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)
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with [ReviewStack](https://reviewstack.dev/openai/codex/pull/2345).
* __->__ #2345
* #2329
* #2343
* #2340
* #2338

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

@@ -42,6 +42,8 @@ use crate::wire_format::RemoveConversationListenerParams;
 use crate::wire_format::RemoveConversationSubscriptionResponse;
 use crate::wire_format::SendUserMessageParams;
 use crate::wire_format::SendUserMessageResponse;
+use crate::wire_format::SendUserTurnParams;
+use crate::wire_format::SendUserTurnResponse;
 use codex_core::protocol::InputItem as CoreInputItem;
 use codex_core::protocol::Op;
 
@@ -78,6 +80,9 @@ impl CodexMessageProcessor {
             ClientRequest::SendUserMessage { request_id, params } => {
                 self.send_user_message(request_id, params).await;
             }
+            ClientRequest::SendUserTurn { request_id, params } => {
+                self.send_user_turn(request_id, params).await;
+            }
             ClientRequest::InterruptConversation { request_id, params } => {
                 self.interrupt_conversation(request_id, params).await;
             }
@@ -169,6 +174,58 @@ impl CodexMessageProcessor {
             .await;
     }
 
+    async fn send_user_turn(&self, request_id: RequestId, params: SendUserTurnParams) {
+        let SendUserTurnParams {
+            conversation_id,
+            items,
+            cwd,
+            approval_policy,
+            sandbox_policy,
+            model,
+            effort,
+            summary,
+        } = params;
+
+        let Ok(conversation) = self
+            .conversation_manager
+            .get_conversation(conversation_id.0)
+            .await
+        else {
+            let error = JSONRPCErrorError {
+                code: INVALID_REQUEST_ERROR_CODE,
+                message: format!("conversation not found: {conversation_id}"),
+                data: None,
+            };
+            self.outgoing.send_error(request_id, error).await;
+            return;
+        };
+
+        let mapped_items: Vec<CoreInputItem> = items
+            .into_iter()
+            .map(|item| match item {
+                WireInputItem::Text { text } => CoreInputItem::Text { text },
+                WireInputItem::Image { image_url } => CoreInputItem::Image { image_url },
+                WireInputItem::LocalImage { path } => CoreInputItem::LocalImage { path },
+            })
+            .collect();
+
+        let _ = conversation
+            .submit(Op::UserTurn {
+                items: mapped_items,
+                cwd,
+                approval_policy,
+                sandbox_policy,
+                model,
+                effort,
+                summary,
+            })
+            .await;
+
+        self.outgoing
+            .send_response(request_id, SendUserTurnResponse {})
+            .await;
+    }
+
     async fn interrupt_conversation(
         &mut self,
         request_id: RequestId,