fix(mcp): guard tool_status/list_wings/list_rooms/get_taxonomy against None metadata

Four more MCP handlers iterate a metadata list and call m.get(...)
unconditionally. When the cache contains a None entry (drawers with no
metadata, common on older mining paths), the try block catches the
AttributeError and marks the response "partial: true" with an
error message — visible as {"error": "'NoneType' object has no
attribute 'get'", "partial": true} returned from mempalace_status even
though the palace data is otherwise fetchable.

Same m = m or {} guard we applied to searcher.py (d3a2d22, a51c3c2)
and miner.status() (66f08a1). None-metadata drawers now roll up under
the existing "unknown" fallback bucket instead of poisoning the
response with a misleading partial flag.

Regression test: mock the metadata cache with a None in the middle,
assert tool_status returns clean counts and no error/partial fields.
Verified the test fails without the guard.

998 tests pass.

tests/test_mcp_server.py

@@ -250,6 +250,38 @@ class TestReadTools:
         assert "project" in result["wings"]
         assert "notes" in result["wings"]
 
+    def test_status_handles_none_metadata_without_partial(
+        self, monkeypatch, config, palace_path, kg
+    ):
+        """tool_status must not crash or go partial when the metadata cache
+        returns a ``None`` entry — palaces can contain drawers with no
+        metadata (older mining paths, third-party writes). Before the guard,
+        ``m.get("wing")`` raised AttributeError mid-tally and the result
+        carried ``"error"`` + ``"partial": True`` even though the data was
+        perfectly fetchable."""
+        from unittest.mock import patch as _patch
+
+        _patch_mcp_server(monkeypatch, config, kg)
+        from mempalace.mcp_server import tool_status
+
+        # Inject a metadata cache where one entry is None
+        with _patch("mempalace.mcp_server._get_collection") as mock_get_col:
+            fake_col = type("C", (), {"count": lambda self: 2})()
+            mock_get_col.return_value = fake_col
+            with _patch(
+                "mempalace.mcp_server._get_cached_metadata",
+                return_value=[{"wing": "proj", "room": "r"}, None],
+            ):
+                result = tool_status()
+
+        # The None-metadata drawer falls under 'unknown/unknown' — no crash,
+        # no partial flag.
+        assert "error" not in result
+        assert result.get("partial") is not True
+        assert result["total_drawers"] == 2
+        assert result["wings"].get("proj") == 1
+        assert result["wings"].get("unknown") == 1
+
     def test_list_wings(self, monkeypatch, config, palace_path, seeded_collection, kg):
         _patch_mcp_server(monkeypatch, config, kg)
         from mempalace.mcp_server import tool_list_wings