feat: 按 Vault 隔离桌面检索投影与任务链接

backend/app/database/db.py

@@ -26,8 +26,28 @@ def _load_extension(conn: sqlite3.Connection) -> None:
 
 def connect() -> sqlite3.Connection:
     settings = get_settings()
-    settings.db_path.parent.mkdir(parents=True, exist_ok=True)
-    conn = sqlite3.connect(settings.db_path)
+    return _connect_path(settings.db_path)
+
+
+def connect_knowledge() -> sqlite3.Connection:
+    """Desktop projections never share note or vector rows between Vaults."""
+    settings = get_settings()
+    if settings.environment != 'desktop':
+        return connect()
+    from app import host_bridge
+    from app.errors import ApiError
+    from uuid import UUID
+    try:
+        vault = str(UUID(host_bridge.vault_id.get() or ''))
+    except ValueError:
+        raise ApiError(409, 'WORKSPACE_NOT_OPEN', '请先打开授权工作区。') from None
+    # This database also holds durable logical records (tasks); never delete it as a cache.
+    return _connect_path(settings.data_dir / 'vault-state' / vault / 'core.sqlite3')
+
+
+def _connect_path(path) -> sqlite3.Connection:
+    path.parent.mkdir(parents=True, exist_ok=True)
+    conn = sqlite3.connect(path)
     conn.row_factory = sqlite3.Row
     # 关闭 Python sqlite3 的隐式事务，提交时机由 transaction() 或显式 commit 控制。
     conn.isolation_level = None