Stored key is lost on Brave browser when hitting F5

As title says... This is the only browser where I have this problem. I have also tested with Brave Shields off for my page.

The issue is about session-keystore losing stored keys on Brave browser when refreshing with F5. Start by examining the browser storage mechanisms used (likely sessionStorage or IndexedDB) in the source code, particularly around persistence and event handling. Reproduce the bug in Brave to confirm, then check for known Brave-specific storage quirks or F5 event differences. Look at existing tests for storage behavior to understand the expected flow.

索引モデルが issue の本文から書いたものです。