Google Calendar : How to get the list of events when HA starts?

I’m trying to set up the Google calendar integration with the new UI integration.

When an event starts or ends, an automation can be triggered to get the summary, the start/end time and then I can switch on/off the heaters.

in the developper tool I can find one sensor for my calendar with only one event , not all the events currently running

My question is the following:
When HA starts, how can I get the list of events in my calendar to find if one event has already started and I need to switch on the heater (for exemple) or that the event is finished and I need to switch off the heater (because the event finished when HA was down ?

Thanks for your help