Users can now list available agents with !agent and select one by
number. Selection persists in user metadata (selected_agent_id). If the
current room has no agent binding yet, selecting an agent binds it
immediately so the user can start messaging without !new.
Also updates the dispatcher test to reflect that real-mode platform is
now RoutedPlatformClient, not a bare RealPlatformClient.
Upstream AgentApi responses can return attachment objects that don't
implement the Attachment dataclass. _to_core_attachments coerces them
via duck-typing so OutgoingMessage always carries typed Attachment
instances regardless of the upstream response shape.
Instead of calling a /reset endpoint on platform-agent, !reset now
generates a new thread_id (platform_chat_id) for the room. The old
WebSocket connection is closed and the next message creates a fresh
context automatically. No platform changes required.
Add step-by-step setup for running Matrix surface with real platform-agent,
document all available commands, and clearly list what works vs what is
blocked (StateBackend cross-chat load, hardcoded tokens, missing /reset,
no file upload API).
AgentApiWrapper._build_ws_url was building /v1/agent_ws/{chat_id}/
which does not exist in platform-agent. Fixed to /agent_ws/?thread_id={chat_id}
to match the actual endpoint and query-param isolation scheme.
Also simplify Matrix MVP settings handlers to MVP_UNAVAILABLE stubs
and add handle_unknown_command for unregistered !commands.
