calculate_priority: resolve non-finite prices to 0 instead of crashing the monitor

tpv-academysports died on 2026-10-08 06:27 UTC and stayed down: six
identical crashes in 8 minutes (each ~2 min after start), then docker's
on-failure:5 gave up. Every one was

    database.py, in calculate_priority
        percentage = int(((original_price - current_price) / original_price) * 100)
    OverflowError: cannot convert float infinity to integer

A monitor builds prices with float() on the retailer's raw field, and
float() accepts "Infinity" / "1e999", so a non-finite price reaches here.
The `not original_price` guard catches None and 0, not inf or nan, and the
exception escapes add_products_to_database -> run_monitor_cycle and kills
the whole process -- one bad product takes the monitor down, and it
crashes again on every restart while that product is listed. Every
monitor that uses this lib has the same exposure.

calculate_priority now returns 0 (the existing "broken prices" bucket)
for a non-finite current/original price, and for a finite pair whose
ratio still overflows (a subnormal original price). Tests cover both;
they fail on the old code (OverflowError, plus ValueError for nan) and
pass now (tests/test_alert_priority.py: 10 passed).

Not changed: the monitor-side float() parsing, which could reject these
prices before they are stored -- worth a look by the monitor owners.

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

tests/test_alert_priority.py

@@ -50,6 +50,23 @@ def test_broken_prices_still_outrank_nothing():
     assert calculate_priority(document(None, 100.0, hasMsrp=False)) == 0
 
 
+def test_non_finite_prices_resolve_to_zero_instead_of_raising():
+    """float("Infinity") from a retailer field once crashed the whole monitor."""
+    inf, nan = float("inf"), float("nan")
+    assert calculate_priority(document(50.0, inf)) == 0
+    assert calculate_priority(document(inf, 100.0)) == 0
+    assert calculate_priority(document(-inf, 100.0)) == 0
+    assert calculate_priority(document(nan, 100.0)) == 0
+    assert calculate_priority(document(50.0, nan)) == 0
+    assert calculate_priority(document(50.0, inf, newListing=True)) == 0
+
+
+def test_a_discount_too_large_to_represent_resolves_to_zero():
+    """Finite prices can still overflow the ratio (a subnormal original)."""
+    assert calculate_priority(document(-1e308, 5e-324)) == 0
+    assert calculate_priority(document(1e308, 5e-324)) == 0
+
+
 def test_new_listing_is_floored_not_buried():
     """A low-discount new listing sends regardless, so it must not sort last."""
     assert (