realtime: rename provider session ids (#20361)

## Summary

Codex is repurposing `session` to mean a thread group, so the realtime
provider session id should no longer use `session_id` / `sessionId` in
Codex-facing protocol payloads. This PR renames that provider-specific
field to `realtime_session_id` / `realtimeSessionId` and intentionally
breaks clients that still send the old field names.

## What Changed

- Renamed realtime provider session fields in `ConversationStartParams`,
`RealtimeConversationStartedEvent`, and `RealtimeEvent::SessionUpdated`.
- Renamed app-server v2 realtime request and notification fields to
`realtimeSessionId`.
- Removed legacy serde aliases for `session_id` / `sessionId`; clients
must send the new names.
- Propagated the rename through core realtime startup, app-server
adapters, codex-api websocket handling, and TUI realtime state.
- Regenerated app-server protocol schema/TypeScript outputs and updated
app-server README examples.
- Kept upstream Realtime API concepts unchanged: provider `session.id`
parsing and `x-session-id` headers still use the upstream wire names.

## Testing

- CI is running on the latest pushed commit.
- Earlier local verification on this PR:
  - `cargo test -p codex-protocol`
- `CODEX_SKIP_VENDORED_BWRAP=1 cargo test -p codex-core
realtime_conversation`
  - `cargo test -p codex-app-server-protocol`
- `CODEX_SKIP_VENDORED_BWRAP=1 cargo test -p codex-app-server
realtime_conversation`
- attempted `CODEX_SKIP_VENDORED_BWRAP=1 cargo test -p codex-tui` (local
linker bus error while linking the test binary)

---------

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

codex-rs/app-server/README.md

@@ -761,14 +761,14 @@ const offer = await pc.createOffer();
 await pc.setLocalDescription(offer);
 ```
 
-Then send `offer.sdp` to app-server. Core uses `experimental_realtime_ws_backend_prompt` for the backend instructions and the thread conversation id for the realtime session id. The start response is `{}`; the remote answer SDP arrives later as `thread/realtime/sdp` and should be passed to `setRemoteDescription()`:
+Then send `offer.sdp` to app-server. Core uses `experimental_realtime_ws_backend_prompt` for the backend instructions and the thread conversation id as the default Realtime API session identifier. This `realtimeSessionId` value refers to the upstream Realtime API session, not a Codex session/thread-group id. The start response is `{}`; the remote answer SDP arrives later as `thread/realtime/sdp` and should be passed to `setRemoteDescription()`:
 
 ```json
 { "method": "thread/realtime/start", "id": 40, "params": {
     "threadId": "thr_123",
     "outputModality": "audio",
     "prompt": "You are on a call.",
-    "sessionId": null,
+    "realtimeSessionId": null,
     "transport": { "type": "webrtc", "sdp": "v=0\r\no=..." }
 } }
 { "id": 40, "result": {} }
@@ -1100,7 +1100,7 @@ The fuzzy file search session API emits per-query notifications:
 
 The thread realtime API emits thread-scoped notifications for session lifecycle and streaming media:
 
-- `thread/realtime/started` — `{ threadId, sessionId }` once realtime starts for the thread (experimental).
+- `thread/realtime/started` — `{ threadId, realtimeSessionId }` once realtime starts for the thread (experimental). `realtimeSessionId` is the upstream Realtime API session identifier, not a Codex session/thread-group id.
 - `thread/realtime/itemAdded` — `{ threadId, item }` for raw non-audio realtime items that do not have a dedicated typed app-server notification, including `handoff_request` (experimental). `item` is forwarded as raw JSON while the upstream websocket item schema remains unstable.
 - `thread/realtime/transcript/delta` — `{ threadId, role, delta }` for live realtime transcript deltas (experimental).
 - `thread/realtime/transcript/done` — `{ threadId, role, text }` when realtime emits the final full text for a transcript part (experimental).

codex-rs/app-server/src/bespoke_event_handling.rs

@@ -387,7 +387,7 @@ pub(crate) async fn apply_bespoke_event_handling(
         EventMsg::RealtimeConversationStarted(event) => {
             let notification = ThreadRealtimeStartedNotification {
                 thread_id: conversation_id.to_string(),
-                session_id: event.session_id,
+                realtime_session_id: event.realtime_session_id,
                 version: event.version,
             };
             outgoing

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

@@ -6994,7 +6994,7 @@ impl CodexMessageProcessor {
                 Op::RealtimeConversationStart(ConversationStartParams {
                     output_modality: params.output_modality,
                     prompt: params.prompt,
-                    session_id: params.session_id,
+                    realtime_session_id: params.realtime_session_id,
                     transport: params.transport.map(|transport| match transport {
                         ThreadRealtimeStartTransport::Websocket => {
                             ConversationStartTransport::Websocket

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

@@ -79,7 +79,7 @@ async fn realtime_conversation_start_requires_experimental_api_capability() -> R
             thread_id: "thr_123".to_string(),
             output_modality: RealtimeOutputModality::Audio,
             prompt: Some(Some("hello".to_string())),
-            session_id: None,
+            realtime_session_id: None,
             transport: None,
             voice: None,
         })
@@ -149,7 +149,7 @@ async fn realtime_webrtc_start_requires_experimental_api_capability() -> Result<
             thread_id: "thr_123".to_string(),
             output_modality: RealtimeOutputModality::Audio,
             prompt: Some(Some("hello".to_string())),
-            session_id: None,
+            realtime_session_id: None,
             transport: Some(ThreadRealtimeStartTransport::Webrtc {
                 sdp: "v=offer\r\n".to_string(),
             }),

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

@@ -313,7 +313,7 @@ impl RealtimeE2eHarness {
                 thread_id: self.thread_id.clone(),
                 output_modality: RealtimeOutputModality::Audio,
                 prompt: Some(Some("backend prompt".to_string())),
-                session_id: None,
+                realtime_session_id: None,
                 transport: Some(ThreadRealtimeStartTransport::Webrtc {
                     sdp: offer_sdp.to_string(),
                 }),
@@ -440,10 +440,10 @@ fn open_realtime_sideband_connection(
     }
 }
 
-fn session_updated(session_id: &str) -> Value {
+fn session_updated(realtime_session_id: &str) -> Value {
     json!({
         "type": "session.updated",
-        "session": { "id": session_id, "instructions": "backend prompt" }
+        "session": { "id": realtime_session_id, "instructions": "backend prompt" }
     })
 }
 
@@ -558,7 +558,7 @@ async fn realtime_conversation_streams_v2_notifications() -> Result<()> {
             thread_id: thread_start.thread.id.clone(),
             output_modality: RealtimeOutputModality::Audio,
             prompt: None,
-            session_id: None,
+            realtime_session_id: None,
             transport: None,
             voice: Some(RealtimeVoice::Cedar),
         })
@@ -574,7 +574,7 @@ async fn realtime_conversation_streams_v2_notifications() -> Result<()> {
         read_notification::<ThreadRealtimeStartedNotification>(&mut mcp, "thread/realtime/started")
             .await?;
     assert_eq!(started.thread_id, thread_start.thread.id);
-    assert!(started.session_id.is_some());
+    assert!(started.realtime_session_id.is_some());
     assert_eq!(started.version, RealtimeConversationVersion::V2);
 
     let startup_context_request = realtime_server
@@ -807,7 +807,7 @@ async fn realtime_text_output_modality_requests_text_output_and_final_transcript
             thread_id: thread_start.thread.id.clone(),
             output_modality: RealtimeOutputModality::Text,
             prompt: None,
-            session_id: None,
+            realtime_session_id: None,
             transport: None,
             voice: None,
         })
@@ -981,7 +981,7 @@ async fn realtime_conversation_stop_emits_closed_notification() -> Result<()> {
             thread_id: thread_start.thread.id.clone(),
             output_modality: RealtimeOutputModality::Audio,
             prompt: Some(Some("backend prompt".to_string())),
-            session_id: None,
+            realtime_session_id: None,
             transport: None,
             voice: None,
         })
@@ -1078,7 +1078,7 @@ async fn realtime_webrtc_start_emits_sdp_notification() -> Result<()> {
             thread_id: thread_id.clone(),
             output_modality: RealtimeOutputModality::Audio,
             prompt: Some(Some("backend prompt".to_string())),
-            session_id: None,
+            realtime_session_id: None,
             transport: Some(ThreadRealtimeStartTransport::Webrtc {
                 sdp: "v=offer\r\n".to_string(),
             }),
@@ -1208,7 +1208,7 @@ async fn webrtc_v1_start_posts_offer_returns_sdp_and_joins_sideband() -> Result<
         StartedWebrtcRealtime {
             started: ThreadRealtimeStartedNotification {
                 thread_id: harness.thread_id.clone(),
-                session_id: Some(harness.thread_id.clone()),
+                realtime_session_id: Some(harness.thread_id.clone()),
                 version: RealtimeConversationVersion::V1,
             },
             sdp: ThreadRealtimeSdpNotification {
@@ -1993,7 +1993,7 @@ async fn realtime_webrtc_start_surfaces_backend_error() -> Result<()> {
             thread_id: thread_start.thread.id,
             output_modality: RealtimeOutputModality::Audio,
             prompt: Some(Some("backend prompt".to_string())),
-            session_id: None,
+            realtime_session_id: None,
             transport: Some(ThreadRealtimeStartTransport::Webrtc {
                 sdp: "v=offer\r\n".to_string(),
             }),
@@ -2052,7 +2052,7 @@ async fn realtime_conversation_requires_feature_flag() -> Result<()> {
             thread_id: thread_start.thread.id.clone(),
             output_modality: RealtimeOutputModality::Audio,
             prompt: Some(Some("backend prompt".to_string())),
-            session_id: None,
+            realtime_session_id: None,
             transport: None,
             voice: None,
         })