parallelizing extraction, fix tcx files

bincio/extract/writer.py

@@ -12,11 +12,13 @@ from bincio.extract.timeseries import build_timeseries
 
 
 def make_activity_id(activity: ParsedActivity) -> str:
-    """Generate a BAS activity ID from started_at + optional title slug."""
-    ts = activity.started_at
-    # Compact ISO format: 2024-06-01T073012+0200
-    tz_str = ts.strftime("%z")  # e.g. "+0200" or ""
-    ts_part = ts.strftime("%Y-%m-%dT%H%M%S") + (tz_str or "Z")
+    """Generate a BAS activity ID from started_at + optional title slug.
+
+    Always uses UTC with Z suffix so IDs are URL-safe (no + chars).
+    """
+    from datetime import timezone
+    ts = activity.started_at.astimezone(timezone.utc)
+    ts_part = ts.strftime("%Y-%m-%dT%H%M%SZ")
 
     if activity.title:
         slug = _slugify(activity.title)