Shoe rec for a self-supported 180k cross-Alps run

The goal

I'm training for a fully self-supported ~180k multi-day traverse across the Austrian Alps, roughly 60km/day and 3000-4000m of elevation gain and loss per day. I wanted to do bigger days, but I'm not willing to run technical high-alpine terrain in the dark, so I'm capping daily distance to stay in daylight.

Terrain

The full spectrum: runnable, buffed trail all the way to very steep, technical alpine, up to ~3300m. So I'm after shoes that can handle the distance as well as the different terrains well.

Current shoe + the problem

I'm in the Brooks Cascadia Elite. On the uphills it's hands down the best trail shoe I've ever run in. The descents are the problem: I get shredded with blisters on the outside of my big toe and the inside of my heel, on both feet. It feels like my foot is sliding around inside the shoe on the downhills even though I run a proper heel lock and try to lock the midfoot down too. Climbing is perfect, descending is wrecking my feet. Note I already use Injinji toe socks and another setup with the Injinji liners + running socks.

What I'm looking for

A shoe — or a fit/lacing fix — that actually holds my foot on steep technical descents without giving up the climbing performance and comfort the Cascadia has. Bonus points if it holds up to multi-day back-to-back abuse.

If you run similar terrain and distances: what's keeping your foot locked down on long alpine descents? Looking for specific models, last/width notes, and any lacing tricks that worked for you.

Happy for any feedback and inputs you might have.