a control plane that relays nothing

The first architecture was a relay. Every message travelled from a worker, through a coordination service, out to whoever was listening. It is the obvious shape, and it has a property that is easy to miss until it is expensive: the coordination service sits on the data path, so its throughput is everyone's throughput and its faults are everyone's faults.

The reversal replaced the data plane with shared memory per room. Each room owns a region and an index; a writer appends directly and updates its own position, with nothing in the middle. The coordination service keeps only what needs to be central, which is who is in which room and whether the backing storage is healthy. No payload bytes pass through it.

The boundary is crossed once, at join time, to hand the worker a descriptor for the shared region, and that hand-over was proven across the container boundary before the design was accepted. After that, readers validate the region's own header instead of asking permission.

The cost was large and it was paid in deleted work. Several planned phases existed only to carry a message relay: framing, fragmentation, flow control, batching, resumption. They were not ported; they stopped being necessary. Documents were rewritten rather than amended, and every settled choice was numbered and recorded so the reasoning survived the rewrite.

What this proves: the team can recognise a design whose cost is structural, reverse it while the code is still small, and pay for abandoning planned work instead of defending it.