An instance published behind an access list or Cloudflare Zero Trust gets
an HTML login or error page in place of JSON once that session expires.
`resp.json()` then throws "Unexpected token '<', "<!DOCTYPE "...", and the
repeater panes printed that at the user. Diagnosed on the production
server 2026-09-08: the origin had answered a clean 504 JSON ("No reply
from repeater within 10s") and nginx passed it through untouched, so the
HTML could only have come from in front of it.
New window.fetchJson() (fetch-utils.js, loaded from _head_i18n.html so all
eight entry points get it) returns the parsed body — `data.success` and
`data.error` checks are unchanged — and reports anything else in the same
shape the API uses: {success:false, error, http_status, non_json|offline}.
A 401/403 with a non-JSON body is named as an expired login, since that is
the case the user can act on; an error the API sent as JSON keeps its own
message. 88 call sites converted; those that deliberately inspect the
response (resp.ok/status, blob, uploads) still use fetch directly.
Also stops three catch blocks in the repeater panes from rendering the raw
exception text.
Verified in a browser: normal calls unchanged, an HTML answer comes back
as a readable sentence, a refused connection as a network error, and all
seven pages load with no console errors.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
