fix(chain): support Taproot (bech32m/BIP350) in BtcAddress validation + scriptPubKey

BtcAddress::bech32Verify only checked the bech32 (BIP173) checksum
constant (=== 1), so valid Taproot addresses (bc1p, witness v1,
bech32m, const 0x2bc830a3) failed checksum verification and were
rejected as 'Invalid to address' by TransferService.

- bech32Verify now returns the detected encoding ('bech32' | 'bech32m' | null)
- decodeBech32 enforces BIP350 version<->encoding consistency
  (v0 must be bech32, v1+ must be bech32m)
- scriptPubKey adds the P2TR (v1 + 32-byte) branch: OP_1 <32> = 5120...
- bech32Checksum/bech32Encode pick the correct constant per witness
  version so Taproot encoding round-trips correctly

Co-authored-by: Cursor <cursoragent@cursor.com>

app/Services/Chain/BtcAddress.php

@@ -92,6 +92,10 @@ final class BtcAddress
             if ($ver === 0 && strlen($prog) === 32) {
                 return ['type' => 'p2wsh', 'script' => '0020'.bin2hex($prog)];
             }
+            if ($ver === 1 && strlen($prog) === 32) {
+                // Taproot (BIP341): OP_1 <32>
+                return ['type' => 'p2tr', 'script' => '5120'.bin2hex($prog)];
+            }
             throw new RuntimeException('Unsupported bech32 witness program');
         }
 
@@ -163,7 +167,8 @@ final class BtcAddress
         if (count($values) < 7) {
             throw new RuntimeException('Invalid bech32 length');
         }
-        if (! self::bech32Verify($hrp, $values)) {
+        $spec = self::bech32Verify($hrp, $values);
+        if ($spec === null) {
             throw new RuntimeException('Invalid bech32 checksum');
         }
         $values = array_slice($values, 0, -6);
@@ -171,6 +176,13 @@ final class BtcAddress
         if ($version > 16) {
             throw new RuntimeException('Invalid witness version');
         }
+        // BIP350: witness v0 must use bech32, v1+ must use bech32m.
+        if ($version === 0 && $spec !== 'bech32') {
+            throw new RuntimeException('Invalid bech32 checksum (v0 must be bech32)');
+        }
+        if ($version !== 0 && $spec !== 'bech32m') {
+            throw new RuntimeException('Invalid bech32m checksum (v1+ must be bech32m)');
+        }
         $program = self::convertBits(array_slice($values, 1), 5, 8, false);
         if ($program === null) {
             throw new RuntimeException('Invalid witness program');
@@ -206,7 +218,7 @@ final class BtcAddress
         for ($i = 0; $i < strlen($bits); $i += 5) {
             $values[] = bindec(substr($bits, $i, 5));
         }
-        $values = array_merge($values, self::bech32Checksum($hrp, $values));
+        $values = array_merge($values, self::bech32Checksum($hrp, $values, $witver));
         $result = $hrp.'1';
         foreach ($values as $v) {
             $result .= $charset[$v];
@@ -216,14 +228,16 @@ final class BtcAddress
     }
 
     /** @param list<int> $values */
-    private static function bech32Checksum(string $hrp, array $values): array
+    private static function bech32Checksum(string $hrp, array $values, int $witver): array
     {
+        // BIP350: v0 uses bech32 const (1), v1+ uses bech32m const (0x2bc830a3).
+        $const = $witver === 0 ? 1 : 0x2bc830a3;
         $polymod = self::bech32Polymod(array_merge(
             self::bech32HrpExpand($hrp),
             $values,
             [0, 0, 0, 0, 0, 0],
         ));
-        $polymod ^= 1;
+        $polymod ^= $const;
         $ret = [];
         for ($i = 0; $i < 6; $i++) {
             $ret[] = ($polymod >> 5 * (5 - $i)) & 31;
@@ -232,10 +246,23 @@ final class BtcAddress
         return $ret;
     }
 
-    /** @param list<int> $values */
+    /**
-    private static function bech32Verify(string $hrp, array $values): bool
+     * Detect bech32/bech32m encoding from the checksum (BIP173 / BIP350).
+     *
+     * @param  list<int>  $values
+     * @return string|null 'bech32' (v0) | 'bech32m' (v1+) | null (invalid)
+     */
+    private static function bech32Verify(string $hrp, array $values): ?string
     {
-        return self::bech32Polymod(array_merge(self::bech32HrpExpand($hrp), $values)) === 1;
+        $polymod = self::bech32Polymod(array_merge(self::bech32HrpExpand($hrp), $values));
+        if ($polymod === 1) {
+            return 'bech32';
+        }
+        if ($polymod === 0x2bc830a3) {
+            return 'bech32m';
+        }
+
+        return null;
     }
 
     /** @return list<int> */