Thank you for the reference, @UserSeventeen. Based on the web page you pointed to, I was able to test the built-in local variables, which appeared in the list of local variables once I added a trigger for my test rule, and used the trigger instead of just "run actions" to cause the rule to fire. The result (of my log action) is:
app:134 2025-01-08 12:58:02.770 info Log test of currentMode: (null); device: (Sunroom east light button); value: (1); text: (Button 1 (On) was pushed); date: (2025-01-08); time: (12:58); now: (12:58)
Note that the %text% variable refers to the trigger, not to the previous action in the rule's action list (which was to set Mode to Day). I'm learning something, and I'm pleased about that, but it doesn't address my original problem, which was to access the information set up by the Hub Information Driver. When I look at that virtual device, under Events and under Current States I see all the right stuff, including currentMode, but I have no idea how to pull that information into a Log action in another rule.
Set up a few local vars in your RM rule, to receive the info we're about to pull from Hub Info driver. Create one action per var, namely "SET VARIABLE" > Device Attribute, and of course select the corresponding attribute you want the value from.
Now that you have captured those values, you can freely reference the %local_var_name_here% in subsequent RM actions.
Ah, I think I get it now! In a rule, I can do "percent-style" references only to local variables (including the "special" ones mentioned in the documentation for rule 5.1, that is, %text%, %value%, and friends), so if I want to refer to a device attribute, I have to first pull that into a local variable. That works! Thanks, @UserSeventeen.
And thank you also, @kahn-hubitat, for reminding me that I could just trigger on the attribute change (in Hub Information Driver) directly. That's not what I'm looking for in this case, but it will be useful for other cases.
I had a rule that used Hubitat Hub Controller to either reboot the hub or "restart the Hubitat application" (from that app's sparse documentation). I'm not totally sure how "restart the Hubitat application" differs from "reboot the hub", but I'd like to switch over to HIDv3 (it appears that Hubitat Hub Controller no longer works correctly in 2.4.0.146 -- my previously fine rule started rebooting my hub every 7-8 minutes).
I see that HIDv3 has a reboot command, but not a "restart" command. Is there something comparable to a restart in HIDv3?