fix: guard parse_token_int against IEEE 754 special floats (#875)

src/copilot_usage/models.py

@@ -6,6 +6,7 @@
 """
 
 import builtins
+import math
 from datetime import UTC, datetime
 from enum import StrEnum
 from pathlib import Path
@@ -220,6 +221,7 @@ def parse_token_int(raw: object) -> int | None:
     Rules:
 
     - ``bool`` / ``str`` → ``None`` (invalid, not coerced)
+    - IEEE 754 special ``float`` (``inf``, ``-inf``, ``nan``) → ``None``
     - non-whole ``float`` → ``None``
     - zero or negative ``int`` / ``float`` → ``None``
     - positive whole-number ``float`` → coerced to ``int``
@@ -229,6 +231,8 @@ def parse_token_int(raw: object) -> int | None:
     if isinstance(raw, (bool, str)):
         return None
     if isinstance(raw, float):
+        if not math.isfinite(raw):
+            return None
         if not raw.is_integer():
             return None
         tokens = int(raw)

tests/copilot_usage/test_parser.py

@@ -4948,6 +4948,11 @@ def test_returns_none_for_missing_key(self) -> None:
         )
         assert _extract_output_tokens(ev) is None
 
+    @pytest.mark.parametrize("special", [float("inf"), float("nan"), float("-inf")])
+    def test_returns_none_for_ieee_special_floats(self, special: float) -> None:
+        """IEEE 754 special floats (inf, nan, -inf) are not valid token counts."""
+        assert _extract_output_tokens(_make_assistant_event(special)) is None
+
 
 _EXTRACT_TOKENS_CASES: list[tuple[str, object, int | None]] = [
     ("valid_int", 42, 42),
@@ -5021,6 +5026,9 @@ def test_missing_key_no_pydantic(self) -> None:
     ("large_positive_int", 1234),
     ("whole_float", 1234.0),
     ("fractional_float", 3.14),
+    ("float_inf", float("inf")),
+    ("float_neg_inf", float("-inf")),
+    ("float_nan", float("nan")),
 ]