docs: default visible columns contract (v1.0.79)

沉淀 _jiangchang_tables.default_visible_columns_json：技能声明默认展示列；未配置全显；用户改「列」后本机覆盖；与 visible=0 硬隐藏区分。

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_display_metadata.py

@@ -507,6 +507,54 @@ metadata:
         self.assertIn("seed_column_metadata_batch", text)
         self.assertIn("valid_column_names", text)
 
+    def test_default_visible_columns_json_upsert_and_migrate(self) -> None:
+        conn = sqlite3.connect(":memory:")
+        try:
+            from db.display_metadata import (
+                init_display_metadata_tables,
+                upsert_table_metadata,
+            )
+
+            cur = conn.cursor()
+            # Simulate pre-1.0.79 table without the new column.
+            cur.execute(
+                """
+                CREATE TABLE _jiangchang_tables (
+                    table_name TEXT PRIMARY KEY,
+                    display_name TEXT NOT NULL,
+                    description TEXT,
+                    sort_order INTEGER,
+                    visible INTEGER NOT NULL DEFAULT 1,
+                    readonly INTEGER NOT NULL DEFAULT 0,
+                    default_sort_json TEXT
+                )
+                """
+            )
+            init_display_metadata_tables(cur)
+            cur.execute("PRAGMA table_info('_jiangchang_tables')")
+            cols = {str(row[1]) for row in cur.fetchall()}
+            self.assertIn("default_visible_columns_json", cols)
+
+            payload = '["stat_type","period","stage"]'
+            upsert_table_metadata(
+                cur,
+                table_name="timeliness_stats",
+                display_name="时效统计",
+                readonly=1,
+                default_visible_columns_json=payload,
+            )
+            conn.commit()
+            cur.execute(
+                """
+                SELECT default_visible_columns_json
+                FROM _jiangchang_tables
+                WHERE table_name = 'timeliness_stats'
+                """
+            )
+            self.assertEqual(cur.fetchone()[0], payload)
+        finally:
+            conn.close()
+
 
 if __name__ == "__main__":
     unittest.main()