I've been tinkering with the idea of writing a service agent that detects when my Garmin GPS watch is connected to my desktop (where / how I charge it) and automatically pulls down any new activities to store locally as a backup.

Starting around 2012... I used to scrape my activities off of the Garmin Connect website, I eventually got tired of the manual nature of this process and also having to keep up with changes they made to their site. After that, I used something called, I believe, Tapatirik, for a while, to automatically sync them to a Dropbox account. But, it wasn't flaky sometimes, so I eventually gave up entirely and just turned on the sync to Strava option. But that also has spurious failures that are annoying to deal with. And on and on it goes...

Frustrating is one word for it. I'm at a point where I find it to be completely anti-consumer.

GoldenCheetah can do at least some of what you want. https://www.goldencheetah.org/

Thanks for that!

It's not as automatic, but Garmin BaseCamp does let you pull your activities from the watch. I believe it has an option to transfer every time it's open and a device is plugged in, but it doesn't run in the background.

I think working at a crypto startup has changed my life because I see stuff we store about our clients as a total liability...

Based on my experience with their invented proprietary "language" based on Java (with a busted barely-working toolchain) I'm not confident that a lot of thought has gone into doing things sustainably. It has the feeling of being held together with tape and bubblegum wrappers; that the native device and SDKs are a burden to be overcome rather than an empowering interface. I wasn't surprised that they went down during Jim Walmsley's solo Hardrock 100 FKT. I am shocked (but not exactly surprised) that they are still down 24 hours later. I loved the idea of ConnectIQ, and really really wanted them to succeed, but the crippled $500 watch on my wrist will almost certainly be replaced by another brand when its time comes.

This only affects viewing the activities on Garmin Connect. You can view them on the watch just fine, and you can use Garmin BaseCamp on a computer to download the GPX files.

I have a much older version of Fenix (v3) and I can see my activities even from the last year. In Fenix 3 it's in History->Activities menu of the watch.