return;
+
+        AvailableTools = other.AvailableTools is not null ? [.. other.AvailableTools] : null;
+        ConfigDir = other.ConfigDir;
+        CustomAgents = other.CustomAgents is not null ? [.. other.CustomAgents] : null;
+        DisabledSkills = other.DisabledSkills is not null ? [.. other.DisabledSkills] : null;
+        DisableResume = other.DisableResume;
+        ExcludedTools = other.ExcludedTools is not null ? [.. other.ExcludedTools] : null;
+        Hooks = other.Hooks;
+        InfiniteSessions = other.InfiniteSessions;
+        McpServers = other.McpServers is not null
+            ? new Dictionary<string, object>(other.McpServers, other.McpServers.Comparer)
+            : null;
+        Model = other.Model;
+        OnPermissionRequest = other.OnPermissionRequest;
+        OnUserInputRequest = other.OnUserInputRequest;
+        Provider = other.Provider;
+        ReasoningEffort = other.ReasoningEffort;
+        SkillDirectories = other.SkillDirectories is not null ? [.. other.SkillDirectories] : null;
+        Streaming = other.Streaming;
+        SystemMessage = other.SystemMessage;
+        Tools = other.Tools is not null ? [.. other.Tools] : null;
+        WorkingDirectory = other.WorkingDirectory;
+    }
+
     /// <summary>
     /// Model to use for this session. Can change the model when resuming.
     /// </summary>
@@ -870,13 +993,54 @@ public class ResumeSessionConfig
     /// Infinite session configuration for persistent workspaces and automatic compaction.
     /// </summary>
     public InfiniteSessionConfig? InfiniteSessions { get; set; }
+
+    /// <summary>
+    /// Creates a shallow clone of this <see cref="ResumeSessionConfig"/> instance.
+    /// </summary>
+    /// <remarks>
+    /// Mutable collection properties are copied into new collection instances so that modifications
+    /// to those collections on the clone do not affect the original.
+    /// Other reference-type properties (for example provider configuration, system messages,
+    /// hooks, infinite session configuration, and delegates) are not deep-cloned; the original
+    /// and the clone will share those nested objects, and changes to them may affect both.
+    /// </remarks>
+    public virtual ResumeSessionConfig Clone() => new(this);
 }
 
 public class MessageOptions
 {
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageOptions"/> class.
+    /// </summary>
+    public MessageOptions() { }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageOptions"/> class
+    /// by copying the properties of the specified instance.
+    /// </summary>
+    protected MessageOptions(MessageOptions? other)
+    {
+        if (other is null) return;
+
+        Attachments = other.Attachments is not null ? [.. other.Attachments] : null;
+        Mode = other.Mode;
+        Prompt = other.Prompt;
+    }
+
     public string Prompt { get; set; } = string.Empty;
     public List<UserMessageDataAttachmentsItem>? Attachments { get; set; }
     public string? Mode { get; set; }
+
+    /// <summary>
+    /// Creates a shallow clone of this <see cref="MessageOptions"/> instance.
+    /// </summary>
+    /// <remarks>
+    /// Mutable collection properties are copied into new collection instances so that modifications
+    /// to those collections on the clone do not affect the original.
+    /// Other reference-type properties (for example attachment items) are not deep-cloned;
+    /// the original and the clone will share those nested objects.
+    /// </remarks>
+    public virtual MessageOptions Clone() => new(this);
 }
 
 public delegate void SessionEventHandler(SessionEvent sessionEvent);