--key PATH to check against a key you obtained another way. That is the difference between “this file is internally consistent” and “this was signed by the key I expected”; without --key the verifier trusts the key inside the artifact, which is exactly what someone who does not trust you should not do.
A receipt is about 1.5 KB at ten thousand entries: the entry, its Merkle path, and the signed head that anchors it. A packet adds a title, a digest and a summary of the task, and is the artifact to hand to another person.
Pins
A receipt proves one entry sits in the tree whose head this key signed. A pin proves the log was not rewritten below a head you kept elsewhere.verify --pin recomputes the prefix root and refuses a log that was rewritten below the pin. The check is against the local log; comparing two heads alone, offline, waits for a consistency proof this release does not ship. Store head.json on another device, or in a repository the agent cannot write. A pin beside the ledger is not independent.
What each artifact proves
Signing methods
A record names which signer it carries, and the verifier refuses a combination it does not recognise.
A record that claims human authority must carry a WebAuthn assertion. A local or CI key is not interchangeable with one, even when both verify.
The limit, stated plainly
The signing key lives in.attesso/key.json, in the same directory as the log. Anything that can write the log can write a new one and sign it. A receipt proves the entry is in the log whose head this key signed; it does not prove a human approved it.
It cannot see absence either: a process that deletes the whole directory leaves nothing to verify. If that matters for the decision in front of you, the record has to live where you do not control it.
Hosted Attesso is where authority lives: a passkey approval binds a named human to exact terms, the decision and the refusal are recorded server-side, and the result is evidence a third party verifies offline against a published key. The local ledger uses the same event and code vocabulary, so it can be submitted there later. That chain is described under verify evidence and core model.