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/codex-api/src/endpoint/realtime_websocket/methods.rs

@@ -858,7 +858,7 @@ mod tests {
         assert_eq!(
             parse_realtime_event(payload.as_str(), RealtimeEventParser::V1),
             Some(RealtimeEvent::SessionUpdated {
-                session_id: "sess_123".to_string(),
+                realtime_session_id: "sess_123".to_string(),
                 instructions: Some("backend prompt".to_string()),
             })
         );
@@ -1698,7 +1698,7 @@ mod tests {
         assert_eq!(
             created,
             RealtimeEvent::SessionUpdated {
-                session_id: "sess_mock".to_string(),
+                realtime_session_id: "sess_mock".to_string(),
                 instructions: Some("backend prompt".to_string()),
             }
         );
@@ -1992,7 +1992,7 @@ mod tests {
         assert_eq!(
             created,
             RealtimeEvent::SessionUpdated {
-                session_id: "sess_v2".to_string(),
+                realtime_session_id: "sess_v2".to_string(),
                 instructions: Some("backend prompt".to_string()),
             }
         );
@@ -2107,7 +2107,7 @@ mod tests {
         assert_eq!(
             created,
             RealtimeEvent::SessionUpdated {
-                session_id: "sess_transcription".to_string(),
+                realtime_session_id: "sess_transcription".to_string(),
                 instructions: None,
             }
         );
@@ -2211,7 +2211,7 @@ mod tests {
         assert_eq!(
             created,
             RealtimeEvent::SessionUpdated {
-                session_id: "sess_v1_mode".to_string(),
+                realtime_session_id: "sess_v1_mode".to_string(),
                 instructions: None,
             }
         );
@@ -2317,7 +2317,7 @@ mod tests {
         assert_eq!(
             next_event,
             RealtimeEvent::SessionUpdated {
-                session_id: "sess_after_send".to_string(),
+                realtime_session_id: "sess_after_send".to_string(),
                 instructions: Some("backend prompt".to_string()),
             }
         );

codex-rs/codex-api/src/endpoint/realtime_websocket/protocol_common.rs

@@ -38,7 +38,7 @@ pub(super) fn parse_session_updated_event(parsed: &Value) -> Option<RealtimeEven
         .and_then(Value::as_str)
         .map(str::to_string);
     Some(RealtimeEvent::SessionUpdated {
-        session_id,
+        realtime_session_id: session_id,
         instructions,
     })
 }