When send_message is invoked from the agent's worker thread (a different
event loop than the gateway's), awaiting the WeCom adapter directly can hang
because the adapter enqueues onto the gateway loop. Dispatch via
run_coroutine_threadsafe onto the gateway loop when the caller loop differs,
with caller-cancellation shielded so an already-enqueued send is not cancelled
mid-flight (which would otherwise cause a false-failure retry -> duplicate).
Recognizes WeCom native chat IDs as explicit send targets and whitelists WeCom
for media delivery. Part of the async queue design this branch introduces.
wansui