Add realtime output modality and transcript events (#17701)

- Add outputModality to thread/realtime/start and wire text/audio output
selection through app-server, core, API, and TUI.\n- Rename the realtime
transcript delta notification and add a separate transcript done
notification that forwards final text from item done without correlating
it with deltas.

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -4379,20 +4379,40 @@
           "properties": {
             "method": {
               "enum": [
-                "thread/realtime/transcriptUpdated"
+                "thread/realtime/transcript/delta"
               ],
-              "title": "Thread/realtime/transcriptUpdatedNotificationMethod",
+              "title": "Thread/realtime/transcript/deltaNotificationMethod",
               "type": "string"
             },
             "params": {
-              "$ref": "#/definitions/v2/ThreadRealtimeTranscriptUpdatedNotification"
+              "$ref": "#/definitions/v2/ThreadRealtimeTranscriptDeltaNotification"
             }
           },
           "required": [
             "method",
             "params"
           ],
-          "title": "Thread/realtime/transcriptUpdatedNotification",
+          "title": "Thread/realtime/transcript/deltaNotification",
+          "type": "object"
+        },
+        {
+          "properties": {
+            "method": {
+              "enum": [
+                "thread/realtime/transcript/done"
+              ],
+              "title": "Thread/realtime/transcript/doneNotificationMethod",
+              "type": "string"
+            },
+            "params": {
+              "$ref": "#/definitions/v2/ThreadRealtimeTranscriptDoneNotification"
+            }
+          },
+          "required": [
+            "method",
+            "params"
+          ],
+          "title": "Thread/realtime/transcript/doneNotification",
           "type": "object"
         },
         {
@@ -10718,6 +10738,13 @@
         ],
         "type": "string"
       },
+      "RealtimeOutputModality": {
+        "enum": [
+          "text",
+          "audio"
+        ],
+        "type": "string"
+      },
       "RealtimeVoice": {
         "enum": [
           "alloy",
@@ -14088,14 +14115,38 @@
         "title": "ThreadRealtimeStartedNotification",
         "type": "object"
       },
-      "ThreadRealtimeTranscriptUpdatedNotification": {
+      "ThreadRealtimeTranscriptDeltaNotification": {
         "$schema": "http://json-schema.org/draft-07/schema#",
         "description": "EXPERIMENTAL - flat transcript delta emitted whenever realtime transcript text changes.",
+        "properties": {
+          "delta": {
+            "description": "Live transcript delta from the realtime event.",
+            "type": "string"
+          },
+          "role": {
+            "type": "string"
+          },
+          "threadId": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "delta",
+          "role",
+          "threadId"
+        ],
+        "title": "ThreadRealtimeTranscriptDeltaNotification",
+        "type": "object"
+      },
+      "ThreadRealtimeTranscriptDoneNotification": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "description": "EXPERIMENTAL - final transcript text emitted when realtime completes a transcript part.",
         "properties": {
           "role": {
             "type": "string"
           },
           "text": {
+            "description": "Final complete text for the transcript part.",
             "type": "string"
           },
           "threadId": {
@@ -14107,7 +14158,7 @@
           "text",
           "threadId"
         ],
-        "title": "ThreadRealtimeTranscriptUpdatedNotification",
+        "title": "ThreadRealtimeTranscriptDoneNotification",
         "type": "object"
       },
       "ThreadResumeParams": {