Thanks! I did try manual installs but it still wasn’t working. On reflection I realized I was having trouble with the “store installer.” Installing from an installer is a new feature since I did my last full system install, and reading the notes it says it relies on OBS and may take a few days after a new release comes out to get all the necessary repos in order.
Fortunately they also listed a path to the actual, old school storeman installation files (i.e. not the ‘installer’.) That worked and I was able to install Rockpool and a range of other tools with all dependencies. My Pebble is now up and running with the Xperia 10.
Leaving this issue here in case someone else has the same problem. I found the Storeman Installer at Storeman Installer | OpenRepos.net — Community Repository System
And the original files via State of Repository 4.3.0.12_armv7hl for home:mentaljam / harbour-storeman-sfos3.3 - SailfishOS Open Build Service - I followed the links and downloaded the armv7hl rpm from Index of /obs/home:/mentaljam/4.3.0.12_armv7hl/armv7hl
Thank you for the help, @Seven.of.nine and @Inte !