Just so we're on the same page: if both parties are offline the ecash can be double-spent. CashuMe allows the sender to delete the token upon sending so that the receiver can have more confidence that it won't be double-spent while they're offline. More:

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Cashu.me 0.1 – Release notes

Cashu.me 0.1 – Release notes. GitHub Gist: instantly share code, notes, and snippets.