Request body for PUT /api/mcp/per-user-headers/flows/{id}. The flow row identifies the (mode, identity, mcp_client) triple, so the caller carries only the values. Extra keys not in the live per_user_header_keys schema are dropped server-side.
per_user_header_keys
@type t() :: %ExBifrost.Model.McpHeadersSubmitRequest{ headers: %{optional(String.t()) => String.t()} }