fix(m3): uuid secure-context fallback + middle-tier SKU business rules

- frontend: uuid() helper (crypto.randomUUID -> getRandomValues) for plain-HTTP LAN UAT
- slabs.py: empty SKU at create -> NULL (no-SKU-yet is transient, filled in Review)
- review.py: ready-gate enforces REVIEW-45 (SKU 3-24 alnum+hyphen) in the middle tier
- DB CHECK stays as backstop only (referential/structural), per layering principle

backend/review.py

@@ -114,8 +114,20 @@ def missing_required(slab: dict) -> list[str]:
     return [f for f in _REQUIRED if slab.get(f) in (None, "", [])]
 
 
+# REVIEW-45: SKU is 3 to 24 chars, alphanumeric and hyphen only. The middle tier
+# (not the DB CHECK) is the business-logic arbiter here; the DB constraint is a backstop.
+_SKU_RE = re.compile(r"^[A-Za-z0-9-]{3,24}$")
+
+
+def sku_valid(sku: Any) -> bool:
+    return isinstance(sku, str) and bool(_SKU_RE.match(sku))
+
+
 def compute_ready(slab: dict) -> tuple[bool, list[str]]:
     missing = missing_required(slab)
+    # A present-but-malformed SKU is not ready (business rule, enforced in the middle tier).
+    if "sku" not in missing and not sku_valid(slab.get("sku")):
+        missing.append("sku")
     return (len(missing) == 0), missing
 
 

backend/slabs.py

@@ -110,8 +110,14 @@ async def create_slab(payload: Dict[str, Any]) -> Dict[str, Any]:
     missing = [f for f in REQUIRED_CREATE_FIELDS if f not in payload]
     if missing:
         return _err("validation", "missing fields", {"fields": missing}, status=400)
+    # Business rule (middle tier, not the DB): an empty/blank SKU at create means
+    # "not set yet" (the owner fills it in Review). Store NULL — the DB CHECK only
+    # governs present SKUs, and NULL is the honest "absent" representation.
+    sku = payload["sku"]
+    if isinstance(sku, str) and sku.strip() == "":
+        payload = {**payload, "sku": None}
     conn = get_connection()
-    if _sku_taken(conn, payload["sku"]):
+    if payload["sku"] is not None and _sku_taken(conn, payload["sku"]):
         return _err("duplicate_sku", "SKU already exists", {"sku": payload["sku"]}, status=409)
     now = _now_iso()
     data = _encode(payload)

backend/tests/test_slabs_api.py

@@ -180,6 +180,50 @@ def test_soft_delete(client, db):
     assert resp_get.status_code == 404
 
 
+def test_create_empty_sku_stored_as_null(client, db):
+    # Business rule (middle tier): empty SKU at create = "not set yet" -> stored as NULL,
+    # not rejected by the DB CHECK. This is the UAT "Continue to Review" path.
+    slab_id = str(uuid.uuid4())
+    payload = {"id": slab_id, "sku": "", "length_in":10,"thickness_in":2,"sqft":20,"bdft":5,"width_min_in":1,"width_max_in":2,"width_avg_in":1.5,"species_id":1,"wood_category_ids":json.dumps([2]),"edge_type_term_id":1,"figure_term_ids":json.dumps([1]),"grade_term_id":1,"thickness_term_id":1,"moisture_term_id":1,"fig_tag_ids":json.dumps([1]),"feat_tag_ids":json.dumps([2]),"price":100,"price_source":"recommendation","title":"Test","short_description":"short","description":"desc","content_source":"manual","species_confidence":0.9,"figure_confidence":0.8,"grade_confidence":0.7,"inference_status":"inferring","calibration_photo_id":None}
+    resp = client.post("/api/v1/slabs", json=payload)
+    assert resp.status_code == 201
+    assert resp.json()["sku"] is None
+    # A second empty-SKU slab is allowed (NULLs are not unique-conflicts).
+    resp2 = client.post("/api/v1/slabs", json={**payload, "id": str(uuid.uuid4())})
+    assert resp2.status_code == 201
+
+
+def test_create_null_sku_allowed(client, db):
+    slab_id = str(uuid.uuid4())
+    payload = {"id": slab_id, "sku": None, "length_in":10,"thickness_in":2,"sqft":20,"bdft":5,"width_min_in":1,"width_max_in":2,"width_avg_in":1.5,"species_id":1,"wood_category_ids":json.dumps([2]),"edge_type_term_id":1,"figure_term_ids":json.dumps([1]),"grade_term_id":1,"thickness_term_id":1,"moisture_term_id":1,"fig_tag_ids":json.dumps([1]),"feat_tag_ids":json.dumps([2]),"price":100,"price_source":"recommendation","title":"Test","short_description":"short","description":"desc","content_source":"manual","species_confidence":0.9,"figure_confidence":0.8,"grade_confidence":0.7,"inference_status":"inferring","calibration_photo_id":None}
+    resp = client.post("/api/v1/slabs", json=payload)
+    assert resp.status_code == 201
+    assert resp.json()["sku"] is None
+
+
+def test_ready_gate_rejects_malformed_sku(client, db):
+    # REVIEW-45 enforced in the middle tier: a present-but-out-of-range/char-set SKU is not ready.
+    from backend.review import compute_ready, sku_valid
+    base = {"length_in":10,"thickness_in":2,"sqft":20,"bdft":5,"width_min_in":1,"width_max_in":2,"width_avg_in":1.5,"species_id":1,"wood_category_ids":json.dumps([2]),"edge_type_term_id":1,"figure_term_ids":json.dumps([1]),"grade_term_id":1,"thickness_term_id":1,"moisture_term_id":1,"price":100,"price_source":"recommendation","title":"Test","short_description":"short","description":"desc","content_source":"manual"}
+    # valid
+    assert sku_valid("AB-1") is True
+    ready, missing = compute_ready({**base, "sku": "AB-1"})
+    assert ready is True and "sku" not in missing
+    # too short
+    assert sku_valid("AB") is False
+    ready, missing = compute_ready({**base, "sku": "AB"})
+    assert ready is False and "sku" in missing
+    # bad char
+    ready, missing = compute_ready({**base, "sku": "AB!"})
+    assert ready is False and "sku" in missing
+    # too long
+    ready, missing = compute_ready({**base, "sku": "A" * 25})
+    assert ready is False and "sku" in missing
+    # missing (None)
+    ready, missing = compute_ready({**base, "sku": None})
+    assert ready is False and "sku" in missing
+
+
 def test_delete_published_conflict(client, db):
     slab_id = str(uuid.uuid4())
     payload = {"id": slab_id, "sku": "SKU001", "length_in":10,"thickness_in":2,"sqft":20,"bdft":5,"width_min_in":1,"width_max_in":2,"width_avg_in":1.5,"species_id":1,"wood_category_ids":json.dumps([2]),"edge_type_term_id":1,"figure_term_ids":json.dumps([1]),"grade_term_id":1,"thickness_term_id":1,"moisture_term_id":1,"fig_tag_ids":json.dumps([1]),"feat_tag_ids":json.dumps([2]),"price":100,"price_source":"recommendation","title":"Test","short_description":"short","description":"desc","content_source":"manual","species_confidence":0.9,"figure_confidence":0.8,"grade_confidence":0.7,"inference_status":"inferring","calibration_photo_id":None}