docs: Clarify offline recovery preparation

Require the signer to have the chain history needed for a rescan before it is air-gapped, and avoid a redundant standalone card check before ms32 wallet performs recovery validation.

Refs #93.

Author: BenWestgate

docs/user/guide.md

@@ -200,9 +200,10 @@ worth the extra steps.
 ## More protection: watch-only wallet and offline signer
 
 On the offline signer, create an empty encrypted descriptor wallet with private
-keys enabled and run `ms32 wallet`. Keep that computer permanently disconnected
-from every network as soon as Bitcoin Core and codex32 are installed and
-disconnect before recovery text or signing keys are present.
+keys enabled and run `ms32 wallet`. If this signer may need to rescan an
+existing wallet, synchronize Bitcoin Core or copy in the required chain history
+before making the signer permanently offline. Then disconnect every network
+path before entering recovery text or exposing signing keys.
 
 After the signer is restored, follow Bitcoin Core's maintained
 [offline-signing tutorial](https://github.com/bitcoin/bitcoin/blob/master/doc/offline-signing-tutorial.md).
@@ -224,12 +225,11 @@ its public wallet data with the separate wallet record.
 1. Collect the required cards with matching identifiers and text lengths.
 2. Find the separately stored wallet record and the original wallet
    instructions.
-3. On Tails or another reviewed offline computer, check each card with
-   `ms32 check`. If validation fails, recheck what you typed before assuming
-   the paper is wrong.
-4. Disable Ethernet, internet, Tor, Wi-Fi, Bluetooth, cellular, and every other
-   network path. Load a blank encrypted descriptor wallet with private keys
-   enabled in Bitcoin Core, and run:
+3. Before entering recovery text, ensure the offline signer already has the
+   Bitcoin Core chain history needed for the requested rescan. Then disable
+   Ethernet, internet, Tor, Wi-Fi, Bluetooth, cellular, and every other network
+   path. Load a blank encrypted descriptor wallet with private keys enabled in
+   Bitcoin Core, and run:
 
    ```bash
    ms32 wallet --timestamp 0
@@ -238,11 +238,11 @@ its public wallet data with the separate wallet record.
    If you know when the wallet was first used, an earlier Unix timestamp can
    shorten the rescan; `0` remains the safest choice when unsure.
 
-5. Select and confirm that wallet. If it is locked, follow the displayed
+4. Select and confirm that wallet. If it is locked, follow the displayed
    Bitcoin-Qt Console instructions; codex32 waits and continues automatically.
    It gives Core the master private key, asks Core to create the standard
    account-0 descriptors, scans history, and relocks an encrypted wallet.
-6. If you need an online watch-only counterpart, keep the restored signer
+5. If you need an online watch-only counterpart, keep the restored signer
    offline and follow Bitcoin Core's
    [offline-signing tutorial](https://github.com/bitcoin/bitcoin/blob/master/doc/offline-signing-tutorial.md)
    to export and restore the watch-only wallet. Let the online node synchronize,