feat: restore source parity and harden agent runtime

backend-fastapi/online_dev/report_manager/engine/preview_guard.py

@@ -0,0 +1,43 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+"""预览/导出非功能性护栏（阶段 G）"""
+from __future__ import annotations
+
+from typing import Any, Dict, List
+
+# 与 dataset_bridge.fetch_all max_rows 对齐
+DEFAULT_MAX_DATASET_ROWS = 50000
+WARN_DATASET_ROWS = 10000
+WARN_SNAPSHOT_CELL_COUNT = 200_000
+
+
+def estimate_snapshot_cell_count(snapshot: Dict[str, Any]) -> int:
+    total = 0
+    for sheet in (snapshot.get("sheets") or {}).values():
+        if not isinstance(sheet, dict):
+            continue
+        for row in (sheet.get("cellData") or {}).values():
+            if isinstance(row, dict):
+                total += len(row)
+    return total
+
+
+def collect_preview_warnings(
+    *,
+    datasets: Dict[str, List[Any]],
+    snapshot: Dict[str, Any],
+    max_rows: int = DEFAULT_MAX_DATASET_ROWS,
+    warn_rows: int = WARN_DATASET_ROWS,
+) -> List[str]:
+    """返回 warning 码列表，供前端 i18n 映射。"""
+    warnings: List[str] = []
+    for alias, rows in (datasets or {}).items():
+        count = len(rows) if isinstance(rows, list) else 0
+        if count >= max_rows:
+            warnings.append(f"dataset_row_limit:{alias}")
+        elif count >= warn_rows:
+            warnings.append(f"dataset_row_warn:{alias}")
+    cell_count = estimate_snapshot_cell_count(snapshot or {})
+    if cell_count >= WARN_SNAPSHOT_CELL_COUNT:
+        warnings.append("snapshot_large")
+    return warnings