fix: JSON reports emit invalid NaN + O(n) rolling window

src/trainpulse/detectors.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import math
+from collections import deque
 
 from trainpulse._types import Alert, AlertSeverity
 
@@ -12,12 +13,10 @@ class RollingWindow:
 
     def __init__(self, size: int) -> None:
         self._size = max(size, 1)
-        self._values: list[float] = []
+        self._values: deque[float] = deque(maxlen=self._size)
 
     def add(self, value: float) -> None:
         self._values.append(value)
-        if len(self._values) > self._size:
-            self._values.pop(0)
 
     @property
     def values(self) -> list[float]:

src/trainpulse/report.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import json
+import math
 from pathlib import Path
 from typing import Any
 
@@ -24,7 +25,7 @@ def report_to_dict(report: TrainingReport) -> dict[str, Any]:
                 "detector": a.detector,
                 "message": a.message,
                 "metric_name": a.metric_name,
-                "metric_value": a.metric_value,
+                "metric_value": a.metric_value if math.isfinite(a.metric_value) else None,
             }
             for a in report.alerts
         ],