Use echo speaks
While I am going to continue to investigate alternatives I am happy to say my crude workaround of doing initialize()
plus playTrack(silent mp3)
every 4 minutes is working tolerably well. I may yet have a connectivity failure and Hub meltdown as @Jost has described but it has not happened yet.
I have never heard bloop before playback starts.
A couple of times, days apart, I heard a bloop for no reason. I didn't check the logs but that must mean that somehow, the message didn't get through and the speaker fell asleep. Maybe the keep-alive needs a timing adjustment or added delay.
I'll also refine the rules so the keep-alive action plays at minimal volume in case a bloop gets through somehow, and explicitly set volume in notifications.
This is ridiculous, but at least it's working.
I also updated the title of this thread to reflect where it went, not how it started.
Following exactly the documentation (App Configuration - Echo Speaks Documentation),,,
Everytime I try "Step 7" of the "Server Configuration" I just get a "404" Page,
As I already said:
"Alexa TTS by Hubitat is very ... cumbersome"