Anchor needs documentation on clearing saves in private rooms

In a private anchor room, we began with a vanilla session and then swapped to a romhack in the same roomid. The romhack synced with the vanilla save despite us both using the romhack, and broke the hack entirely. If there is a smooth method for clearing a roomid's synced save data before swapping games, it should be clearly documented.

The issue names no files or tests; start by locating Anchor's private-room save synchronization and the roomid save-data clearing flow. Verify whether a safe clearing method exists, then document the confirmed steps for clearing synced saves before swapping games and make the procedure easy to follow.

Written by the indexing model from the issue text.