spec: add EAGLE3 speculative decoding support (#18039)

* llama : enable layer input extraction

* spec: support eagle3

* eagle3: fix params bug

* eagle3: support Gemma4 eagle3 from RedHatAI

* eagle3: set sync when get features from target

Co-authored-by: tnhnyzc <115956684+tnhnyzc@users.noreply.github.com>

* eagle3 : fix ubatch handling in embd_layer_inp extraction and encoder

Co-authored-by: Doğaç Eldenk <dogacel@gmail.com>

* eagle3: adapt to upstream changes

* eagle3: fix rebase issues and adapt to upstream changes

* eagle3:exclude the eagle3 arch from test-llama-archs

* eagle3: fix editorconfig check failures

* eagle3: fix multi-seq issue in d2t vocab mapping

* cont : minor style / clean-up

* spec : remove `common_speculative_setup_draft_model()`

* llama : clean-up unused API

* eagle3: set d2t vocab mapping in decode graph

* cont : assert layer inputs are configured

* hparams : use n_embd_inp instead of n_embd_target_features

* eagle3: make output.weight optional and inherit from target model when needed

* haparams : generic norm-before-residual param

* llama-ext : consistent names

* cont : fix

* hparams : remove target_hidden_size

* cparams : rename output_layer_inp -> embeddings_layer_inp

* arch : reuse ATTN_NORM_2 instead of adding new hidden norm

* llama : clean-up names

* cont : add assert + comment

* Update conversion/llama.py

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
Co-authored-by: tnhnyzc <115956684+tnhnyzc@users.noreply.github.com>
Co-authored-by: Doğaç Eldenk <dogacel@gmail.com>
Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

src/llama-context.h

@@ -88,6 +88,8 @@ struct llama_context {
     float * get_embeddings_nextn();
     float * get_embeddings_nextn_ith(int32_t i);
 
+    float * get_embeddings_layer_inp(uint32_t lid);
+
     llama_token * get_sampled_tokens() const;
     llama_token   get_sampled_token_ith(int32_t idx);
 
@@ -112,6 +114,7 @@ struct llama_context {
 
     void set_embeddings (bool value);
     void set_embeddings_nextn(bool value, bool masked);
+    void set_embeddings_layer_inp(uint32_t lid, bool enable);
     void set_causal_attn(bool value);
     void set_warmup(bool value);
 
@@ -226,6 +229,10 @@ private:
     // map the output row index `i` to batch index
     int64_t output_resolve_row(int32_t i) const;
 
+    // async-copy enabled layer-input tensors (per cparams.output_layer_inp)
+    // from backend into host-side embd_layer_inp buffers
+    void extract_layer_inputs(const llm_graph_result * res, size_t token_offset, size_t n_tokens);
+
     //
     // graph
     //
@@ -288,6 +295,10 @@ private:
     // sets llm_graph_result::t_h_nextn
     buffer_view<float> embd_nextn = {nullptr, 0};
 
+    // host buffers for output layer input embeddings, per layer
+    // populated when cparams.output_layer_inp[il] is true
+    std::vector<buffer_view<float>> embd_layer_inp;
+
     struct sampling_info {
         // !samplers.empty() to check if any samplers are active
         std::map<llama_seq_id, llama_sampler *> samplers;