Notes
workers_dev switches off the moment you add a route
Adding a custom domain to a Cloudflare Worker silently removes its workers.dev URL unless you keep it on by hand.
When this site got its domain, wrangler.jsonc gained a routes entry with custom_domain: true.
Wrangler reacts to that by defaulting workers_dev to false: the portfolio.<account>.workers.dev
address stops serving on the next deploy.
That default is reasonable for a product and wrong for a migration. The old address was the only
fallback while DNS and the certificate were still being confirmed. The fix is one explicit line,
"workers_dev": true, with a comment saying when to flip it back.
The lesson is about defaults that change when a neighbouring setting appears. Read the configuration reference for the field you did not touch, not only for the one you added.