One-time secret
Paste a password or key and get back a link that works exactly once. Opening it destroys the contents — not a flag saying it was read, the encrypted blob itself. Everything is encrypted in this browser tab, so the link alone is useless without the passphrase, and we could not read your secret if we wanted to.
Passwords sent over chat or email stay there. They sit in a searchable archive on at least two machines, get quoted into replies, and outlive the reason they were sent. A one-time link is the opposite: it exists to stop existing.
Send the link and the passphrase separately. That is the whole security model. Someone who intercepts one channel has nothing. Put the link in email and read the passphrase aloud, or send it by text.
Need a secret that lasts — one your coding agent can use again tomorrow without you pasting it every time? That is what the vault is for.