Packet authorship: sign and verify senders without hosted identity #12

Goal

Prove who authored a packet or delivery, not only that bytes are unchanged (SHA-256) or that a local: label was written.

Problem

Today:

• SHA-256 detects tampering in transit, not authorship.
• Durable inbox local:name is a routing label, not authenticated identity.
• Anyone who can write the mailbox can forge a delivery that looks structurally valid.

That is honest for a local spool; it is insufficient for multi-user or remote transport.

Scope

• Local keypair (or equivalent) managed by the user/agent environment — no 3Notch account system.
• Sign packed packets / deliveries at send time; verify on pull/import.
• Surface verification status in CLI (packet preview, inbox pull, status) and MCP structured results.
• Document trust model: keys, TOFU vs pinned identities, rotation, what verify-fail does (fail closed by default for remote/sealed paths).

Non-goals

• OAuth, org SSO, or hosted identity provider in core.
• Treating signature as encryption (separate issue).
• Replacing human review of packet content.

Acceptance ideas

• Spec for signature envelope (what is signed, where keys live, algorithm).
• Create/sign and verify paths with unit + e2e coverage.
• Clear errors for missing key, untrusted key, and bad signature.
• Docs: how two agents on different machines exchange/pin public keys.

Related

• Builds on encryption work for key hygiene but can design in parallel.
• Required before remote transport claims "authenticated delivery."
• Does not change the intentional block of private/seed on open shared mailboxes.