chore(tags): remove orphaned cluster tag-gaps route + service method

The cluster tag-gap feature's only UI (Explore's TagGapPanel) was removed in the
3-pane rework, leaving the backend that fed it with no caller. Surgical removal:

- drop the POST /api/images/cluster/tag-gaps route (cluster_tag_gaps)
- drop BulkTagService.tag_gaps (+ the now-unused `import math`)
- drop the tag_gaps tests (test_bulk_tag_service, test_api_bulk_tags)

BulkTagService's common_tags / bulk_add / bulk_remove stay — they still back the
gallery bulk editor. Pure deletion, no behaviour change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/api/tags.py

@@ -320,27 +320,6 @@ async def common_tags():
     return jsonify({"tags": tags})
 
 
-@tags_bp.route("/images/cluster/tag-gaps", methods=["POST"])
-async def cluster_tag_gaps():
-    """Cluster-consensus tag gaps for a visual neighbour set (#94 Explore):
-    tags on >= threshold of the images but not all. Each gap carries the
-    laggard image ids (minus rejections) for apply-to-cluster."""
-    body = await request.get_json()
-    ids, err = _parse_bulk_ids(body)
-    if err:
-        return err
-    try:
-        threshold = float(body.get("threshold", 0.6))
-    except (TypeError, ValueError):
-        threshold = 0.6
-    threshold = min(1.0, max(0.0, threshold))
-    async with get_session() as session:
-        gaps = await BulkTagService(session).tag_gaps(ids, threshold)
-    return jsonify(
-        {"gaps": gaps, "total": len(set(ids)), "threshold": threshold}
-    )
-
-
 @tags_bp.route("/images/bulk/tags", methods=["POST"])
 async def bulk_add_tag():
     body = await request.get_json()

backend/app/services/bulk_tag_service.py

@@ -1,7 +1,5 @@
 """Bulk tag operations over a set of images (Core, set-based, atomic)."""
 
-import math
-
 from sqlalchemy import and_, func, select
 from sqlalchemy.dialects.postgresql import insert as pg_insert
 from sqlalchemy.ext.asyncio import AsyncSession
@@ -15,85 +13,6 @@ class BulkTagService:
     def __init__(self, session: AsyncSession):
         self.session = session
 
-    async def tag_gaps(
-        self, image_ids: list[int], threshold: float
-    ) -> list[dict]:
-        """Cluster-consensus tag gaps (#94 Explore): tags applied to at least
-        `threshold` fraction of the image set but NOT all of it — the
-        "7 of these 10 share Hatsune Miku; these 3 don't" signal.
-
-        For each gap, `missing_image_ids` are the set members that LACK the tag
-        and have NOT rejected it (TagSuggestionRejection) — so apply-to-cluster
-        never re-proposes a tag a neighbor explicitly dismissed. A tag on every
-        image is "common", not a gap; a tag on fewer than 2 isn't consensus.
-        """
-        ids = list({int(i) for i in image_ids})
-        if len(ids) < 2:
-            return []
-        n = len(ids)
-        min_present = max(2, math.ceil(threshold * n))
-        if min_present >= n:
-            return []  # threshold so high only a 100%-common tag could qualify
-
-        cnt = func.count(func.distinct(image_tag.c.image_record_id))
-        gap_rows = (
-            await self.session.execute(
-                select(Tag.id, Tag.name, Tag.kind)
-                .join(image_tag, image_tag.c.tag_id == Tag.id)
-                .where(image_tag.c.image_record_id.in_(ids))
-                .group_by(Tag.id, Tag.name, Tag.kind)
-                .having(and_(cnt >= min_present, cnt < n))
-                .order_by(cnt.desc(), Tag.name.asc())
-            )
-        ).all()
-        if not gap_rows:
-            return []
-        gap_ids = [r.id for r in gap_rows]
-
-        present: dict[int, set[int]] = {}
-        for tid, iid in (
-            await self.session.execute(
-                select(image_tag.c.tag_id, image_tag.c.image_record_id).where(
-                    image_tag.c.tag_id.in_(gap_ids),
-                    image_tag.c.image_record_id.in_(ids),
-                )
-            )
-        ).all():
-            present.setdefault(tid, set()).add(iid)
-
-        rejected: dict[int, set[int]] = {}
-        for tid, iid in (
-            await self.session.execute(
-                select(
-                    TagSuggestionRejection.tag_id,
-                    TagSuggestionRejection.image_record_id,
-                ).where(
-                    TagSuggestionRejection.tag_id.in_(gap_ids),
-                    TagSuggestionRejection.image_record_id.in_(ids),
-                )
-            )
-        ).all():
-            rejected.setdefault(tid, set()).add(iid)
-
-        id_set = set(ids)
-        gaps = []
-        for r in gap_rows:
-            have = present.get(r.id, set())
-            missing = id_set - have - rejected.get(r.id, set())
-            if not missing:
-                continue  # every laggard rejected it — nothing to apply
-            gaps.append(
-                {
-                    "tag_id": r.id,
-                    "name": r.name,
-                    "kind": r.kind.value if hasattr(r.kind, "value") else str(r.kind),
-                    "present_count": len(have),
-                    "total": n,
-                    "missing_image_ids": sorted(missing),
-                }
-            )
-        return gaps
-
     async def common_tags(self, image_ids: list[int]) -> list[dict]:
         """Tags present on EVERY image in image_ids."""
         if not image_ids:

tests/test_api_bulk_tags.py

@@ -87,42 +87,3 @@ async def test_bulk_remove_route_requires_ids(client):
         "/api/images/bulk/tags/remove", json={"tag_id": 1}
     )
     assert resp.status_code == 400
-
-
-@pytest.mark.asyncio
-async def test_cluster_tag_gaps_requires_list(client):
-    resp = await client.post("/api/images/cluster/tag-gaps", json={})
-    assert resp.status_code == 400
-
-
-@pytest.mark.asyncio
-async def test_cluster_tag_gaps_route_reports_gap(client, db):
-    from backend.app.models import ImageRecord, TagKind
-    from backend.app.services.tag_service import TagService
-
-    tags = TagService(db)
-    gap = await tags.find_or_create("GapRoute", TagKind.general)
-    imgs = []
-    for i in range(4):
-        rec = ImageRecord(
-            path=f"/tmp/gaproute_{i}.png", sha256=f"g{i:063d}",
-            size_bytes=1, mime="image/png", origin="uploaded",
-        )
-        db.add(rec)
-        await db.flush()
-        imgs.append(rec.id)
-    for i in imgs[:3]:
-        await tags.add_to_image(i, gap.id)   # on 3/4 → a gap at 0.6
-    await db.commit()
-
-    resp = await client.post(
-        "/api/images/cluster/tag-gaps",
-        json={"image_ids": imgs, "threshold": 0.6},
-    )
-    assert resp.status_code == 200
-    body = await resp.get_json()
-    assert body["total"] == 4
-    assert body["threshold"] == 0.6
-    g = next(x for x in body["gaps"] if x["tag_id"] == gap.id)
-    assert g["present_count"] == 3
-    assert g["missing_image_ids"] == [imgs[3]]

tests/test_bulk_tag_service.py

@@ -120,59 +120,3 @@ async def test_bulk_remove_rejection_is_idempotent(db):
     # Second remove: nothing to delete, rejection already present, no error.
     removed = await svc.bulk_remove([i1], tag.id)
     assert removed == 0
-
-
-@pytest.mark.asyncio
-async def test_tag_gaps_finds_consensus_excludes_common(db):
-    tags = TagService(db)
-    gap = await tags.find_or_create("Miku", TagKind.character)
-    common = await tags.find_or_create("Solo", TagKind.general)
-    imgs = [await _img(db) for _ in range(5)]
-    for i in imgs:
-        await tags.add_to_image(i, common.id)   # on all 5 → not a gap
-    for i in imgs[:4]:
-        await tags.add_to_image(i, gap.id)       # on 4/5 → a gap
-    svc = BulkTagService(db)
-    gaps = await svc.tag_gaps(imgs, threshold=0.6)
-    assert [g["tag_id"] for g in gaps] == [gap.id]   # the common tag is excluded
-    g = gaps[0]
-    assert g["present_count"] == 4
-    assert g["total"] == 5
-    assert g["missing_image_ids"] == [imgs[4]]
-
-
-@pytest.mark.asyncio
-async def test_tag_gaps_excludes_rejected_laggard(db):
-    tags = TagService(db)
-    gap = await tags.find_or_create("Rin", TagKind.character)
-    imgs = [await _img(db) for _ in range(6)]
-    for i in imgs[:4]:
-        await tags.add_to_image(i, gap.id)       # on 4/6 (min_present=ceil(3.6)=4)
-    # imgs[4], imgs[5] lack it; imgs[4] explicitly rejected it.
-    db.add(TagSuggestionRejection(image_record_id=imgs[4], tag_id=gap.id))
-    await db.flush()
-    svc = BulkTagService(db)
-    gaps = await svc.tag_gaps(imgs, threshold=0.6)
-    g = next(x for x in gaps if x["tag_id"] == gap.id)
-    assert g["missing_image_ids"] == [imgs[5]]   # rejected laggard excluded
-
-
-@pytest.mark.asyncio
-async def test_tag_gaps_drops_tag_when_all_laggards_rejected(db):
-    tags = TagService(db)
-    gap = await tags.find_or_create("Len", TagKind.character)
-    imgs = [await _img(db) for _ in range(5)]
-    for i in imgs[:4]:
-        await tags.add_to_image(i, gap.id)       # on 4/5, sole laggard imgs[4]
-    db.add(TagSuggestionRejection(image_record_id=imgs[4], tag_id=gap.id))
-    await db.flush()
-    svc = BulkTagService(db)
-    gaps = await svc.tag_gaps(imgs, threshold=0.6)
-    assert all(g["tag_id"] != gap.id for g in gaps)  # nothing to apply → dropped
-
-
-@pytest.mark.asyncio
-async def test_tag_gaps_needs_at_least_two_images(db):
-    svc = BulkTagService(db)
-    assert await svc.tag_gaps([], 0.6) == []
-    assert await svc.tag_gaps([await _img(db)], 0.6) == []