Unify realtime v1/v2 session config (#14606)

## Summary
- unify realtime websocket settings under `[realtime]` (`version` and
`type`)
- remove `realtime_conversation_v2` and select parser/session mode from
config

## Testing
- not run (per request)

---------

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

codex-rs/core/src/config/mod.rs

@@ -466,9 +466,9 @@ pub struct Config {
     /// Experimental / do not use. Selects the realtime websocket model/snapshot
     /// used for the `Op::RealtimeConversation` connection.
     pub experimental_realtime_ws_model: Option<String>,
-    /// Experimental / do not use. Selects the realtime websocket intent mode.
-    /// `conversational` is speech-to-speech while `transcription` is transcript-only.
-    pub experimental_realtime_ws_mode: RealtimeWsMode,
+    /// Experimental / do not use. Realtime websocket session selection.
+    /// `version` controls v1/v2 and `type` controls conversational/transcription.
+    pub realtime: RealtimeConfig,
     /// Experimental / do not use. Overrides only the realtime conversation
     /// websocket transport instructions (the `Op::RealtimeConversation`
     /// `/ws` session.update instructions) without changing normal prompts.
@@ -1244,9 +1244,10 @@ pub struct ConfigToml {
     /// Experimental / do not use. Selects the realtime websocket model/snapshot
     /// used for the `Op::RealtimeConversation` connection.
     pub experimental_realtime_ws_model: Option<String>,
-    /// Experimental / do not use. Selects the realtime websocket intent mode.
-    /// `conversational` is speech-to-speech while `transcription` is transcript-only.
-    pub experimental_realtime_ws_mode: Option<RealtimeWsMode>,
+    /// Experimental / do not use. Realtime websocket session selection.
+    /// `version` controls v1/v2 and `type` controls conversational/transcription.
+    #[serde(default)]
+    pub realtime: Option<RealtimeToml>,
     /// Experimental / do not use. Overrides only the realtime conversation
     /// websocket transport instructions (the `Op::RealtimeConversation`
     /// `/ws` session.update instructions) without changing normal prompts.
@@ -1400,6 +1401,30 @@ pub enum RealtimeWsMode {
     Transcription,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, Copy, Default, PartialEq, Eq, JsonSchema)]
+#[serde(rename_all = "snake_case")]
+pub enum RealtimeWsVersion {
+    #[default]
+    V1,
+    V2,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, Default, PartialEq, Eq, JsonSchema)]
+#[schemars(deny_unknown_fields)]
+pub struct RealtimeConfig {
+    pub version: RealtimeWsVersion,
+    #[serde(rename = "type")]
+    pub session_type: RealtimeWsMode,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, Default, PartialEq, Eq, JsonSchema)]
+#[schemars(deny_unknown_fields)]
+pub struct RealtimeToml {
+    pub version: Option<RealtimeWsVersion>,
+    #[serde(rename = "type")]
+    pub session_type: Option<RealtimeWsMode>,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, Default, PartialEq, Eq, JsonSchema)]
 #[schemars(deny_unknown_fields)]
 pub struct RealtimeAudioToml {
@@ -2482,7 +2507,12 @@ impl Config {
                 }),
             experimental_realtime_ws_base_url: cfg.experimental_realtime_ws_base_url,
             experimental_realtime_ws_model: cfg.experimental_realtime_ws_model,
-            experimental_realtime_ws_mode: cfg.experimental_realtime_ws_mode.unwrap_or_default(),
+            realtime: cfg
+                .realtime
+                .map_or_else(RealtimeConfig::default, |realtime| RealtimeConfig {
+                    version: realtime.version.unwrap_or_default(),
+                    session_type: realtime.session_type.unwrap_or_default(),
+                }),
             experimental_realtime_ws_backend_prompt: cfg.experimental_realtime_ws_backend_prompt,
             experimental_realtime_ws_startup_context: cfg.experimental_realtime_ws_startup_context,
             experimental_realtime_start_instructions: cfg.experimental_realtime_start_instructions,