LlamaSession gains append_image_embeddings: precomputed vision embeddings
prefill through a second Embeddings-input graph spec sharing the same
cache tensors (SessionGraphParams grows an embeddings_input discriminant).
HybridDecodeBatchLayout gains an optional pre-expanded rope_positions
override, threaded to encode_rope_positions — cache indices and attention
masks stay linear while image tokens get qwen-vl 2D positions
[pos0, pos0+y, pos0+x, 0] and the span advances rope position by
max(w, h). Text after an image continues from the shifted position; pure
text paths are byte-identical to before (verified via llama-generate).
vlm-probe runs the whole thing: ppm -> vision tower -> chatml with
vision_start/end -> greedy. Output is token-for-token identical to
llama-mtmd-cli --temp 0 on both test images (radar scene description and
'A red circle.'). 229-token mixed prefill 0.98s, generation 27.9 tok/s
on the 9B UD-Q4_K_XL.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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