Introduce core/ — a Rust crate owning the wire protocol (Message codec,
SSE client, reconnect/backoff, send) behind a 4-method seam exported via
UniFFI: Engine::new / start(handler) / send / stop. This is the single
sync engine meant to back all clients; desktop links it directly, iOS
binds an .xcframework, Android will bind an .aar. RTC mesh + the signal
envelope are deliberately out of scope for v1 (SSE-only).
Verified end-to-end against the live server: examples/roundtrip.rs has a
subscriber engine receive a message published by a sender engine.
iOS now links it: TetherStore drops TetherKit's TetherClient/SSEClient/
Message and drives tethercore.Engine instead (RoomIdentity still from
TetherKit via selective import to avoid the Message name clash). The app
builds and links the Rust staticlib for device.
Artifacts (xcframework, Swift bindings) are generated by core/build-ios.sh
and git-ignored; commit source + script, not the ~80MB static libs.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Patrick Ecord
2c375632a5
