Injected full-duplex transport contract for Live providers.

open/2 returns a private handle and asynchronously reports transport state to Owner using the messages below. send/2 may return busy; the session then retains the frame in its bounded ingress queue until a writable message arrives.

{adk_live_transport, Handle, connected} {adk_live_transport, Handle, writable} {adk_live_transport, Handle, {sent, SendRef}} {adk_live_transport, Handle, {frame, Binary}} {adk_live_transport, Handle, {closed, OpaqueReason}}

Implementations must redact credentials, endpoint query strings and provider resumption handles from errors and diagnostic state.