Add WebRTC transport to realtime start (#16960)

Adds WebRTC startup to the experimental app-server
`thread/realtime/start` method with an optional transport enum. The
websocket path remains the default; WebRTC offers create the realtime
session through the shared start flow and emit the answer SDP via
`thread/realtime/sdp`.

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/tui/src/app/app_server_adapter.rs

@@ -391,6 +391,9 @@ fn server_notification_thread_target(
         ServerNotification::ThreadRealtimeOutputAudioDelta(notification) => {
             Some(notification.thread_id.as_str())
         }
+        ServerNotification::ThreadRealtimeSdp(notification) => {
+            Some(notification.thread_id.as_str())
+        }
         ServerNotification::ThreadRealtimeError(notification) => {
             Some(notification.thread_id.as_str())
         }
@@ -625,6 +628,17 @@ fn server_notification_thread_events(
                 }),
             }],
         )),
+        ServerNotification::ThreadRealtimeSdp(notification) => Some((
+            ThreadId::from_string(&notification.thread_id).ok()?,
+            vec![Event {
+                id: String::new(),
+                msg: EventMsg::RealtimeConversationSdp(
+                    codex_protocol::protocol::RealtimeConversationSdpEvent {
+                        sdp: notification.sdp,
+                    },
+                ),
+            }],
+        )),
         ServerNotification::ThreadRealtimeError(notification) => Some((
             ThreadId::from_string(&notification.thread_id).ok()?,
             vec![Event {

codex-rs/tui/src/app_server_session.rs

@@ -42,6 +42,7 @@ use codex_app_server_protocol::ThreadRealtimeAppendTextParams;
 use codex_app_server_protocol::ThreadRealtimeAppendTextResponse;
 use codex_app_server_protocol::ThreadRealtimeStartParams;
 use codex_app_server_protocol::ThreadRealtimeStartResponse;
+use codex_app_server_protocol::ThreadRealtimeStartTransport;
 use codex_app_server_protocol::ThreadRealtimeStopParams;
 use codex_app_server_protocol::ThreadRealtimeStopResponse;
 use codex_app_server_protocol::ThreadResumeParams;
@@ -76,6 +77,7 @@ use codex_protocol::openai_models::ReasoningEffortPreset;
 use codex_protocol::protocol::AskForApproval;
 use codex_protocol::protocol::ConversationAudioParams;
 use codex_protocol::protocol::ConversationStartParams;
+use codex_protocol::protocol::ConversationStartTransport;
 use codex_protocol::protocol::ConversationTextParams;
 use codex_protocol::protocol::CreditsSnapshot;
 use codex_protocol::protocol::RateLimitSnapshot;
@@ -660,6 +662,14 @@ impl AppServerSession {
                     thread_id: thread_id.to_string(),
                     prompt: params.prompt,
                     session_id: params.session_id,
+                    transport: params.transport.map(|transport| match transport {
+                        ConversationStartTransport::Websocket => {
+                            ThreadRealtimeStartTransport::Websocket
+                        }
+                        ConversationStartTransport::Webrtc { sdp } => {
+                            ThreadRealtimeStartTransport::Webrtc { sdp }
+                        }
+                    }),
                 },
             })
             .await

codex-rs/tui/src/chatwidget.rs

@@ -6501,6 +6501,7 @@ impl ChatWidget {
                     );
                 }
             }
+            ServerNotification::ThreadRealtimeSdp(_) => {}
             ServerNotification::ServerRequestResolved(_)
             | ServerNotification::AccountUpdated(_)
             | ServerNotification::AccountRateLimitsUpdated(_)
@@ -7020,6 +7021,7 @@ impl ChatWidget {
                     self.on_realtime_conversation_started(ev);
                 }
             }
+            EventMsg::RealtimeConversationSdp(_) => {}
             EventMsg::RealtimeConversationRealtime(ev) => {
                 if !from_replay {
                     self.on_realtime_conversation_realtime(ev);

codex-rs/tui/src/chatwidget/realtime.rs

@@ -229,6 +229,7 @@ impl ChatWidget {
             ConversationStartParams {
                 prompt: REALTIME_CONVERSATION_PROMPT.to_string(),
                 session_id: None,
+                transport: None,
             },
         ));
         self.request_redraw();