fix(mcp): handle string chartId in layout and non-dict position_json

- _find_chart_keys now matches chartId as both int and str to handle
  imported/hand-edited layouts where chartId may be stored as a string
- validate position_json parses to a dict before passing to layout helpers,
  preventing AttributeError on malformed-but-valid JSON (e.g. "[]")
- test: add return type annotation to mock_auth fixture; add docstrings
  to _chart_node and _call_remove test helpers

Addresses CodeAnt AI review findings on #40958.

Author: aminghadersohi

superset/mcp_service/dashboard/tool/remove_chart_from_dashboard.py

@@ -59,12 +59,14 @@ def _find_chart_keys(layout: Dict[str, Any], chart_id: int) -> list[str]:
     A chart can legitimately appear more than once in a layout (e.g. under
     multiple tabs), so all occurrences are returned.
     """
+    # Accept both int and string chartId — position_json is user/frontend-authored
+    # and imported or hand-edited layouts may store chartId as a string.
     return [
         key
         for key, node in layout.items()
         if isinstance(node, dict)
         and node.get("type") == "CHART"
-        and (node.get("meta") or {}).get("chartId") == chart_id
+        and (node.get("meta") or {}).get("chartId") in (chart_id, str(chart_id))
     ]
 
 
@@ -270,6 +272,8 @@ def remove_chart_from_dashboard(  # noqa: C901 — complexity is structural (lay
                 current_layout = json.loads(dashboard.position_json or "{}")
             except (json.JSONDecodeError, TypeError):
                 current_layout = {}
+            if not isinstance(current_layout, dict):
+                current_layout = {}
 
             remaining_slices = [
                 slc for slc in dashboard.slices if slc.id != request.chart_id

tests/unit_tests/mcp_service/dashboard/tool/test_remove_chart_from_dashboard.py

@@ -35,6 +35,7 @@
 """
 
 import logging
+from collections.abc import Generator
 from typing import Any
 from unittest.mock import Mock, patch
 
@@ -64,7 +65,7 @@ def mcp_server() -> object:
 
 
 @pytest.fixture(autouse=True)
-def mock_auth():
+def mock_auth() -> Generator[Mock, None, None]:
     """Mock authentication for all tests."""
     with patch("superset.mcp_service.auth.get_user_from_request") as mock_get_user:
         mock_user = Mock()
@@ -127,6 +128,7 @@ def _mock_dashboard(
 
 
 def _chart_node(key: str, chart_id: int, parents: list[str]) -> dict[str, Any]:
+    """Build a minimal CHART layout node dict for use in test layouts."""
     return {
         "children": [],
         "id": key,
@@ -254,6 +256,7 @@ def _tabbed_layout() -> dict[str, Any]:
 async def _call_remove(
     mcp_server: object, dashboard_id: int = 1, chart_id: int = 10
 ) -> dict[str, Any]:
+    """Call remove_chart_from_dashboard via the MCP client and return structured content."""
     async with Client(mcp_server) as client:
         result = await client.call_tool(
             "remove_chart_from_dashboard",