feat(ml): operator model swap — GPU re-embed + embedder as a setting (#1190)

Make the SigLIP embedder an operator choice (drop-in to SigLIP 2:
google/siglip2-so400m-patch16-512 is a verified 1152-d model at 512px → no
schema change, better small-cue fidelity). A swap = set model + re-embed +
retrain, all operator-driven; the GPU agent does the re-embed so it's fast.

- settings: embedder_model_name is now a setting (migration 0065) alongside the
  existing embedder_model_version; both editable + validated (non-empty) in the
  ml admin API. The server embedder loads by HF name (AutoImageProcessor/Model,
  model-agnostic), preferring the pre-downloaded local dir for the default so
  existing deploys don't re-download; rebuilds on a name change.
- agent: new 'embed' job = whole-image SigLIP embedding (mean-pool video frames)
  under the lease-announced model → POST /jobs/submit_embedding writes
  image_record.siglip_embedding + siglip_model_version. The lease now announces
  the model FROM THE SETTING (not a constant).
- re-embed routing: enqueue_gpu_backfill('embed') selects unembedded + stale-
  version images; 'siglip' now re-embeds concept crops whose version != current
  (so a swap re-triggers crops, not just the never-embedded back-catalogue). The
  CPU ml-worker backfill no longer re-embeds on a version mismatch (it can't
  churn the library at 512px) — the GPU agent owns version re-embeds. Daily
  'embed' + 'siglip' beats self-heal.
- scoring: score_image only bags embeddings in the CURRENT model's space (whole-
  image gated by siglip_model_version, concept regions by embedding_version) so a
  mid-swap stale vector isn't scored by new-space heads; legacy NULL = current.
- UI: GpuAgentCard "Embedding model (advanced)" — edit name/version, Save, and
  "Re-embed library (GPU)" (queues embed + siglip); points at SigLIP 2.

Tests: lease announces model + submit_embedding round-trip; enqueue 'embed'
selects stale/unembedded; stale-version excluded from scoring; embedder model
settable + empty rejected; siglip gate updated to current-version concept.

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

tests/test_gpu_jobs.py

@@ -25,13 +25,17 @@ async def test_enqueue_siglip_backfill_gates_on_concept_region(db):
     # 'siglip' backfill enqueues images that lack a concept region (the
     # back-catalogue) and skips ones that already have one — and never double-
     # enqueues an image that already has a pending siglip job.
+    from backend.app.models import MLSettings
     from backend.app.tasks.ml import enqueue_gpu_backfill
 
+    cur = (await db.execute(
+        select(MLSettings.embedder_model_version).where(MLSettings.id == 1)
+    )).scalar_one()
     need = await _img(db, "e1" * 32)          # no concept region → wants one
-    have = await _img(db, "e2" * 32)          # already embedded → skip
+    have = await _img(db, "e2" * 32)          # concept @ current version → skip
     db.add(ImageRegion(
         image_record_id=have.id, kind="concept", rx=0.0, ry=0.0, rw=1.0, rh=1.0,
-        siglip_embedding=[0.0] * 1152, embedding_version="siglip-test",
+        siglip_embedding=[0.0] * 1152, embedding_version=cur,
     ))
     await db.commit()
 
@@ -57,6 +61,36 @@ async def test_enqueue_siglip_backfill_gates_on_concept_region(db):
     assert n_for_need == 1
 
 
+@pytest.mark.asyncio
+async def test_enqueue_embed_backfill_selects_stale_and_unembedded(db):
+    # Whole-image GPU re-embed (#1190): enqueue images with no embedding or one
+    # stamped under a DIFFERENT model version (an operator swap); skip ones
+    # already at the current version.
+    from backend.app.models import MLSettings
+    from backend.app.tasks.ml import enqueue_gpu_backfill
+
+    cur = (await db.execute(
+        select(MLSettings.embedder_model_version).where(MLSettings.id == 1)
+    )).scalar_one()
+    current = await _img(db, "f1" * 32)
+    current.siglip_embedding = [0.0] * 1152
+    current.siglip_model_version = cur                 # up to date → skip
+    stale = await _img(db, "f2" * 32)
+    stale.siglip_embedding = [0.0] * 1152
+    stale.siglip_model_version = "old-embedder-v0"      # wrong space → re-embed
+    unembedded = await _img(db, "f3" * 32)             # never embedded → embed
+    await db.commit()
+
+    assert enqueue_gpu_backfill("embed") >= 2
+    queued = {
+        j.image_record_id for j in (
+            await db.execute(select(GpuJob).where(GpuJob.task == "embed"))
+        ).scalars()
+    }
+    assert stale.id in queued and unembedded.id in queued
+    assert current.id not in queued
+
+
 @pytest.mark.asyncio
 async def test_enqueue_dedupes_same_pair(db):
     img = await _img(db, "a" * 64)