fix high priority issues

bincio/extract/writer.py

@@ -83,6 +83,13 @@ def write_activity(
     }
 
     json_path = acts_dir / f"{activity_id}.json"
+    # Collision guard: if a *different* activity already has this ID, append a
+    # short hash suffix to disambiguate (same hash = idempotent re-extract).
+    if json_path.exists():
+        existing = json.loads(json_path.read_text(encoding="utf-8"))
+        if existing.get("source_hash") != activity.source_hash:
+            activity_id = f"{activity_id}-{activity.source_hash[-6:]}"
+            json_path = acts_dir / f"{activity_id}.json"
     json_path.write_text(json.dumps(detail, indent=2, ensure_ascii=False))
 
     # ── GeoJSON track ────────────────────────────────────────────────────────