Mention legacy exec permission flow in prompt guidance

Include with_additional_permissions guidance when either exec permission approvals or the request-permissions tool path is enabled, and add a permissions-message regression test for the legacy exec approvals flow.

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

codex-rs/core/src/context_manager/updates/developer_update_fragments.rs

@@ -100,7 +100,10 @@ impl TurnContextDiffFragment for PermissionsUpdateFragment {
                 &turn_context.cwd,
                 turn_context
                     .features
-                    .enabled(Feature::RequestPermissionsTool),
+                    .enabled(Feature::ExecPermissionApprovals)
+                    || turn_context
+                        .features
+                        .enabled(Feature::RequestPermissionsTool),
             ),
         })
     }