spec: support eagle3 for qwen3.5 & 3.6 (#24593)

* spec: support qwen3.5 & 3.6 eagle3 draft

* eagle3: Add deferred boundary checkpoints restore support for hybrid models

* apply suggestions

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

* spec: adapt to API change

* spec: fix naming

* cont : add TODO

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

common/common.cpp

@@ -2034,7 +2034,7 @@ bool common_prompt_batch_decode(
 }
 
 size_t common_prompt_checkpoint::size() const {
-    return data_tgt.size() + data_dft.size();
+    return data_tgt.size() + data_dft.size() + data_spec.size();
 }
 
 bool common_prompt_checkpoint::empty() const {
@@ -2049,6 +2049,7 @@ void common_prompt_checkpoint::clear() {
 
     data_tgt.clear();
     data_dft.clear();
+    data_spec.clear();
 }
 
 void common_prompt_checkpoint::update_pos(
@@ -2138,4 +2139,5 @@ void common_prompt_checkpoint::clear_tgt() {
 
 void common_prompt_checkpoint::clear_dft() {
     data_dft.clear();
+    data_spec.clear();
 }

common/common.h

@@ -363,7 +363,7 @@ struct common_params_speculative {
 
     uint32_t need_n_rs_seq() const {
         bool needs_rs_seq = std::any_of(types.begin(), types.end(), [&](auto t) {
-            return t == COMMON_SPECULATIVE_TYPE_DRAFT_MTP;
+            return t == COMMON_SPECULATIVE_TYPE_DRAFT_MTP || t == COMMON_SPECULATIVE_TYPE_DRAFT_EAGLE3;
         });
 
         return needs_rs_seq ? draft.n_max : 0u;
@@ -1065,6 +1065,10 @@ struct common_prompt_checkpoint {
     std::vector<uint8_t> data_tgt;
     std::vector<uint8_t> data_dft;
 
+    // (optional) speculative-decoding implementation state stashed with the checkpoint
+    // (e.g. eagle3's deferred-boundary g_embd row)
+    std::vector<uint8_t> data_spec;
+
     size_t size() const;
 
     bool empty() const;

common/speculative.cpp

@@ -161,6 +161,10 @@ struct common_speculative_impl {
 
     virtual void accept(llama_seq_id seq_id, uint16_t n_accepted, bool is_other) = 0;
 
+    // (optional) serialize/restore per-seq internal state (e.g. eagle3's deferred boundary).
+    virtual bool get_state(llama_seq_id /*seq_id*/, std::vector<uint8_t> & /*data*/) const { return false; }
+    virtual void set_state(llama_seq_id /*seq_id*/, const std::vector<uint8_t> & /*data*/) {}
+
     // true if this implementation requires the target context to extract post-norm embeddings
     virtual bool need_embd() const = 0;
 
@@ -841,6 +845,49 @@ struct common_speculative_impl_draft_eagle3 : public common_speculative_impl {
                     (size_t) n_embd_dec * sizeof(float));
     }
 
+    // we only need to stash the deferred boundary's g_embd row for recurrent/hybrid targets:
+    // their single-position checkpoints drop it on restore
+    bool need_boundary_stash() const {
+        const llama_model * model_tgt = llama_get_model(params.ctx_tgt);
+        return llama_model_is_recurrent(model_tgt) || llama_model_is_hybrid(model_tgt);
+    }
+
+    bool get_state(llama_seq_id seq_id, std::vector<uint8_t> & data) const override {
+        if (!need_boundary_stash()) {
+            return false;
+        }
+        if (seq_id < 0 || seq_id >= (llama_seq_id) n_seq || pending_pos_last[seq_id] < 0) {
+            return false;
+        }
+
+        const llama_pos          pos = pending_pos_last[seq_id];
+        const std::vector<float> & g = pending_g_last[seq_id];
+
+        data.resize(sizeof(llama_pos) + g.size() * sizeof(float));
+        std::memcpy(data.data(),                     &pos,     sizeof(llama_pos));
+        std::memcpy(data.data() + sizeof(llama_pos), g.data(), g.size() * sizeof(float));
+        return true;
+    }
+
+    void set_state(llama_seq_id seq_id, const std::vector<uint8_t> & data) override {
+        if (!need_boundary_stash()) {
+            return;
+        }
+        if (seq_id < 0 || seq_id >= (llama_seq_id) n_seq) {
+            return;
+        }
+        if (data.size() != sizeof(llama_pos) + (size_t) n_embd_dec * sizeof(float)) {
+            return;
+        }
+
+        llama_pos pos = -1;
+        std::memcpy(&pos, data.data(), sizeof(llama_pos));
+
+        pending_pos_last[seq_id] = pos;
+        pending_g_last[seq_id].resize(n_embd_dec);
+        std::memcpy(pending_g_last[seq_id].data(), data.data() + sizeof(llama_pos), (size_t) n_embd_dec * sizeof(float));
+    }
+
     bool need_embd() const override {
         return false;
     }
@@ -2118,6 +2165,31 @@ void common_speculative_accept(common_speculative * spec, llama_seq_id seq_id, u
     }
 }
 
+// TODO: support the case of more than one speculative implementations having a state
+bool common_speculative_get_state(common_speculative * spec, llama_seq_id seq_id, std::vector<uint8_t> & data) {
+    if (spec == nullptr) {
+        return false;
+    }
+
+    for (auto & impl : spec->impls) {
+        if (impl->get_state(seq_id, data)) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
+void common_speculative_set_state(common_speculative * spec, llama_seq_id seq_id, const std::vector<uint8_t> & data) {
+    if (spec == nullptr) {
+        return;
+    }
+
+    for (auto & impl : spec->impls) {
+        impl->set_state(seq_id, data);
+    }
+}
+
 void common_speculative_print_stats(const common_speculative * spec) {
     if (spec == nullptr) {
         return;

common/speculative.h

@@ -68,6 +68,10 @@ void common_speculative_draft(common_speculative * spec);
 // informs the speculative context that n_accepted tokens were accepted by the target model
 void common_speculative_accept(common_speculative * spec, llama_seq_id, uint16_t n_accepted);
 
+// (optional) get/set internal state
+bool common_speculative_get_state(common_speculative * spec, llama_seq_id seq_id, std::vector<uint8_t> & data);
+void common_speculative_set_state(common_speculative * spec, llama_seq_id seq_id, const std::vector<uint8_t> & data);
+
 // print statistics about the speculative decoding
 void common_speculative_print_stats(const common_speculative * spec);