Phase 1 backend for the gallery filter bar. Extends scroll/timeline/jump
from a single mutually-exclusive filter to a composable one:
- tag_ids: image must carry ALL of them (one correlated EXISTS per tag —
AND, no row multiplication), replacing the single-tag JOIN.
- artist_id composes with tags; media_type ('image'|'video') narrows by
mime; post_id stays the exclusive post-detail path.
- sort ('newest'|'oldest') flips the effective_date/id cursor comparison
and ordering; the cursor value is unchanged (direction comes from the
request). jump_cursor honors sort too.
- Shared _apply_scope helper applied across scroll/timeline/jump so the
timeline sidebar reflects the filtered set. API _parse_filters parses
tag_id (comma list), artist_id, media, sort.
Tests: multi-tag AND, media filter, sort reversal (service + API);
post_id-excludes-others; single tag_id back-compat.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
bvandeusen
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