Conclusion

Harry crouched by the base of the wall and wedged the edge of the narrow-bladed shovel into the door seam.

He adjusted the angle until the tip ran parallel to the seam, braced the handle with the heel of his palm, and slowly increased the pressure.

The filler broke with a duller sound than he had expected, as though some exceptionally dense material were slowly crumbling under sustained pressure.

Fine grains spilled from the edge of the seam onto the stone floor with a faint rustle.

He pulled the shovel out, shifted to another spot, and pushed it in again.

Ron crouched beside him, set the small vibration head against the edge of the seam, and switched it on.

Its frequency was low but steady. A deep hum formed in the seam, passed through the filler, and traveled along the edge of the door.

Under the sustained low-frequency vibration, the filler began to break apart faster. Cracks spread along the surface where it met the door, forming a dense web of fractures.

Hermione stood behind them, the lighting orb casting a soft halo around her. Her gaze fell on the debris scattered across the floor. "The filler is breaking evenly, not cracking at random. It's coming apart along specific structural lines. When this door was sealed, they may have left an extremely thin separating layer between the filler and the door to keep them from bonding completely."

She crouched too, picked up a small fragment, and turned it over. "This side is lighter than the other. It might be residue from that separating layer."

"Then whoever designed this expected someone to open the door someday, even when they sealed it."

Harry changed the angle of the narrow-bladed shovel and wedged it into the middle of the seam. The filler broke