abstracted out bounded cycles

tests/test_build_product_details.py

@@ -30,6 +30,9 @@ def _doc(**overrides) -> dict:
         "endDate": None,
         "priceBeforeDrop": None,
         "eduPrice": None,
+        "pastPrices": [
+            {"price": 80.0, "date": datetime(2026, 7, 26, tzinfo=timezone.utc)}
+        ],
         "available": True,
         "condition": None,
         "appExclusive": None,
@@ -103,3 +106,19 @@ def test_dollar_code_does_not_affect_threshold():
         promoMinSpend=100,
     )
     assert build_product_details(doc, min_percentage=40) is None
+
+
+# ----------------------------------------------------------------- pastPrices
+
+
+def test_past_prices_read_through():
+    """Price history passes through unchanged."""
+
+    history = [
+        {"price": 95.0, "date": datetime(2026, 7, 20, tzinfo=timezone.utc)},
+        {"price": 90.0, "date": datetime(2026, 7, 24, tzinfo=timezone.utc)},
+    ]
+
+    product = build_product_details(_doc(pastPrices=history), min_percentage=0)
+
+    assert product.pricing.past_prices == history