sattle: Quasar PWA scaffold with lnurlcash-kit protocol core

M1: Quasar 2 / Vue 3 / TS / Pinia / i18n / PWA app shell in the lnurl-wallet
palette (#002222/#004444/#55ffcc, Noto Sans). Protocol layer is the external
lnurlcash-kit library (git dependency on the fork until upstream merges the
prepare fix / publishes to npm); keys.ts + receive.ts vendored from
lnurl-wallet with the derivation domain renamed to 'sattle'. Nix dev shell,
ci workflow (typecheck, vitest, pwa build).

src/lnurlcash/receive.ts

@@ -0,0 +1,82 @@
+import {
+  resolveNoteInput,
+  noteK1,
+  noteDeclaredAmount,
+  serverOf,
+  fetchNoteInfo,
+  rotateNote,
+  withNewK1,
+  NoteSpentError,
+  NoteUnknownError
+} from 'lnurlcash-kit'
+import type {Bearer, NewBearer} from './types'
+
+// shared by Scan and Paste: resolve whatever came in to a note URL, ask the
+// issuing service what it is worth (an informational GET - per spec this
+// always puts k1 on the wire, so receive.ts's caller should rotate right
+// after, see secureReceivedNote). Returns the note even when the info fetch
+// fails - a bearer is better stored unverified than dropped.
+export const receiveNote = async (
+  input: string,
+  existing: Bearer[]
+): Promise<NewBearer> => {
+  const url = resolveNoteInput(input)
+  if (!url) {
+    throw new Error('Not an LNURLcash bearer note (needs a k1).')
+  }
+  const k1 = noteK1(url)
+  if (
+    existing.some(
+      b => noteK1(b.url) === k1 && serverOf(b.url) === serverOf(url)
+    )
+  ) {
+    throw new Error('This note is already in your wallet.')
+  }
+  try {
+    const info = await fetchNoteInfo(url)
+    return {
+      url,
+      callback: info.callback,
+      amount: info.maxWithdrawable,
+      verified: true,
+      mintPubkey: info.mintPubkey
+    }
+  } catch (err) {
+    // the service positively told us this k1 is dead - that's worth more
+    // than the sender's own claim, so don't paper over it with an
+    // unverified fallback the way an unreachable/unknown-shaped error
+    // below does. The caller (ReceiveDialog.tsx) surfaces this and never stores
+    // the note.
+    if (err instanceof NoteSpentError || err instanceof NoteUnknownError) {
+      throw err
+    }
+    // service unreachable (or some other non-definitive failure) - fall
+    // back to the sender's own (unverified) declared amount so the note
+    // isn't shown as worth nothing
+    return {
+      url,
+      callback: '',
+      amount: noteDeclaredAmount(url) ?? 0,
+      verified: false
+    }
+  }
+}
+
+// After receiving a note, rotate it: the previous holder (and anything that
+// logged the URL in transit, since the informational GET above already put
+// k1 on the wire) still knows the old secret - a rotate burns it and mints
+// a fresh one only this wallet knows. Returns the updated note URL. Throws
+// when the service refuses (e.g. a plain LUD-03 withdraw link that doesn't
+// speak lnurlcash) - the caller should warn, not fail the receive.
+export const secureReceivedNote = async (note: {
+  url: string
+  callback: string
+  amount: number
+}): Promise<string> => {
+  const k1 = noteK1(note.url)
+  if (!k1 || !note.callback) {
+    throw new Error('Note has no callback to rotate against yet.')
+  }
+  const result = await rotateNote(note.callback, k1)
+  return withNewK1(note.url, result.k1, note.amount, result.signature)
+}