**Likely Root Cause:** 
Insufficient GPU VRAM to allocate the KV cache for the requested 256K context length. A 262,144-token context requires multiple gigabytes (often 10–30+ GB depending on model size) just for the KV cache, but only 1,024 MiB (1 GB) is currently free on the GPU.

**Next Two Actions:**
1. Reduce the context size to fit available VRAM by launching with `--ctx-size <N>` (e.g., `--ctx-size 8192` or `16384`).
2. Decrease GPU layer offloading using `--gpu-layers <N>` (or `--ngl`) to reserve more VRAM for the KV cache, or run `nvidia-smi` to identify and terminate other GPU memory consumers.