How to renew scientist visa for a PhD extension?

Question

I have been on a scientist visa in France for about 2.5 years. I am supposed to finish my PhD in October, and my visa expires on the last day of September.

I have already received the green light to get an extra 3 months of funding (through January), and I suppose I should be extending my residence permit sometime in July. At that time, I will not have my defense set up (I still have to produce my manuscript). How do I extend my visa / TDS for a few months?

I asked at my lab, and I was told that it can take up to a year to renew a visa in my préfecture, during which time I won't be able to leave France. If it takes a year to renew a French residence permit, and I only need a 3 month extension, what is the best course of action here?

I need to be able to stay in France until potentially the beginning of February. After I submit and defend my thesis, I will be applying for a visa in an asian country for a postdoc. I cannot apply for that visa until I have my diploma in hand, and I cannot stay past my defense under my current visa situation. It would be rather silly to move back to my home country (non-EU and where I haven't lived in a decade) to do that. I would also like to avoid that for personal reasons.

If it makes any difference, I am pacsé with a French national and we're considering getting married before I have to leave. We live together. I'm not sure if that makes any difference with this whole thing. I didn't really intend to go the spouse visa route until after my 3 years outside Europe was finished (especially since we will be long distance for 3 years) but I'm willing to consider it if it makes the situation any easier.

To make matters worse, I submitted a change of address (requesting a new titre de sejour) only last week (at a different prefecture), and I have no idea how long that will take, or if it will invalidate the residence permit I already have.

Answer 1

As the "pacs" of a French national, you can apply for a carte de séjour vie privée et familiale:

Le Pacs conclu par un étranger non européen avec un Français, un Européen ou un autre étranger permet également la délivrance d'une carte vie privée et familiale.

A Pacs concluded by a non-EU foreigner with a French citizen, a European, or another foreigner equally permits the issue of a carte vie privée et familiale.

The page for the Carte de séjour "vie privée et familiale" contains information about applying if you are married to a French citizen.

Whether you apply for that or apply to renew your current status, it seems like you should file the application and then leave when you are ready to abandon it. For the restriction is not that you literally are forbidden to leave France while the application is pending, but that leaving France constitutes abandonment of the application. After you leave and abandon the application, you can still return with your non-EU passport for short visits subject to the 90/180 rule (if I recall correctly, you are from an Annex II country, so you will not need a visa).