Struct CopilotHeadlessConfig 

pub struct CopilotHeadlessConfig {
    pub cli_path: Option<PathBuf>,
    pub working_directory: Option<PathBuf>,
    pub model: String,
    pub github_token: Option<String>,
    pub permission_policy: PermissionPolicy,
    pub max_history_turns: usize,
    pub mcp_tool_calling: bool,
    pub reasoning_effort: Option<ReasoningEffort>,
    pub builtin_tools: bool,
}

Configuration for the Copilot Headless (ACP) provider.

Fields

cli_path: Option<PathBuf>

Override path to the copilot CLI binary (default: auto-detect via PATH).

working_directory: Option<PathBuf>

Directory every copilot --acp subprocess runs in and the cwd of every session it serves. Copilot treats that directory as the project — it loads .mcp.json, agent files and custom instructions from it — so a host that sets this hands the model that project. A relative path is anchored to the host’s cwd. Unset, the runner uses a scratch directory under the system temp dir, not the host process’s working directory.

model: String

Default model to use for completions.

github_token: Option<String>

GitHub token for authentication (optional, uses stored OAuth by default).

permission_policy: PermissionPolicy

Policy for handling permission requests from the copilot subprocess.

max_history_turns: usize

Maximum number of prior conversation messages (user + assistant) to include in the ACP prompt for multi-turn context. Set to 0 to disable history injection.

mcp_tool_calling: bool

Advertise SDK_TOOL_CALLING so callers route tool turns through the ACP converse() loop with per-request MCP servers (native tool calling), instead of falling through to text-based <tool_call> parsing. The caller must pass mcp_servers on each request for tools to be reachable. Default: false.

reasoning_effort: Option<ReasoningEffort>

Reasoning effort every copilot --acp child is launched with (--reasoning-effort). None takes the model’s family default (crate::copilot_models::default_effort_for); a model with no known default gets no flag, and then the CLI uses the effortLevel in the host user’s ~/.copilot/settings.json, which can be high.

Reasoning is billed as output and is most of a short turn’s time: one snippet on claude-haiku-5.5 (CLI 1.0.108) took 5.8 s and 1,093 output tokens, 895 of them reasoning, at high, and 0.9 s, 65 tokens and no reasoning at low.

builtin_tools: bool

Keep the Copilot CLI’s built-in tools (bash, view, edit, glob, grep, web_fetch, …) available to the model. Default: false.

Off, the child is launched with --available-tools mcp:* task_complete: the MCP servers a request brings stay callable, Autopilot keeps the tool it ends a run with, and nothing else is offered. The built-ins’ schemas are most of what Copilot adds to every prompt: a plain completion measured 21,149 prompt tokens with them and 4,003 without (CLI 1.0.108). Under PermissionPolicy::DenyAll the model could only reach the ones that need no permission, and those read the session directory.

Implementations

impl CopilotHeadlessConfig

pub fn from_env() -> Self

Create configuration from environment variables.

Environment variables:

• COPILOT_CLI_PATH — Override path to copilot binary
• COPILOT_HEADLESS_WORKING_DIR — Directory the subprocess and its sessions run in (default: a scratch directory under the system temp dir)
• COPILOT_HEADLESS_MODEL — Default model (defaults to the top-ranked candidate in crate::copilot_models::CATALOG)
• COPILOT_GITHUB_TOKEN / GH_TOKEN / GITHUB_TOKEN — GitHub auth token
• COPILOT_HEADLESS_MAX_HISTORY_TURNS — Max conversation history turns (default: 20)
• COPILOT_HEADLESS_MCP_TOOL_CALLING — Advertise SDK_TOOL_CALLING for native ACP MCP tool calling (default: false)
• COPILOT_HEADLESS_REASONING_EFFORT — low, medium, high or xhigh (default: the model’s family default; an unknown value is ignored with a warning)
• COPILOT_HEADLESS_BUILTIN_TOOLS — Keep the CLI’s built-in tools (default: true when the permission policy approves tool calls, false otherwise)

Trait Implementations

impl Clone for CopilotHeadlessConfig

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for CopilotHeadlessConfig

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for CopilotHeadlessConfig

fn default() -> Self

Returns the “default value” for a type.