Qwen3-VL hits Vulkan inference friction

Qwen3-VL may be broadly supported in llama.cpp now, but “supported” still does not mean painless across every GPU backend.

• –Vulkan remains a rougher path than CUDA or Metal for multimodal workloads, especially on edge cases involving vision encoders.
• –Empty captions usually suggest the vision side is not actually being wired in, often because the mmproj file is missing, mismatched, or not loaded correctly.
• –Qwen2.5-VL failing too makes this look less like a single-model issue and more like a local setup, prompt format, or backend support problem.
• –For developers, the practical test is simple: verify the same model and mmproj on CPU or CUDA first, then isolate Vulkan-specific failures.