Compact gift links: base32 codec + uppercase /g/ path for a smaller QR

Gift links now carry a compact binary encoding of just the claim-essential data
(presigned inputs + the committed change output) instead of a full PSBT (~25%
fewer bytes), base32-encoded and served at an uppercase /g/<code> path. The QR
renders the uppercase URL in the QR alphanumeric mode (5.5 bits/char vs byte
mode's 8), so the grid drops from ~73 to ~53 modules — much easier to scan.

- wallet: _encodeCompactGift/_decodeCompactGift + _giftTx dispatcher; legacy
  base64url-PSBT links still claim (auto-detected by a magic byte). Verified
  round-trip + claim-byte-identical across 1/2/3-input and whole-balance gifts,
  against the real exported preview/claim/outpoint functions.
- app: giftUrl uses /g/<code>; opener parses /g/ (and legacy #gift=); QR uses
  uppercase + Alphanumeric mode (qrSvg gains a mode option w/ byte fallback).
- nginx already SPA-routes /g/*; the SW serves the shell for the new path.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

1 files changed, 14 insertions, 4 deletions

diff --git a/src/qr.js b/src/qr.js
index fe49a02..d02aed3 100644
--- a/src/qr.js
+++ b/src/qr.js
@@ -6,10 +6,20 @@ import qrcode from 'qrcode-generator';
 // ec: error-correction level. 'M' by default; pass 'L' for long payloads (e.g.
 // gift links) where a smaller, chunkier grid scans more easily — on-screen QRs
 // are scanned immediately and don't need the damage tolerance of higher levels.
-export function qrSvg(text, { margin = 2, ec = 'M' } = {}) {
-  const qr = qrcode(0, ec); // type 0 = auto-size
-  qr.addData(text);
-  qr.make();
+// mode: pass 'Alphanumeric' for an all-uppercase QR-alphanumeric string (0-9 A-Z
+// space $%*+-./:) to pack it at 5.5 bits/char instead of byte mode's 8 — a much
+// smaller grid for the same data. Falls back to byte mode if the text doesn't fit.
+export function qrSvg(text, { margin = 2, ec = 'M', mode } = {}) {
+  let qr;
+  try {
+    qr = qrcode(0, ec);
+    qr.addData(text, mode);
+    qr.make();
+  } catch {
+    qr = qrcode(0, ec); // mode mismatch (e.g. a non-alphanumeric char) — plain byte mode
+    qr.addData(text);
+    qr.make();
+  }
 
   const count = qr.getModuleCount();
   const size = count + margin * 2;