The client, not the app, now drives the transport; events are delivered
asynchronously, per ADR 0001.
- ChatClient owns Arc<Mutex<Core>> + a worker thread.
- The worker select!s over the inbound and shutdown channels; Drop joins it.
Outbound runs on the caller's thread.
- A single Transport (DeliveryService + inbound()) owns both directions of the
boundary, so the client takes one transport rather than a (delivery, inbound)
pair. InProcessDelivery::new, CDelivery, and chat-cli's transports implement it.
- FFI replaces client_receive with client_push_inbound + client_poll_events.
- chat-cli drains Receiver<Event>; inbound and event channels are both crossbeam.
- Corrects ADR 0001's inbound sequence to push — the worker parks on select!,
it never polls.
Replace the direct use of `conversations::Context` with `client::ChatClient`,
which is the intended public API for library consumers.
Remove `MessageEnvelope` and the username-keyed session model. The envelope
was never part of the wire protocol — sender identity was only tracked in the
CLI's local state. Chats are now keyed by conversation ID; add `/nickname` as
the user-facing replacement for named sessions.
Add a logos-delivery (Waku) transport alongside the existing file transport.
The active transport is selected at compile time: set `LOGOS_DELIVERY_LIB_DIR`
to link liblogosdelivery, otherwise the file transport is used.
Add logos-delivery as a Nix flake input and expose `.#logos-delivery` so the
library can be built with `nix build` and referenced by `LOGOS_DELIVERY_LIB_DIR`.
CI: rename `c-ffi-smoketest` to `smoketest`; add logos-delivery build step
and a `--smoketest` invocation of chat-cli to verify startup.
