_do_ensure only tried the batch API when _batch_api_works was True,
but after removing the search-time prefetch (where the probe used
to run), _batch_api_works stayed None forever. Gelbooru's only
viable path IS the batch API (its post-view HTML has no tag links),
so clicks on Gelbooru posts produced zero categories.
Fix: _do_ensure now tries the batch API when _batch_api_works is
not False (i.e., both True and None). When None, the call doubles
as an inline probe: if the batch produced categories, save True;
if nothing useful came back, save False and fall to HTML.
This is simpler than the old prefetch_batch probe because it runs
on ONE post at a time — no batch/HTML mixing concerns, no "single
path per invocation" rule. The probe result is persisted to DB so
it only fires once per site ever.
Dispatch matrix in _do_ensure:
_batch_api_works True + auth → batch API (Gelbooru proper)
_batch_api_works None + auth → batch as probe → True or False
_batch_api_works False → HTML scrape (Rule34)
no auth → HTML scrape (Safebooru.org)
transient error → stays None, retry next click
Verified all three sites from clean cache: Gelbooru 55/56+49/50
(batch), Rule34 40/40+38/38 (HTML), Safebooru.org 47/47+47/47
(HTML).
pax
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