A signed checkpoint inside the same database is still only as strong as that
file. Store(..., anchor_path=) / SIGIL_ANCHOR now writes the signed tip to a
filesystem path outside the DB (atomic tip file + append-only .log).
verify_external_anchors catches a rewrite even after in-DB checkpoints are
deleted. 8 new tests in test_anchor.py; suite 119 green.
Part of Quarry 18a5d762 (Sigil prod build). Do not merge to main yet:
sealed store and independent crypto review still open.
Replace passcode identity with Ed25519 challenge-response.
- Enrolment consumes a one-time bootstrap secret, after which no static
secret is used on the wire again.
- Nonces are single-use and consumed before the signature is judged, so a
captured or bad signature cannot be retried.
- Sessions are short-lived, scoped, and typed agent vs human_via_agent.
- Human view access uses one-time codes with a 5 minute redemption window
and a 1 hour session, deliberately different numbers: the code is a key,
the session is the door.
- Invariant: only an agent signature may act as an agent. Enforced and tested.
- Append-only audit trail.
54 tests, covering refusals rather than only the happy path.
Reference implementation, not reviewed or hardened. See README Status.
