This game really reminded me of the Thief series, which I love for the atmosphere even more than the actual gameplay. The sigil mechanic is great and could easily form the basis for various puzzles in an extended version.
Last but not least, your method of guiding the player to keep the cursor aligned is ingenious. This is a frustrating problem I face with every single Godot game exported to HTML5 (including my own, Gridscryer), where no standard mouse-capture mode seems to provide a proper solution.
Great game!