fix(app-server): set originator header from initialize (re-revert) (#8988)

Reapplies https://github.com/openai/codex/pull/8873 which was reverted
due to merge conflicts

codex-rs/app-server/tests/suite/v2/turn_start.rs

@@ -8,6 +8,7 @@ use app_test_support::create_mock_responses_server_sequence_unchecked;
 use app_test_support::create_shell_command_sse_response;
 use app_test_support::format_with_current_shell_display;
 use app_test_support::to_response;
+use codex_app_server_protocol::ClientInfo;
 use codex_app_server_protocol::CommandExecutionApprovalDecision;
 use codex_app_server_protocol::CommandExecutionRequestApprovalResponse;
 use codex_app_server_protocol::CommandExecutionStatus;
@@ -40,6 +41,76 @@ use tempfile::TempDir;
 use tokio::time::timeout;
 
 const DEFAULT_READ_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(10);
+const TEST_ORIGINATOR: &str = "codex_vscode";
+
+#[tokio::test]
+async fn turn_start_sends_originator_header() -> Result<()> {
+    let responses = vec![create_final_assistant_message_sse_response("Done")?];
+    let server = create_mock_responses_server_sequence_unchecked(responses).await;
+
+    let codex_home = TempDir::new()?;
+    create_config_toml(codex_home.path(), &server.uri(), "never")?;
+
+    let mut mcp = McpProcess::new(codex_home.path()).await?;
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.initialize_with_client_info(ClientInfo {
+            name: TEST_ORIGINATOR.to_string(),
+            title: Some("Codex VS Code Extension".to_string()),
+            version: "0.1.0".to_string(),
+        }),
+    )
+    .await??;
+
+    let thread_req = mcp
+        .send_thread_start_request(ThreadStartParams {
+            model: Some("mock-model".to_string()),
+            ..Default::default()
+        })
+        .await?;
+    let thread_resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(thread_req)),
+    )
+    .await??;
+    let ThreadStartResponse { thread, .. } = to_response::<ThreadStartResponse>(thread_resp)?;
+
+    let turn_req = mcp
+        .send_turn_start_request(TurnStartParams {
+            thread_id: thread.id.clone(),
+            input: vec![V2UserInput::Text {
+                text: "Hello".to_string(),
+            }],
+            ..Default::default()
+        })
+        .await?;
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(turn_req)),
+    )
+    .await??;
+
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("turn/completed"),
+    )
+    .await??;
+
+    let requests = server
+        .received_requests()
+        .await
+        .expect("failed to fetch received requests");
+    assert!(!requests.is_empty());
+    for request in requests {
+        let originator = request
+            .headers
+            .get("originator")
+            .expect("originator header missing");
+        assert_eq!(originator.to_str()?, TEST_ORIGINATOR);
+    }
+
+    Ok(())
+}
 
 #[tokio::test]
 async fn turn_start_emits_notifications_and_accepts_model_override() -> Result<()> {