Expose enableConfigDiscovery in all SDK languages

Add enableConfigDiscovery option to session config types in Node.js,
Python, Go, and .NET SDKs. When set to true, the runtime automatically
discovers MCP server configurations (.mcp.json, .vscode/mcp.json) and
skill directories from the working directory, merging them with any
explicitly provided values (explicit takes precedence on name collision).

This surfaces a capability already implemented in copilot-agent-runtime's
resolveDiscoveredConfig() for SDK consumers.

Changes per SDK:
- Node.js: SessionConfig + ResumeSessionConfig pick + client passthrough
- Python: create_session/resume_session params + payload serialization
- Go: config structs + wire request structs + client passthrough
- .NET: config classes + clone constructors + wire records + client passthrough

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

Author: stephentoub

dotnet/src/Client.cs

@@ -502,6 +502,7 @@ public async Task<CopilotSession> CreateSessionAsync(SessionConfig config, Cance
                 config.CustomAgents,
                 config.Agent,
                 config.ConfigDir,
+                config.EnableConfigDiscovery,
                 config.SkillDirectories,
                 config.DisabledSkills,
                 config.InfiniteSessions,
@@ -618,6 +619,7 @@ public async Task<CopilotSession> ResumeSessionAsync(string sessionId, ResumeSes
                 hasHooks ? true : null,
                 config.WorkingDirectory,
                 config.ConfigDir,
+                config.EnableConfigDiscovery,
                 config.DisableResume is true ? true : null,
                 config.Streaming is true ? true : null,
                 config.McpServers,
@@ -1640,6 +1642,7 @@ internal record CreateSessionRequest(
         List<CustomAgentConfig>? CustomAgents,
         string? Agent,
         string? ConfigDir,
+        bool? EnableConfigDiscovery,
         List<string>? SkillDirectories,
         List<string>? DisabledSkills,
         InfiniteSessionConfig? InfiniteSessions,
@@ -1686,6 +1689,7 @@ internal record ResumeSessionRequest(
         bool? Hooks,
         string? WorkingDirectory,
         string? ConfigDir,
+        bool? EnableConfigDiscovery,
         bool? DisableResume,
         bool? Streaming,
         Dictionary<string, object>? McpServers,

dotnet/src/Types.cs

@@ -1603,6 +1603,7 @@ protected SessionConfig(SessionConfig? other)
         CustomAgents = other.CustomAgents is not null ? [.. other.CustomAgents] : null;
         Agent = other.Agent;
         DisabledSkills = other.DisabledSkills is not null ? [.. other.DisabledSkills] : null;
+        EnableConfigDiscovery = other.EnableConfigDiscovery;
         ExcludedTools = other.ExcludedTools is not null ? [.. other.ExcludedTools] : null;
         Hooks = other.Hooks;
         InfiniteSessions = other.InfiniteSessions;
@@ -1660,6 +1661,19 @@ protected SessionConfig(SessionConfig? other)
     /// </summary>
     public string? ConfigDir { get; set; }
 
+    /// <summary>
+    /// When <see langword="true"/>, automatically discovers MCP server configurations
+    /// (e.g. <c>.mcp.json</c>, <c>.vscode/mcp.json</c>) and skill directories from
+    /// the working directory and merges them with any explicitly provided
+    /// <see cref="McpServers"/> and <see cref="SkillDirectories"/>, with explicit
+    /// values taking precedence on name collision.
+    /// <para>
+    /// Custom instruction files (<c>.github/copilot-instructions.md</c>, <c>AGENTS.md</c>, etc.)
+    /// are always loaded from the working directory regardless of this setting.
+    /// </para>
+    /// </summary>
+    public bool? EnableConfigDiscovery { get; set; }
+
     /// <summary>
     /// Custom tool functions available to the language model during the session.
     /// </summary>
@@ -1817,6 +1831,7 @@ protected ResumeSessionConfig(ResumeSessionConfig? other)
         Agent = other.Agent;
         DisabledSkills = other.DisabledSkills is not null ? [.. other.DisabledSkills] : null;
         DisableResume = other.DisableResume;
+        EnableConfigDiscovery = other.EnableConfigDiscovery;
         ExcludedTools = other.ExcludedTools is not null ? [.. other.ExcludedTools] : null;
         Hooks = other.Hooks;
         InfiniteSessions = other.InfiniteSessions;
@@ -1929,6 +1944,19 @@ protected ResumeSessionConfig(ResumeSessionConfig? other)
     /// </summary>
     public string? ConfigDir { get; set; }
 
+    /// <summary>
+    /// When <see langword="true"/>, automatically discovers MCP server configurations
+    /// (e.g. <c>.mcp.json</c>, <c>.vscode/mcp.json</c>) and skill directories from
+    /// the working directory and merges them with any explicitly provided
+    /// <see cref="McpServers"/> and <see cref="SkillDirectories"/>, with explicit
+    /// values taking precedence on name collision.
+    /// <para>
+    /// Custom instruction files (<c>.github/copilot-instructions.md</c>, <c>AGENTS.md</c>, etc.)
+    /// are always loaded from the working directory regardless of this setting.
+    /// </para>
+    /// </summary>
+    public bool? EnableConfigDiscovery { get; set; }
+
     /// <summary>
     /// When true, the session.resume event is not emitted.
     /// Default: false (resume event is emitted).

go/client.go

@@ -578,6 +578,9 @@ func (c *Client) CreateSession(ctx context.Context, config *SessionConfig) (*Ses
 	req.ClientName = config.ClientName
 	req.ReasoningEffort = config.ReasoningEffort
 	req.ConfigDir = config.ConfigDir
+	if config.EnableConfigDiscovery {
+		req.EnableConfigDiscovery = Bool(true)
+	}
 	req.Tools = config.Tools
 	wireSystemMessage, transformCallbacks := extractTransformCallbacks(config.SystemMessage)
 	req.SystemMessage = wireSystemMessage
@@ -754,6 +757,9 @@ func (c *Client) ResumeSessionWithOptions(ctx context.Context, sessionID string,
 	}
 	req.WorkingDirectory = config.WorkingDirectory
 	req.ConfigDir = config.ConfigDir
+	if config.EnableConfigDiscovery {
+		req.EnableConfigDiscovery = Bool(true)
+	}
 	if config.DisableResume {
 		req.DisableResume = Bool(true)
 	}

go/types.go

@@ -465,6 +465,13 @@ type SessionConfig struct {
 	// ConfigDir overrides the default configuration directory location.
 	// When specified, the session will use this directory for storing config and state.
 	ConfigDir string
+	// EnableConfigDiscovery, when true, automatically discovers MCP server configurations
+	// (e.g. .mcp.json, .vscode/mcp.json) and skill directories from the working directory
+	// and merges them with any explicitly provided MCPServers and SkillDirectories, with
+	// explicit values taking precedence on name collision.
+	// Custom instruction files (.github/copilot-instructions.md, AGENTS.md, etc.) are
+	// always loaded from the working directory regardless of this setting.
+	EnableConfigDiscovery bool
 	// Tools exposes caller-implemented tools to the CLI
 	Tools []Tool
 	// SystemMessage configures system message customization
@@ -692,6 +699,13 @@ type ResumeSessionConfig struct {
 	WorkingDirectory string
 	// ConfigDir overrides the default configuration directory location.
 	ConfigDir string
+	// EnableConfigDiscovery, when true, automatically discovers MCP server configurations
+	// (e.g. .mcp.json, .vscode/mcp.json) and skill directories from the working directory
+	// and merges them with any explicitly provided MCPServers and SkillDirectories, with
+	// explicit values taking precedence on name collision.
+	// Custom instruction files (.github/copilot-instructions.md, AGENTS.md, etc.) are
+	// always loaded from the working directory regardless of this setting.
+	EnableConfigDiscovery bool
 	// Streaming enables streaming of assistant message and reasoning chunks.
 	// When true, assistant.message_delta and assistant.reasoning_delta events
 	// with deltaContent are sent as the response is generated.
@@ -909,6 +923,7 @@ type createSessionRequest struct {
 	CustomAgents       []CustomAgentConfig            `json:"customAgents,omitempty"`
 	Agent              string                         `json:"agent,omitempty"`
 	ConfigDir          string                         `json:"configDir,omitempty"`
+	EnableConfigDiscovery *bool                       `json:"enableConfigDiscovery,omitempty"`
 	SkillDirectories   []string                       `json:"skillDirectories,omitempty"`
 	DisabledSkills     []string                       `json:"disabledSkills,omitempty"`
 	InfiniteSessions   *InfiniteSessionConfig         `json:"infiniteSessions,omitempty"`
@@ -948,6 +963,7 @@ type resumeSessionRequest struct {
 	Hooks              *bool                          `json:"hooks,omitempty"`
 	WorkingDirectory   string                         `json:"workingDirectory,omitempty"`
 	ConfigDir          string                         `json:"configDir,omitempty"`
+	EnableConfigDiscovery *bool                       `json:"enableConfigDiscovery,omitempty"`
 	DisableResume      *bool                          `json:"disableResume,omitempty"`
 	Streaming          *bool                          `json:"streaming,omitempty"`
 	MCPServers         map[string]MCPServerConfig     `json:"mcpServers,omitempty"`

nodejs/src/client.ts

@@ -742,6 +742,7 @@ export class CopilotClient {
                 customAgents: config.customAgents,
                 agent: config.agent,
                 configDir: config.configDir,
+                enableConfigDiscovery: config.enableConfigDiscovery,
                 skillDirectories: config.skillDirectories,
                 disabledSkills: config.disabledSkills,
                 infiniteSessions: config.infiniteSessions,
@@ -873,6 +874,7 @@ export class CopilotClient {
                 hooks: !!(config.hooks && Object.values(config.hooks).some(Boolean)),
                 workingDirectory: config.workingDirectory,
                 configDir: config.configDir,
+                enableConfigDiscovery: config.enableConfigDiscovery,
                 streaming: config.streaming,
                 mcpServers: config.mcpServers,
                 envValueMode: "direct",

nodejs/src/types.ts

@@ -1074,6 +1074,19 @@ export interface SessionConfig {
      */
     configDir?: string;
 
+    /**
+     * When true, automatically discovers MCP server configurations (e.g. `.mcp.json`,
+     * `.vscode/mcp.json`) and skill directories from the working directory and merges
+     * them with any explicitly provided `mcpServers` and `skillDirectories`, with
+     * explicit values taking precedence on name collision.
+     *
+     * Note: custom instruction files (`.github/copilot-instructions.md`, `AGENTS.md`, etc.)
+     * are always loaded from the working directory regardless of this setting.
+     *
+     * @default false
+     */
+    enableConfigDiscovery?: boolean;
+
     /**
      * Tools exposed to the CLI server
      */
@@ -1226,6 +1239,7 @@ export type ResumeSessionConfig = Pick<
     | "hooks"
     | "workingDirectory"
     | "configDir"
+    | "enableConfigDiscovery"
     | "mcpServers"
     | "customAgents"
     | "agent"

python/copilot/client.py

@@ -1202,6 +1202,7 @@ async def create_session(
         custom_agents: list[CustomAgentConfig] | None = None,
         agent: str | None = None,
         config_dir: str | None = None,
+        enable_config_discovery: bool | None = None,
         skill_directories: list[str] | None = None,
         disabled_skills: list[str] | None = None,
         infinite_sessions: InfiniteSessionConfig | None = None,
@@ -1238,6 +1239,13 @@ async def create_session(
             custom_agents: Custom agent configurations.
             agent: Agent to use for the session.
             config_dir: Override for the configuration directory.
+            enable_config_discovery: When True, automatically discovers MCP server
+                configurations (e.g. ``.mcp.json``, ``.vscode/mcp.json``) and skill
+                directories from the working directory and merges them with any
+                explicitly provided ``mcp_servers`` and ``skill_directories``, with
+                explicit values taking precedence on name collision. Custom instruction
+                files (``.github/copilot-instructions.md``, ``AGENTS.md``, etc.) are
+                always loaded regardless of this setting.
             skill_directories: Directories to search for skills.
             disabled_skills: Skills to disable.
             infinite_sessions: Infinite session configuration.
@@ -1362,6 +1370,10 @@ async def create_session(
         if config_dir:
             payload["configDir"] = config_dir
 
+        # Add config discovery flag if provided
+        if enable_config_discovery is not None:
+            payload["enableConfigDiscovery"] = enable_config_discovery
+
         # Add skill directories configuration if provided
         if skill_directories:
             payload["skillDirectories"] = skill_directories
@@ -1455,6 +1467,7 @@ async def resume_session(
         custom_agents: list[CustomAgentConfig] | None = None,
         agent: str | None = None,
         config_dir: str | None = None,
+        enable_config_discovery: bool | None = None,
         skill_directories: list[str] | None = None,
         disabled_skills: list[str] | None = None,
         infinite_sessions: InfiniteSessionConfig | None = None,
@@ -1491,6 +1504,13 @@ async def resume_session(
             custom_agents: Custom agent configurations.
             agent: Agent to use for the session.
             config_dir: Override for the configuration directory.
+            enable_config_discovery: When True, automatically discovers MCP server
+                configurations (e.g. ``.mcp.json``, ``.vscode/mcp.json``) and skill
+                directories from the working directory and merges them with any
+                explicitly provided ``mcp_servers`` and ``skill_directories``, with
+                explicit values taking precedence on name collision. Custom instruction
+                files (``.github/copilot-instructions.md``, ``AGENTS.md``, etc.) are
+                always loaded regardless of this setting.
             skill_directories: Directories to search for skills.
             disabled_skills: Skills to disable.
             infinite_sessions: Infinite session configuration.
@@ -1588,6 +1608,8 @@ async def resume_session(
             payload["workingDirectory"] = working_directory
         if config_dir:
             payload["configDir"] = config_dir
+        if enable_config_discovery is not None:
+            payload["enableConfigDiscovery"] = enable_config_discovery
 
         # TODO: disable_resume is not a keyword arg yet; keeping for future use
         if mcp_servers: