feat(core-go): implement uint64 extraction from muxed address in Deco…

packages/core-go/muxed/decode.go

@@ -1,22 +1,54 @@
 package muxed
 
 import (
-	"encoding/binary"
-	"fmt"
+ "encoding/binary"
 
-	"github.com/stellar-address-kit/core-go/address"
+ "github.com/stellar-address-kit/core-go/address"
 )
 
-func DecodeMuxed(mAddress string) (string, string, error) {
-	muxedAccount, err := strkey.DecodeMuxedAccount(mAddress)
-	if err != nil {
-		return "", "", err
-	}
+// DecodeMuxed extracts the base G-address and uint64 ID from a muxed
+// M-address. The 64-bit ID is parsed directly from the big-endian payload
+// using binary.BigEndian.Uint64, matching the Stellar protocol's native
+// byte-aligned serialization.
+func DecodeMuxed(mAddress string) (string, uint64, error) {
+ versionByte, payload, err := address.DecodeStrKey(mAddress)
+ if err != nil {
+  return "", 0, &AddressError{
+   Code:    ErrInvalidGAddress,
+   Input:   mAddress,
+   Message: "failed to decode muxed address",
+   Cause:   err,
+  }
+ }
 
-	baseG, err := muxedAccount.AccountID()
-	if err != nil {
-		return "", 0, err
-	}
+ if versionByte != address.VersionByteMuxedAccount {
+  return "", 0, &AddressError{
+   Code:    ErrUnknownVersionByte,
+   Input:   mAddress,
+   Message: "expected muxed account version byte",
+  }
+ }
 
-	return baseG, strconv.FormatUint(muxedAccount.ID(), 10), nil
-}
+ if len(payload) != 40 {
+  return "", 0, &AddressError{
+   Code:    ErrInvalidLength,
+   Input:   mAddress,
+   Message: "muxed payload must be 40 bytes",
+  }
+ }
+
+ pubkey := payload[:32]
+ id := binary.BigEndian.Uint64(payload[32:40])
+
+ baseG, err := address.EncodeStrKey(address.VersionByteAccountID, pubkey)
+ if err != nil {
+  return "", 0, &AddressError{
+   Code:    ErrInvalidGAddress,
+   Input:   mAddress,
+   Message: "failed to encode base G-address",
+   Cause:   err,
+  }
+ }
+
+ return baseG, id, nil
+}