With Bitcoin Core's wallet deleted, LND's PSBT round trip is the only
external-signer path Archipelago has, and D-09's key-origin protection moves
from Core descriptors (of which none remain) to the PSBT itself.
Adds `psbt_key_origin_report(&str) -> Result<PsbtKeyOriginReport>` to
lnd/wallet.rs, reporting `input_count`, `inputs_with_key_origin` and
`all_inputs_have_key_origin`. An input counts as carrying key origin when
either its `bip32_derivation` or `tap_key_origins` map is non-empty. A PSBT
with zero inputs reports false rather than vacuous truth. Parsed with the
already-present `bitcoin` and `base64` crates; no dependency added.
`lnd.create-psbt` gains an additive `key_origin` object on its response and a
`tracing::warn!` with the counts when key origin is missing, because that is
the exact condition under which a hardware signer refuses the PSBT. Computed
best-effort: a decode failure degrades to `null`, never to an error, so a
user's send cannot fail because an inspection helper could not parse
something. `handle_lnd_finalize_psbt` and `handle_lnd_create_raw_tx` (which
deliberately auto-signs with LND's hot keys) are untouched.
Three tests, with fixtures built programmatically from the `bitcoin` crate
rather than pasted as opaque base64: with-derivations, without-derivations,
and malformed-is-an-error-not-a-panic.
KEY-03-SIGNING-POSTURE.md gains an honest per-step coverage map of the
fund -> export -> sign offline -> import -> finalize -> broadcast round trip.
Of six steps, only the new inspection has automated coverage; steps 1, 4, 5
and 6 have none, and there is no air-gap transport (no animated QR, no .psbt
file exchange) — export/import is copy-paste of base64. Untested paths are
named as untested.
Records the verdict that decides whether any of this is an air gap: on a
default node an external signer CANNOT meaningfully sign a PSBT from
`lnd.create-psbt`, because LND holds the keys for every input it selects.
Evidence: the PSBT is funded from LND's own wallet; `ensure_wallet_initialized`
creates a full key-holding wallet via /v1/initwallet; the generated lnd.conf
carries no `remotesigner.*` block; and a search of apps/, scripts/,
core/archipelago/src and image-recipe/ for remotesigner/createwatchonly/
nochainbackend returns zero matches. No fleet node is provisioned watch-only.
What ships is PSBT transport, not air-gapped custody — the gap is
provisioning, not plumbing.
Adds the standing honesty statement in its own subsection: Lightning channel,
revocation and HTLC keys are NOT air-gappable at all. They must sign in real
time to answer counterparty commitments; remote signing relocates them to a
hardened host, it does not cool them.
Also adds a status banner to PSBT-SIGNING-ARCHITECTURE.md recording that its
Phase 1 was superseded by deletion rather than delivered, so §0's "single
highest-value change" and §2.1's invariant now read against a code path that
no longer exists. Banner only; §5.4's honesty table is byte-identical.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
