Elm ports: missing ordering guarantee between inbound and outbound messages

Goal

Design a bidirectional Elm↔JavaScript communication where a command sent through an outgoing port receives an immediate, ordered reply on an incoming port. The application logic assumes that the reply corresponds to the most recent command.

Constraints & Uncertainty

Elm ports intentionally treat the Elm↔JavaScript boundary as asynchronous. The Elm compiler and runtime documentation make no mention of delivery order between messages flowing in opposite directions. Under load, the JavaScript event loop can interleave or reorder messages, potentially causing a reply to arrive before the preceding command is processed.

Because the language offers no built‑in acknowledgment or sequencing primitive, developers must decide whether to rely on application‑level correlation IDs, redesign the interaction as fully asynchronous, or accept the risk of race conditions.

Questions

• Does the Elm runtime provide any hidden guarantees about the relative ordering of messages sent through outgoing ports and those received on incoming ports?
• If no ordering is guaranteed, are there any officially supported patterns or libraries that can enforce a deterministic sequence across the Elm↔JavaScript boundary?
• What are the documented consequences for applications that require synchronous request/response semantics using ports?