Add request permissions tool (#13092)

Adds a built-in `request_permissions` tool and wires it through the
Codex core, protocol, and app-server layers so a running turn can ask
the client for additional permissions instead of relying on a static
session policy.

The new flow emits a `RequestPermissions` event from core, tracks the
pending request by call ID, forwards it through app-server v2 as an
`item/permissions/requestApproval` request, and resumes the tool call
once the client returns an approved subset of the requested permission
profile.

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -5033,6 +5033,42 @@
           "title": "ExecApprovalRequestEventMsg",
           "type": "object"
         },
+        {
+          "properties": {
+            "call_id": {
+              "description": "Responses API call id for the associated tool call, if available.",
+              "type": "string"
+            },
+            "permissions": {
+              "$ref": "#/definitions/PermissionProfile"
+            },
+            "reason": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
+            "turn_id": {
+              "default": "",
+              "description": "Turn ID that this request belongs to. Uses `#[serde(default)]` for backwards compatibility.",
+              "type": "string"
+            },
+            "type": {
+              "enum": [
+                "request_permissions"
+              ],
+              "title": "RequestPermissionsEventMsgType",
+              "type": "string"
+            }
+          },
+          "required": [
+            "call_id",
+            "permissions",
+            "type"
+          ],
+          "title": "RequestPermissionsEventMsg",
+          "type": "object"
+        },
         {
           "properties": {
             "call_id": {