build_product_details: skip non-finite prices instead of raising OverflowError

PR #25 guarded calculate_priority but missed the same calculation here.
On 2026-10-09 06:25:50Z the consumer hit a product with an infinite price;
runner.py:201

    percentage = int(((original_price - current_price) / original_price) * 100)

raised `OverflowError: cannot convert float infinity to integer`. The
Discord leg dropped that one alert, but the API leg's caller does not
catch OverflowError, so the exception escaped and the consumer logged
CRITICAL "api deal loop stopped" -- no deals reached the API from then on
(nothing sent at all after 22:00Z), while the bot itself stayed "alive".

build_product_details now returns None (with a warning, like the
existing missing-price skip) when either price is a non-finite float, on
BOTH paths: the MSRP-less path never computes a percentage and would
otherwise carry inf into the Product and the API payload. A finite pair
whose ratio still overflows (a subnormal original price) is skipped too.
Ints and other types keep their existing behaviour.

Tests (tests/test_build_product_details.py): five new cases fail on the
old code -- OverflowError, ValueError for nan, and the MSRP-less case
building a Product with inf -- and all 25 pass now. Ruff findings on the
two files are unchanged from main (5, all pre-existing).

Rebuild every service that installs monitor-utils with --no-cache to pick
this up (it is pulled unpinned from main).

Co-Authored-By: Claude Code Opus 5.5 (ansible-ops, auto-repair) <noreply@anthropic.com>
Signed-off-by: disqualifier <dev@disqualifier.me>

tests/test_build_product_details.py

@@ -203,3 +203,41 @@ def test_msrpless_doc_with_prices_builds_unthresholded():
     product = build_product_details(doc, min_percentage=40)
     assert product is not None
     assert product.pricing.has_msrp is False
+
+
+# ------------------------------------------------------------ non-finite prices
+
+
+def test_infinite_price_skips_instead_of_raising():
+    """Regression (2026-10-09 06:25Z): float("Infinity") from a retailer field
+    raised OverflowError here and stopped the consumer's API deal loop."""
+
+    inf = float("inf")
+    assert build_product_details(_doc(originalPrice=inf), min_percentage=40) is None
+    assert build_product_details(_doc(currentPrice=inf), min_percentage=40) is None
+    assert build_product_details(_doc(currentPrice=-inf), min_percentage=40) is None
+
+
+def test_nan_price_skips_instead_of_raising():
+    nan = float("nan")
+    assert build_product_details(_doc(currentPrice=nan), min_percentage=40) is None
+    assert build_product_details(_doc(originalPrice=nan), min_percentage=40) is None
+
+
+def test_msrpless_infinite_price_skips_rather_than_reaching_the_payload():
+    """Without the skip the MSRP-less path would carry inf into the Product."""
+
+    doc = _doc(hasMsrp=False, currentPrice=float("inf"))
+    assert build_product_details(doc, min_percentage=40) is None
+
+
+def test_bypass_does_not_rescue_a_non_finite_price():
+    doc = _doc(originalPrice=float("inf"))
+    assert build_product_details(doc, min_percentage=40, bypass_thresholds=True) is None
+
+
+def test_unrepresentable_discount_skips_instead_of_raising():
+    """Finite prices can still overflow the ratio (a subnormal original)."""
+
+    doc = _doc(currentPrice=-1e308, originalPrice=5e-324)
+    assert build_product_details(doc, min_percentage=40) is None