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-protocol/src/protocol/common.rs

@@ -2558,7 +2558,7 @@ mod tests {
                 thread_id: "thr_123".to_string(),
                 output_modality: RealtimeOutputModality::Audio,
                 prompt: Some(Some("You are on a call".to_string())),
-                session_id: Some("sess_456".to_string()),
+                realtime_session_id: Some("sess_456".to_string()),
                 transport: None,
                 voice: Some(RealtimeVoice::Marin),
             },
@@ -2571,7 +2571,7 @@ mod tests {
                     "threadId": "thr_123",
                     "outputModality": "audio",
                     "prompt": "You are on a call",
-                    "sessionId": "sess_456",
+                    "realtimeSessionId": "sess_456",
                     "transport": null,
                     "voice": "marin"
                 }
@@ -2589,7 +2589,7 @@ mod tests {
                 thread_id: "thr_123".to_string(),
                 output_modality: RealtimeOutputModality::Audio,
                 prompt: None,
-                session_id: None,
+                realtime_session_id: None,
                 transport: None,
                 voice: None,
             },
@@ -2601,7 +2601,7 @@ mod tests {
                 "params": {
                     "threadId": "thr_123",
                     "outputModality": "audio",
-                    "sessionId": null,
+                    "realtimeSessionId": null,
                     "transport": null,
                     "voice": null
                 }
@@ -2615,7 +2615,7 @@ mod tests {
                 thread_id: "thr_123".to_string(),
                 output_modality: RealtimeOutputModality::Audio,
                 prompt: Some(None),
-                session_id: None,
+                realtime_session_id: None,
                 transport: None,
                 voice: None,
             },
@@ -2628,7 +2628,7 @@ mod tests {
                     "threadId": "thr_123",
                     "outputModality": "audio",
                     "prompt": null,
-                    "sessionId": null,
+                    "realtimeSessionId": null,
                     "transport": null,
                     "voice": null
                 }
@@ -2642,7 +2642,7 @@ mod tests {
             "params": {
                 "threadId": "thr_123",
                 "outputModality": "audio",
-                "sessionId": null,
+                "realtimeSessionId": null,
                 "transport": null,
                 "voice": null
             }
@@ -2659,7 +2659,7 @@ mod tests {
                 "threadId": "thr_123",
                 "outputModality": "audio",
                 "prompt": null,
-                "sessionId": null,
+                "realtimeSessionId": null,
                 "transport": null,
                 "voice": null
             }
@@ -2771,7 +2771,7 @@ mod tests {
                 thread_id: "thr_123".to_string(),
                 output_modality: RealtimeOutputModality::Audio,
                 prompt: Some(Some("You are on a call".to_string())),
-                session_id: None,
+                realtime_session_id: None,
                 transport: None,
                 voice: None,
             },
@@ -2854,7 +2854,7 @@ mod tests {
         let notification =
             ServerNotification::ThreadRealtimeStarted(v2::ThreadRealtimeStartedNotification {
                 thread_id: "thr_123".to_string(),
-                session_id: Some("sess_456".to_string()),
+                realtime_session_id: Some("sess_456".to_string()),
                 version: RealtimeConversationVersion::V1,
             });
         let reason = crate::experimental_api::ExperimentalApi::experimental_reason(&notification);

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -5293,7 +5293,7 @@ pub struct ThreadRealtimeStartParams {
     #[ts(optional = nullable)]
     pub prompt: Option<Option<String>>,
     #[ts(optional = nullable)]
-    pub session_id: Option<String>,
+    pub realtime_session_id: Option<String>,
     #[ts(optional = nullable)]
     pub transport: Option<ThreadRealtimeStartTransport>,
     #[ts(optional = nullable)]
@@ -5383,7 +5383,7 @@ pub struct ThreadRealtimeListVoicesResponse {
 #[ts(export_to = "v2/")]
 pub struct ThreadRealtimeStartedNotification {
     pub thread_id: String,
-    pub session_id: Option<String>,
+    pub realtime_session_id: Option<String>,
     pub version: RealtimeConversationVersion,
 }