Add QR scanner to the send page (lazy-loaded decoder)

Scan a Bitcoin address, a BIP21 URI (fills address + amount), or a
signed-transaction QR (opens a broadcast confirmation, then relays it)
from a viewfinder button on the Send form.

Decoder strategy keeps the main bundle small:
- Prefer the native BarcodeDetector (Chrome desktop/Android) — no lib.
- Otherwise lazy-load jsQR from a separate dist/jsqr.js, only when the
  scanner is opened. jsQR stays out of index.html (~424 KB vs ~551 KB)
  and off the initial load.
- The service worker precaches jsqr.js so offline scanning works for
  installed PWAs on browsers without BarcodeDetector.

The scanner needs a camera + secure context, so it never shows on a
standalone file:// page; offline air-gapped signing is unaffected.

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

1 files changed, 19 insertions, 0 deletions

diff --git a/src/wallet.js b/src/wallet.js
index 7152d31..2547b45 100644
--- a/src/wallet.js
+++ b/src/wallet.js
@@ -577,6 +577,25 @@ export class Wallet {
     return this.api.broadcast(hexTx);
   }
 
+  // Parse a raw (signed) transaction hex — used by scan-to-broadcast to show a
+  // confirmation (txid + outputs) before relaying someone's exported tx.
+  parseRawTx(rawHex) {
+    const tx = btc.Transaction.fromRaw(hex.decode(rawHex.trim()), { allowUnknownOutputs: true });
+    const network = NETS[this.netName].net;
+    const outputs = [];
+    let total = 0;
+    for (let i = 0; i < tx.outputsLength; i++) {
+      const o = tx.getOutput(i);
+      total += Number(o.amount);
+      let address = '';
+      try {
+        address = btc.Address(network).encode(btc.OutScript.decode(o.script));
+      } catch {}
+      outputs.push({ address, value: Number(o.amount) });
+    }
+    return { txid: tx.id, total, outputs };
+  }
+
   // --- realtime (mempool.space WebSocket) ---------------------------------
   // Pushes us new mempool/confirmed transactions for our addresses so history
   // and balances update with no polling.