feat: introduce ClientRequest::SendUserTurn (#2345)

This adds a new request type, `SendUserTurn`, that makes it possible to
submit a `Op::UserTurn` operation (introduced in #2329) to a
conversation. This PR also adds a new integration test that verifies
that changing from `AskForApproval::UnlessTrusted` to
`AskForApproval::Never` mid-conversation ensures that an elicitation is
no longer sent for running `python3 -c print(42)`.

---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/2345).
* __->__ #2345
* #2329
* #2343
* #2340
* #2338

codex-rs/mcp-server/src/wire_format.rs

@@ -2,8 +2,12 @@ use std::collections::HashMap;
 use std::fmt::Display;
 use std::path::PathBuf;
 
+use codex_core::config_types::ReasoningEffort;
+use codex_core::config_types::ReasoningSummary;
+use codex_core::protocol::AskForApproval;
 use codex_core::protocol::FileChange;
 use codex_core::protocol::ReviewDecision;
+use codex_core::protocol::SandboxPolicy;
 use mcp_types::RequestId;
 use serde::Deserialize;
 use serde::Serialize;
@@ -36,6 +40,11 @@ pub enum ClientRequest {
         request_id: RequestId,
         params: SendUserMessageParams,
     },
+    SendUserTurn {
+        #[serde(rename = "id")]
+        request_id: RequestId,
+        params: SendUserTurnParams,
+    },
     InterruptConversation {
         #[serde(rename = "id")]
         request_id: RequestId,
@@ -120,6 +129,23 @@ pub struct SendUserMessageParams {
     pub items: Vec<InputItem>,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
+#[serde(rename_all = "camelCase")]
+pub struct SendUserTurnParams {
+    pub conversation_id: ConversationId,
+    pub items: Vec<InputItem>,
+    pub cwd: PathBuf,
+    pub approval_policy: AskForApproval,
+    pub sandbox_policy: SandboxPolicy,
+    pub model: String,
+    pub effort: ReasoningEffort,
+    pub summary: ReasoningSummary,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
+#[serde(rename_all = "camelCase")]
+pub struct SendUserTurnResponse {}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
 #[serde(rename_all = "camelCase")]
 pub struct InterruptConversationParams {