Include spawn agent model metadata in app-server items

Add the spawned agent's model and reasoning effort to app-server collab turn items and notifications so turn history matches spawn events.

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

codex-rs/app-server-protocol/schema/json/v2/TurnStartedNotification.json

@@ -488,6 +488,18 @@
         }
       ]
     },
+    "ReasoningEffort": {
+      "description": "See https://platform.openai.com/docs/guides/reasoning?api-mode=responses#get-started-with-reasoning",
+      "enum": [
+        "none",
+        "minimal",
+        "low",
+        "medium",
+        "high",
+        "xhigh"
+      ],
+      "type": "string"
+    },
     "TextElement": {
       "properties": {
         "byteRange": {
@@ -865,6 +877,13 @@
               "description": "Unique identifier for this collab tool call.",
               "type": "string"
             },
+            "model": {
+              "description": "Model requested for the spawned agent, when applicable.",
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "prompt": {
               "description": "Prompt text sent as part of the collab tool call, when available.",
               "type": [
@@ -872,6 +891,17 @@
                 "null"
               ]
             },
+            "reasoningEffort": {
+              "anyOf": [
+                {
+                  "$ref": "#/definitions/ReasoningEffort"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "description": "Reasoning effort requested for the spawned agent, when applicable."
+            },
             "receiverThreadIds": {
               "description": "Thread ID of the receiving agent, when applicable. In case of spawn operation, this corresponds to the newly spawned agent.",
               "items": {