refactor(ml): remove the dead per-tag centroid subsystem (#1189)

The v2 pivot replaced per-tag SigLIP centroids with learned heads + CCIP.
Centroids were still recomputed (on every tag merge + a daily beat) but NOTHING
read them — suggestions come from heads+CCIP and apply_allowlist_tags applies
via Camie predictions, not centroids. Pure dead wiring; remove it.

Removed: CentroidService, recompute_centroid/recompute_centroids tasks, the
daily beat, POST /api/ml/recompute-centroids, the recompute-on-merge trigger,
the tag_reference_embedding table + model, the centroid_similarity_threshold +
min_reference_images settings (migration 0066), the CentroidRecomputeCard +
its store action + MaintenancePanel tile, and the centroid slider in
MLThresholdSliders. _keep_as_alias drops its vestigial has-centroid branch (the
allowlist branch already covers "could re-emit"); tag merge no longer clears a
table that no longer exists.

NOT touched (still live, parallel to heads): the Camie tagger, ImagePrediction,
and the allowlist bulk-apply — accepting a suggestion still allowlists + applies
it across the library. The tag-eval "centroid" baseline metric is unrelated
(in-memory) and stays. (image_record.centroid_scores JSON column also remains —
separate legacy field, its own micro-cleanup.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

tests/test_api_ml_admin.py

@@ -107,11 +107,9 @@ async def test_video_min_tag_frames_above_max_rejected(client):
 
 
 @pytest.mark.asyncio
-async def test_backfill_and_recompute_trigger(client):
+async def test_backfill_trigger(client):
     r1 = await client.post("/api/ml/backfill")
     assert r1.status_code == 202
-    r2 = await client.post("/api/ml/recompute-centroids")
-    assert r2.status_code == 202
 
 
 @pytest.mark.asyncio

tests/test_migration_0003.py

@@ -6,7 +6,6 @@ from backend.app.models import (
     MLSettings,
     TagAlias,
     TagAllowlist,
-    TagReferenceEmbedding,
     TagSuggestionRejection,
 )
 
@@ -16,7 +15,6 @@ def test_new_tables_registered():
         "tag_allowlist",
         "tag_suggestion_rejection",
         "tag_alias",
-        "tag_reference_embedding",
         "ml_settings",
     }
     assert expected.issubset(Base.metadata.tables.keys())
@@ -42,12 +40,6 @@ def test_ml_settings_singleton_constraint():
     assert "ck_ml_settings_singleton" in names
 
 
-def test_tag_reference_embedding_has_vector():
-    cols = {c.name for c in TagReferenceEmbedding.__table__.columns}
-    assert "embedding" in cols
-    assert "reference_count" in cols
-
-
 def test_tag_allowlist_confidence_check():
     names = {c.name for c in TagAllowlist.__table__.constraints}
     assert "ck_tag_allowlist_confidence_range" in names

tests/test_ml_artist_retired.py

@@ -8,12 +8,6 @@ def test_artist_not_surfaced():
     assert "artist" not in SURFACED_CATEGORIES
 
 
-def test_artist_not_centroid_eligible():
-    from backend.app.models import TagKind
-    from backend.app.services.ml.centroids import ELIGIBLE_KINDS
-    assert TagKind.artist not in ELIGIBLE_KINDS
-
-
 def test_artist_not_head_eligible():
     # Tagging-v2: suggestions come from heads, and heads are only trained for
     # general/character concepts — so 'artist' (and any other kind) can't surface.

tests/test_ml_centroids.py

@@ -1,112 +0,0 @@
-import numpy as np
-import pytest
-
-from backend.app.models import ImageRecord, TagKind
-from backend.app.models.tag import image_tag
-from backend.app.services.ml.centroids import CentroidService
-from backend.app.services.tag_service import TagService
-
-pytestmark = pytest.mark.integration
-
-
-def _img(sha: str, embedding: list[float] | None) -> ImageRecord:
-    return ImageRecord(
-        path=f"/images/{sha}.jpg",
-        sha256=sha,
-        size_bytes=1,
-        mime="image/jpeg",
-        width=1,
-        height=1,
-        origin="imported_filesystem",
-        integrity_status="unknown",
-        siglip_embedding=embedding,
-    )
-
-
-async def _attach(db, image_id: int, tag_id: int):
-    await db.execute(
-        image_tag.insert().values(
-            image_record_id=image_id, tag_id=tag_id, source="manual"
-        )
-    )
-
-
-@pytest.mark.asyncio
-async def test_recompute_skips_too_few_members(db):
-    tags = TagService(db)
-    tag = await tags.find_or_create("Lonely", TagKind.character)
-    img = _img("a" * 64, [0.1] * 1152)
-    db.add(img)
-    await db.flush()
-    await _attach(db, img.id, tag.id)
-
-    svc = CentroidService(db)
-    assert await svc.recompute_for_tag(tag.id) is False
-
-
-@pytest.mark.asyncio
-async def test_recompute_writes_centroid(db):
-    tags = TagService(db)
-    tag = await tags.find_or_create("Popular", TagKind.character)
-    for i in range(5):
-        img = _img(f"{i:064d}", [float(i)] * 1152)
-        db.add(img)
-        await db.flush()
-        await _attach(db, img.id, tag.id)
-
-    svc = CentroidService(db)
-    assert await svc.recompute_for_tag(tag.id) is True
-
-    from backend.app.models import TagReferenceEmbedding
-    cen = await db.get(TagReferenceEmbedding, tag.id)
-    assert cen is not None
-    assert cen.reference_count == 5
-    assert abs(np.array(cen.embedding)[0] - 2.0) < 1e-4
-
-
-@pytest.mark.asyncio
-async def test_recompute_skips_ineligible_kind(db):
-    tags = TagService(db)
-    tag = await tags.find_or_create("somearchive", TagKind.archive)
-    for i in range(5):
-        img = _img(f"arch{i:060d}", [1.0] * 1152)
-        db.add(img)
-        await db.flush()
-        await _attach(db, img.id, tag.id)
-    svc = CentroidService(db)
-    assert await svc.recompute_for_tag(tag.id) is False
-
-
-@pytest.mark.asyncio
-async def test_list_drifted_includes_uncomputed(db):
-    tags = TagService(db)
-    tag = await tags.find_or_create("Drifty", TagKind.character)
-    for i in range(5):
-        img = _img(f"d{i:063d}", [0.5] * 1152)
-        db.add(img)
-        await db.flush()
-        await _attach(db, img.id, tag.id)
-    svc = CentroidService(db)
-    drifted = await svc.list_drifted()
-    assert tag.id in drifted
-
-
-@pytest.mark.asyncio
-async def test_find_similar_tags(db):
-    tags = TagService(db)
-    tag = await tags.find_or_create("SimTag", TagKind.character)
-    for i in range(5):
-        img = _img(f"s{i:063d}", [1.0] * 1152)
-        db.add(img)
-        await db.flush()
-        await _attach(db, img.id, tag.id)
-    svc = CentroidService(db)
-    await svc.recompute_for_tag(tag.id)
-
-    query_img = _img("q" * 64, [1.0] * 1152)
-    db.add(query_img)
-    await db.flush()
-    hits = await svc.find_similar_tags(query_img.id, limit=10)
-    assert any(h.tag_id == tag.id for h in hits)
-    sim = next(h.similarity for h in hits if h.tag_id == tag.id)
-    assert sim > 0.99

tests/test_tag_merge.py

@@ -279,34 +279,6 @@ async def test_merge_allowlist_source_only_moves_to_target(db):
     assert rows[0].min_confidence == 0.42
 
 
-@pytest.mark.asyncio
-async def test_merge_deletes_source_embedding(db):
-    from backend.app.models.tag_reference_embedding import (
-        TagReferenceEmbedding,
-    )
-
-    svc = TagService(db)
-    a = await svc.find_or_create("SrcEmb", TagKind.general)
-    b = await svc.find_or_create("TgtEmb", TagKind.general)
-    db.add(
-        TagReferenceEmbedding(
-            tag_id=a.id,
-            embedding=[0.0] * 1152,
-            reference_count=1,
-            model_version="v",
-        )
-    )
-    await db.flush()
-    await svc.merge(a.id, b.id)
-    db.expire_all()  # merge() uses Core DML; drop stale identity-map state
-    remaining = await db.scalar(
-        select(func.count())
-        .select_from(TagReferenceEmbedding)
-        .where(TagReferenceEmbedding.tag_id == a.id)
-    )
-    assert remaining == 0
-
-
 @pytest.mark.asyncio
 async def test_merge_repoints_existing_aliases(db):
     from backend.app.models.tag_alias import TagAlias