Temporal has a namespace policy bypass allowing requests to be authorized for incorrect contexts

When frontend.enableExecuteMultiOperation is enabled, the server can apply namespace-scoped validation and feature gates for the embedded StartWorkflowExecutionRequest using its Namespace field rather than the outer, authorized ExecuteMultiOperationRequest.Namespace. This allows a caller authorized for one namespace to bypass that namespace's limits/policies by setting the embedded start request's namespace to a different namespace. The workflow is still created in the outer (authorized) namespace; only validation/gating is performed under the wrong namespace context. This issue affects Temporal: from 1.24.0 through 1.29.1. Fixed in 1.27.4, 1.28.2, 1.29.2.