@powerkiki thanks for the suggestion. Since posting, I did figure out that (not surprisingly) the fault is in my code somewhere, not the framework’s, by creating a new skeleton app and fiddling with composer development-(enable|disable). Again, no surprise, but one always has to rule that out.
I believe I started with the skeleton, but it was 4+ years ago; it was ZF2, became ZF3, became Laminas, and has diverged vastly from the skeleton. Either I must have removed those composer scripts from my composer.json or else they didn’t exist back then.
UPDATE:
composer require laminas/laminas-development-mode and the rest is simple.
Thanks!