TBH, the best pattern I've seen is just nuking the secrets at the input level. Run a local regex watcher in-memory that flags anything looking like a PK or seed phrase before it even hits the agent's context window. Keeps it off the network stack entirely
Any prompt injection attack could by pass this by simply do a base64 or any encoding, I guess?
You ar absolutely right. Obfuscation like Base64 or rot13 will always beat static Regex. I was thinking more in terms of a seatbelt for accidental leaks user error rather than a defense against adversarial prompt injection. It's about reducing the blast radius of clumsy mistakes, not stopping a determined attacker.