fix: keep the postgres backfill from disabling telemetry or locking the table

src/polygateway/transports/openai_compat.py

@@ -178,10 +178,13 @@ def _coerce_cached_tokens(usage: Any) -> int | None:
 
 
 def _coerce_model_reported(value: Any) -> str | None:
-    """取响应体的 model 字段(issue #3);非 str 或空白串一律 None。"""
+    """取响应体的 model 字段(issue #3);非 str 或空白串一律 None,收口时去空白。
+
+    去空白不是洁癖: 下游拿这个串做实验快照的 key,`" m "` 与 `"m"` 会造成假分叉。
+    """
     if not isinstance(value, str) or not value.strip():
         return None
-    return value
+    return value.strip()
 
 
 def _resolve_stream_usage(sink: dict[str, Any], salvaged: bool) -> tuple[int, int, str]: