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>

src/monitor_utils/runner.py

@@ -1,5 +1,6 @@
 import asyncio
 import logging
+import math
 from collections.abc import Awaitable, Callable, Iterable
 from contextlib import asynccontextmanager, nullcontext
 
@@ -160,7 +161,10 @@ def build_product_details(
 ) -> Product | None:
     """Build a Product from a Mongo document if it passes discount thresholds.
 
-    Skips documents with a missing or zero original price. Passing requires
+    Skips documents with a missing or zero original price, a non-finite
+    price, or a discount too large to represent: a retailer field like
+    "Infinity" survives float(), and the percentage math used to raise
+    OverflowError out of every caller. Passing requires
     meeting min_percentage, or min_price_drop when provided. The caller may
     bypass both thresholds (new listings send at any discount for monitors
     that opt in); which alerts qualify is the caller's decision, not read
@@ -173,7 +177,7 @@ def build_product_details(
         min_percentage: Minimum discount percentage to pass.
         min_price_drop: Optional minimum absolute price drop to pass.
         bypass_thresholds: Build the product even when it fails both
-            thresholds. The missing-price skip still applies.
+            thresholds. The missing- and non-finite-price skips still apply.
 
     Returns:
         The built Product, or None when skipped or below thresholds.
@@ -191,6 +195,19 @@ def build_product_details(
         )
         return
 
+    # Skipped on BOTH paths, not just the percentage one: an MSRP-less product
+    # would otherwise carry the infinite price into its payload. Only floats can
+    # be non-finite, so ints and other types keep their existing behaviour.
+    if any(
+        isinstance(price, float) and not math.isfinite(price)
+        for price in (current_price, original_price)
+    ):
+        LOGGER.warning(
+            "non-finite price, skipping",
+            extra={"product_id": product_id},
+        )
+        return
+
     percentage = 0
     # Defaulted, not indexed: documents written before the field existed have no
     # hasMsrp at all, and stale ones that drop out of a monitor's feed are never
@@ -198,7 +215,15 @@ def build_product_details(
     # pre-existing threshold path rather than silently routing them as MSRP-less.
     has_msrp = product.get("hasMsrp", True)
     if has_msrp:
-        percentage = int(((original_price - current_price) / original_price) * 100)
+        discount = ((original_price - current_price) / original_price) * 100
+        if not math.isfinite(discount):
+            LOGGER.warning(
+                "discount not representable, skipping",
+                extra={"product_id": product_id},
+            )
+            return
+
+        percentage = int(discount)
         price_drop = original_price - current_price
         # A percentage code compounds onto the sale price, so an item can clear the
         # threshold on the combined discount even when the base discount would not.

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