[mcp-server] Add GetConfig endpoint (#2725)

## Summary
Adds a GetConfig request to the MCP Protocol, so MCP clients can
evaluate the resolved config.toml settings which the harness is using.

## Testing
- [x] Added an end to end test of the endpoint

codex-rs/protocol/src/config_types.rs

@@ -4,6 +4,8 @@ use strum_macros::Display;
 use strum_macros::EnumIter;
 use ts_rs::TS;
 
+use crate::protocol::AskForApproval;
+
 /// See https://platform.openai.com/docs/guides/reasoning?api-mode=responses#get-started-with-reasoning
 #[derive(
     Debug, Serialize, Deserialize, Default, Clone, Copy, PartialEq, Eq, Display, TS, EnumIter,
@@ -47,3 +49,13 @@ pub enum SandboxMode {
     #[serde(rename = "danger-full-access")]
     DangerFullAccess,
 }
+
+/// Collection of common configuration options that a user can define as a unit
+/// in `config.toml`. Currently only a subset of the fields are supported.
+#[derive(Deserialize, Debug, Clone, PartialEq, Serialize, TS)]
+#[serde(rename_all = "camelCase")]
+pub struct ConfigProfile {
+    pub model: Option<String>,
+    pub approval_policy: Option<AskForApproval>,
+    pub model_reasoning_effort: Option<ReasoningEffort>,
+}

codex-rs/protocol/src/mcp_protocol.rs

@@ -2,6 +2,7 @@ use std::collections::HashMap;
 use std::fmt::Display;
 use std::path::PathBuf;
 
+use crate::config_types::ConfigProfile;
 use crate::config_types::ReasoningEffort;
 use crate::config_types::ReasoningSummary;
 use crate::config_types::SandboxMode;
@@ -101,6 +102,10 @@ pub enum ClientRequest {
         request_id: RequestId,
         params: GetAuthStatusParams,
     },
+    GetConfigToml {
+        #[serde(rename = "id")]
+        request_id: RequestId,
+    },
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Default, TS)]
@@ -223,6 +228,26 @@ pub struct GetAuthStatusResponse {
     pub auth_token: Option<String>,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, TS)]
+#[serde(rename_all = "camelCase")]
+pub struct GetConfigTomlResponse {
+    /// Approvals
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub approval_policy: Option<AskForApproval>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub sandbox_mode: Option<SandboxMode>,
+
+    /// Relevant model configuration
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub model_reasoning_effort: Option<ReasoningEffort>,
+
+    /// Profiles
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub profile: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub profiles: Option<HashMap<String, ConfigProfile>>,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, TS)]
 #[serde(rename_all = "camelCase")]
 pub struct SendUserMessageParams {