RelayAdapter.on_interrupt(session_key, chat_id) bridges a connector-delivered
mid-turn /stop into the existing interrupt_session_activity path, setting the
per-session _active_sessions Event and clearing typing — cancelling exactly the
targeted session's turn without touching siblings (mirrors test_stop_thread_
sibling isolation). Transport.send_interrupt carries the gateway-side egress to
the connector for socket-owner routing.
Phase 1, Task 1.4 of the gateway-relay plan.
Defines RelayTransport (lifecycle/handshake/inbound/outbound/interrupt) as the
gateway<->connector wire contract; RelayAdapter.connect now registers an inbound
handler that bridges connector-delivered MessageEvents into handle_message.
Adds an in-memory StubConnector under tests/ and an E2E round-trip proving:
connect registers the handler, inbound events reach the adapter, guild_id drives
build_session_key isolation (two guilds -> two keys; same guild/channel/user ->
one), outbound send round-trips, get_chat_info is proxied.
Phase 1, Task 1.2 of the gateway-relay plan.
One BasePlatformAdapter subclass that reads its capability profile from a
CapabilityDescriptor: MAX_MESSAGE_LENGTH attribute, message_len_fn (table-driven
by len_unit: chars=len, utf16=Telegram-style code units), supports_draft_streaming.
Implements the four abstract methods (connect/disconnect/send/get_chat_info) by
delegating to an injected RelayTransport (full protocol lands in Task 1.2). Adds
Platform.RELAY enum member. No per-platform gateway code.
Phase 1, Task 1.1 of the gateway-relay plan.
