feat(app): the recovery phrase's words typed back are suggested from BIP-39's list (ADR 0017)

Each of the three fields suggests the words of BIP-39's whole English
list beginning with what is typed, never the phrase's own, and refuses a
word not on it as its field is left, so that a typo is caught before the
words are compared.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

docs/adr/0017-password-totp-and-keys.md

@@ -712,6 +712,21 @@ screenshots, but not out of ScreenCaptureKit's captures on macOS 15 and later; o
 covered in the app switcher's picture, screenshots and recordings not held back; on
 Linux not at all.
 
+
+## The words typed back, suggested from the list (29 Oct 2026, the developer's)
+
+Each of the three fields the recovery phrase's words are typed back into suggests the
+words of BIP-39's English list that begin with what is typed (at most five, from the
+first letter; none once a whole word is typed that no longer one begins with), and
+takes no word that isn't on the list: as its field is left, it says so and keeps the
+focus there, and the words aren't handed on until every field holds one of the list's.
+A typo is so caught before the words are compared, and told apart from a wrong word.
+The suggestions come from the whole list of 2,048, never the phrase's 24, which would
+tell which words it holds; the keyboard still learns and suggests nothing.
+`isPhraseWord` and `phraseWordsBeginning` (halkyon_app's `phrase_check.dart`) decide,
+`PhraseCheckFields` shows them, on sign-up, on a new phrase and on SimpleLogin's
+sign-up alike.
+
 ## Consequences
 
 - People keep a password, an authenticator app and a recovery phrase: more to keep than a