Point at can_proceed() for handshake-dependent flags

esphome/core/entity_base.h

@@ -92,6 +92,7 @@ class EntityBase {
   // whenever possible: it is guaranteed and has none of the limitations below. Use this only when
   // the decision can only be made at boot. Must be called before MQTT and the API read the flag:
   // from on_boot at the default priority, or a setup() that runs above setup_priority::AFTER_WIFI.
+  // If the answer comes from a device handshake, hold setup with can_proceed() until it arrives.
   // Calls after setup finishes are undefined behavior: the flag is still written and an error is
   // logged, and from 2027.3.0 the call will be ignored.
   //