feat: opt-in auto-tag on download, marked as AI (P13c-2)

[blokzdev]

What & why

Follow-up to P13c: optionally apply LLM tags to new downloads in the background, opt-in (default off). Because tags are user-curated (they drive facets), auto-applied tags are marked as AI — provenance + a ✦ marker, deletable — rather than silently mixed in (the apply model you chose). Mirrors the P13a-2/P13b-3 queue pattern + reuses all of P13c's tag logic.

Changes

• Schema v12→v13: MediaTags.source (default 'user'); addTagToItem(…, {source}) — insertOrIgnore keeps an existing link's source, so a user tag is never demoted to 'ai'; watchAiTagNamesForItem + aiTagNamesForItemProvider. The v13 migration guards the addColumn with a table-existence check (mirrors the existing v8 guard-add pattern) so partial older migration-test DBs don't break.
• Settings: autoTagOnDownload (default off) + setter; _AutoTagTile in the generation card.
• Queue (_persistCompleted, after the auto-OCR block): a pure autoTagDecision (skip/needsModel/tag) gates per item; build source from title + description/transcript/ocrText → buildTagPrompt → generate → parseTagSuggestions(exclude: applied) → addTagToItem(source: 'ai'); tagCount/tagNeedsModel → an ai inbox entry ("N tags added") or a "finish setup" nudge.
• Marking: editor + item-detail tag chips show auto_awesome_outlined on AI-sourced tags; AI tags still appear as normal search facets (the benefit).

Tests

dart format clean · flutter analyze No issues · flutter test 824 passed — autoTagDecision, repo provenance (only-AI set; user not demoted), the v12→v13 migration, settings round-trip, and queue cases (applied as 'ai' + an ai entry; default-off no-op).

Honest notes

• Owed APK spot-check (VERIFICATION → P13c-2): real download → sensible AI-marked tags applied + an inbox entry, offline; they appear as facets; deleting an AI tag works; default-off / no-model behave. Native generation can't be CI-tested.
• A real regression caught before merge: the new aiTagNamesForItemProvider (a live Drift watch stream) made _TagsRow/_TagsEditor leak a query Timer in widget tests that don't stub it → 15 item-detail/editor tests failed. I added the finite Stream.value({}) override to every affected ProviderScope (the same pattern those tests already use for tagsForItemProvider). Worth flagging because a | tail pipe initially masked the failing exit code — I re-ran without the pipe to confirm.
• The defensive table-guard in the v13 migration is production-harmless (media_tags always exists) and consistent with the codebase's existing addColumnIfMissing guard for schema drift.
• Deferred (BACKLOG): a library "hide/filter AI tags" facet and promoting an AI tag to 'user' on manual re-add.

This closes the auto-tag follow-up. Next up: P13d — local GraphRAG "Ask your library" (the flagship).

https://claude.ai/code/session_013JoYmLCosYt5tQ8qwdbL1T

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