[codex-analytics] add protocol-native turn timestamps (#16638)

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[//]: # (BEGIN SAPLING FOOTER)
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with [ReviewStack](https://reviewstack.dev/openai/codex/pull/16638).
* #16870
* #16706
* #16659
* #16641
* #16640
* __->__ #16638

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

@@ -14329,6 +14329,22 @@
       },
       "Turn": {
         "properties": {
+          "completedAt": {
+            "description": "Unix timestamp (in seconds) when the turn completed.",
+            "format": "int64",
+            "type": [
+              "integer",
+              "null"
+            ]
+          },
+          "durationMs": {
+            "description": "Duration between turn start and completion in milliseconds, if known.",
+            "format": "int64",
+            "type": [
+              "integer",
+              "null"
+            ]
+          },
           "error": {
             "anyOf": [
               {
@@ -14350,6 +14366,14 @@
             },
             "type": "array"
           },
+          "startedAt": {
+            "description": "Unix timestamp (in seconds) when the turn started.",
+            "format": "int64",
+            "type": [
+              "integer",
+              "null"
+            ]
+          },
           "status": {
             "$ref": "#/definitions/v2/TurnStatus"
           }