Owning the walk lets an operator gauge "is this source worth a backfill?" before
arming one. ingest_core.Ingester.preview walks the first few feed pages and
counts media NOT already in the seen/dead ledgers, downloading nothing
(read-only). download_backends.preview_source resolves the campaign id + runs it
(native-only, mirrors verify_source_credential / run_download); POST
/api/sources/{id}/preview returns {total_new, posts_scanned, has_more, sample[]}
(409 on auth/drift/unresolvable, 400 for gallery-dl platforms). PatreonClient
gains post_meta(post) for the sample's title/date.
UI: a Patreon-only Preview button (mdi-eye-outline) on SourceRow + SourceCard
opens PreviewDialog — self-fetches with loading / error / empty / result states
and a "Start backfill" shortcut. Store action previewSource.
Tests: preview counts new media without downloading + samples only posts with
new items; page_limit caps the walk + flags has_more.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
bvandeusen
e82c2ee57b