assertEquals((byte) 0x55, dst[i], "Unexpected change after copy region at " + i);
        }
    }

    @Test
    @DisplayName("encode() with zero length does not modify destination")
    void encodeZeroLengthDoesNotModifyDestination() {
        byte[] src = makeSeq(10);
        Encodable enc = new ByteEncodable(src, 5, 0); // zero length
        byte[] dst = new byte[8];
        Arrays.fill(dst, (byte) 0x7A);