How to know the author of HA reboot?

[123 (Taras)]

Refer to the table in the following post:

Work with "Triggered by" in automations

Based on my own testing, this is combination of values that characterize each action: Action id parent_id user_id Physical Not Null Null Null Automation Not Null Not Null Null UI Not Null Null Not Null A more comprehensive list of actions can be found here. If you are saying that your testing shows that Physical and UI produce identical combinations then, unfortunately for you, there’s no available means of distinguishing between the two.

Unless the triggering source was via the UI, the value of user_id is normally null (none).

Also, are you certain that the trigger object produced by a Homeassistant Trigger contains an event property?

trigger.event.context.user_id
        ^^^^^