Background: In my area, people extend their conference paper to a journal version by adding only 30% contribution. This means that you get a second paper, with the same content (introduction, related works, motivation, etc). Secondly, the order of authors matter in my area.
Story: I published a conference paper, which is one of major contributions to my PhD, and I planned to prepare an extension of that paper to be submitted to a journal. However, I postpone the extension, as I was busy with my other projects (also related to my PhD). Recently, my supervisor has secretly given the (almost) extended paper to another person to do the extension and has submitted it with a different order of names.
My supervisor and the person who extended the paper did not tell me anything about it and kept everything secret, until the last minute of submission. Although my supervisor knew that I had planned to do the extension, he ignored all my previous efforts. He even sent my already extended version to this person. However, I should acknowledge that both of them had minor contributions to the initial paper, but I am not sure if that gives them the right to extend it.
The question is whether my supervisor had the right to do so? He knew that I have planned to do the extension (as I had already extended some parts of it --I added 4-5 pages of a proof of a theorem and extended experiments).