Drat; I’ve been meaning to try the Smile AppleScript editor, but waited too long, and it’s incompatible with modern macOS - HOWEVER:

I trashed the /Applications/Smile directory (no uninstaller in there), and then re-opened Script Editor to get back to work - but it hung; never completed startup and showed no error messages. Strange.

After a bit of debugging, I recalled that when I’d installed Smile - since I luckily already had Apple’s built-in Script Editor app open - the Installer told me it had to quit that first. Interesting - and seemed maybe relevant now.

So I started hunting for evidence of just what had been installed - likely something conflicting with Script Editor (at least).

/var/log/install.log did have some info, and so did /private/var/db/receipts - which led to the solution (in my case anyway), which was also deleting these directories:

/Library/Application Support/Smile

After which, Script Editor was able to finish startup - and even showed the unsaved script that I’d been working on. Nice.