The danbooru and e621 API clients store tag_categories with
Capitalized keys ("Artist", "Character", "Copyright", "General",
"Meta", "Species") — that's the convention info_panel and
preview_pane already iterate against. render_filename_template was
looking up lowercase keys, so every category token rendered empty
even on Danbooru posts where the data was right there. Templates
like "%id%_%character%" silently collapsed back to "{id}.{ext}".
Fix: look up the Capitalized form, with a fallback chain (exact ->
.lower() -> .capitalize()) so future drift between API clients in
either direction won't silently break templates again.
Verified against a real Danbooru save in the user's library: post
11122211 with tag_categories containing Artist=["yun_ze"],
Character=["mon3tr_(arknights)"], etc. now renders
"%id%_%character%" -> "11122211_mon3tr_(arknights).jpg" instead of
"11122211.jpg".
pax
f0b1fc9052