feat(stage-8b): Llama + Qwen3 MoE families on the candle harness

Broadens the single-GPU dense and quantized paths to cover three
non-Qwen3 architectures already shipped by candle-transformers. TP for
these is a separate stage (each family would need its own tp_*.rs
mirroring tp_qwen3.rs).

`ModelArch` gains four variants:
- LlamaDense (boxed — wraps Llama + an inline Cache + the config it
  takes to rebuild the cache, since candle::llama::Cache has no reset)
- LlamaQuantized (candle_transformers::models::quantized_llama)
- Qwen3MoeDense (candle::models::qwen3_moe::ModelForCausalLM)
- Qwen3MoeQuantized (candle::models::quantized_qwen3_moe::GGUFQWenMoE
  — takes an explicit compute dtype; F16 by default for best
  consumer-GPU throughput)

The dispatch is method-based now:
- `ModelArch::forward(&mut self, input, offset) -> Result<Tensor>`
  with a shared `squeeze_to_vocab` normalising shape differences
  (qwen3 returns [B,1,V]; quantized_qwen3 returns [B,V]; new families
  may differ again — the helper handles all of them).
- `ModelArch::clear_kv_cache(&mut self) -> Result<()>`. Llama needs
  a Cache rebuild because its Cache has no in-place reset; the new
  `LlamaDense` wrapper holds the bits needed to do it.

`run_inference` / `run_inference_streaming` collapse to a single
dispatch path: no more per-variant match arms in the hot loop, and
new architectures pick up streaming + non-streaming for free with
zero changes outside `ModelArch`.

DENSE_SUPPORTED_MODEL_TYPES is now ["llama", "qwen3", "qwen3_moe"].
GGUF arch switch grows "qwen3moe" + "llama" branches (qwen3moe with
no underscore matches llama.cpp's general.architecture convention).
Stage 8a's diagnostic auto-reports the new supported set.

The `LlamaDense` variant is boxed because the wrapper's inline Cache
+ Config makes it 544 bytes vs ~300 for everything else
(clippy::large_enum_variant).

Verified: cargo test --workspace passes 66 tests; cargo clippy CPU
and `--features cuda` both clean (the cuda check ran inside the
locally-built `neuron-build-local` container with the math_functions.h
patch applied).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/neuron/src/harness/candle.rs

@@ -14,8 +14,12 @@ use candle_core::quantized::gguf_file;
 use candle_core::{DType, Device, Tensor};
 use candle_nn::VarBuilder;
 use candle_transformers::generation::{LogitsProcessor, Sampling};
+use candle_transformers::models::llama as llama_dense;
+use candle_transformers::models::quantized_llama::ModelWeights as QuantizedLlamaWeights;
 use candle_transformers::models::quantized_qwen3::ModelWeights as QuantizedQwen3Weights;
+use candle_transformers::models::quantized_qwen3_moe::GGUFQWenMoE;
 use candle_transformers::models::qwen3 as qwen3_dense;
+use candle_transformers::models::qwen3_moe as qwen3_moe_dense;
 use cortex_core::harness::{Harness, HarnessHealth, ModelInfo, ModelSpec};
 use cortex_core::openai::{
     ChatCompletionChoice, ChatCompletionChunk, ChatCompletionRequest, ChatCompletionResponse,
@@ -100,21 +104,109 @@ pub struct TpLoadedModel {
     pub leader_model: Arc<tokio::sync::Mutex<super::tp::tp_qwen3::TpQwen3ForCausalLM>>,
 }
 
-/// Architecture-specific weights.
+/// Architecture-specific weights. Each variant covers one (family,
+/// source-format) pair; the dense variants take the safetensors path
+/// and the `Quantized*` variants take the GGUF path.
 ///
-/// - `Qwen3Quantized` — GGUF source, pre-quantized. Single-GPU only;
-///   TP sharding pre-quantized super-blocks is intractable. Stays the
-///   default for small models loaded via `Qwen/Qwen3-*-GGUF` and
-///   `unsloth/Qwen3-*-GGUF` repos.
-/// - `Qwen3Dense` — bf16 safetensors source. The path that supports
-///   TP (Stage 7b-ii+) because slicing dense weights by row/column
-///   under safetensors is mechanical. Used when `ModelSpec.quant` is
-///   None; intended target for Qwen3.6-27B etc.
-///
-/// Stage 8 broadens this to additional families.
+/// TP currently only works through `Qwen3Dense` (see `tp_qwen3.rs`);
+/// every other variant is single-GPU. Quantized variants can't shard
+/// across GPUs at all — slicing GGUF super-blocks is intractable —
+/// and the new dense families (Llama, Qwen3 MoE) lack their own
+/// TP-aware modules yet.
 pub enum ModelArch {
+    // Qwen3 family
     Qwen3Quantized(QuantizedQwen3Weights),
     Qwen3Dense(qwen3_dense::ModelForCausalLM),
+    Qwen3MoeQuantized(GGUFQWenMoE),
+    Qwen3MoeDense(qwen3_moe_dense::ModelForCausalLM),
+
+    // Llama family (covers Llama 1/2/3/3.1/3.3). Boxed because the
+    // wrapper carries an inline Cache + Config — without indirection
+    // the enum's `LlamaDense` variant is several hundred bytes larger
+    // than the others (clippy::large_enum_variant).
+    LlamaQuantized(QuantizedLlamaWeights),
+    LlamaDense(Box<LlamaDense>),
+}
+
+impl ModelArch {
+    /// One forward step on this arch with the rank-1 vocab logits
+    /// extracted. Hides per-family shape differences (some return
+    /// `[B, V]`, others `[B, 1, V]`) — every caller gets a `[V]`
+    /// tensor ready for sampling.
+    pub fn forward(&mut self, input: &Tensor, offset: usize) -> Result<Tensor> {
+        let raw = match self {
+            ModelArch::Qwen3Quantized(m) => m.forward(input, offset)?,
+            ModelArch::Qwen3Dense(m) => m.forward(input, offset)?,
+            ModelArch::Qwen3MoeQuantized(m) => m.forward(input, offset)?,
+            ModelArch::Qwen3MoeDense(m) => m.forward(input, offset)?,
+            ModelArch::LlamaQuantized(m) => m.forward(input, offset)?,
+            ModelArch::LlamaDense(m) => m.forward(input, offset)?,
+        };
+        squeeze_to_vocab(&raw)
+    }
+
+    /// Reset the KV cache before each new request so we don't attend
+    /// over a previous request's tokens. Some architectures have an
+    /// in-place reset; Llama needs a Cache rebuild (held inline in
+    /// the wrapper).
+    pub fn clear_kv_cache(&mut self) -> Result<()> {
+        match self {
+            ModelArch::Qwen3Quantized(_) => Ok(()), /* keeps cache by design;
+            * forward() handles offset */
+            ModelArch::Qwen3Dense(m) => {
+                m.clear_kv_cache();
+                Ok(())
+            }
+            ModelArch::Qwen3MoeQuantized(_) => Ok(()),
+            ModelArch::Qwen3MoeDense(m) => {
+                m.clear_kv_cache();
+                Ok(())
+            }
+            ModelArch::LlamaQuantized(_) => Ok(()),
+            ModelArch::LlamaDense(m) => m.clear_kv_cache(),
+        }
+    }
+}
+
+/// Squeeze any leading singleton dims off the logits tensor so the
+/// caller gets a rank-1 `[vocab_size]` slice ready for sampling. Bails
+/// on a non-singleton leading dim (would mean a batched forward, which
+/// no caller emits today).
+fn squeeze_to_vocab(t: &Tensor) -> Result<Tensor> {
+    let mut t = t.clone();
+    while t.dims().len() > 1 {
+        if t.dims()[0] != 1 {
+            anyhow::bail!(
+                "logits expected to start with a singleton dim, got shape {:?}",
+                t.dims()
+            );
+        }
+        t = t.squeeze(0)?;
+    }
+    Ok(t)
+}
+
+/// Llama dense wrapper. Bundles candle's `Llama` model with its
+/// externally-managed `Cache` plus enough config to rebuild the
+/// cache on `clear_kv_cache` (Llama's Cache doesn't expose a reset).
+pub struct LlamaDense {
+    model: llama_dense::Llama,
+    cache: llama_dense::Cache,
+    config: llama_dense::Config,
+    dtype: DType,
+    device: Device,
+}
+
+impl LlamaDense {
+    pub fn forward(&mut self, input: &Tensor, offset: usize) -> Result<Tensor> {
+        Ok(self.model.forward(input, offset, &mut self.cache)?)
+    }
+
+    pub fn clear_kv_cache(&mut self) -> Result<()> {
+        self.cache = llama_dense::Cache::new(true, self.dtype, &self.config, &self.device)
+            .context("rebuild Llama Cache for new request")?;
+        Ok(())
+    }
 }
 
 /// Repetition penalty applied to recently-generated tokens before
@@ -130,11 +222,10 @@ const REPEAT_LAST_N: usize = 64;
 
 /// Architectures the dense safetensors path can construct. Keep
 /// alphabetical; one entry per supported `config.json#/model_type`
-/// value. New entries land alongside a new `ModelArch` variant + a new
-/// dispatch branch in `load_arch_dense` / `run_inference` /
-/// `run_inference_streaming` (plus, for TP, a parallel pattern in
-/// `tp_qwen3.rs`).
-const DENSE_SUPPORTED_MODEL_TYPES: &[&str] = &["qwen3"];
+/// value. New entries land alongside a new `ModelArch` variant + a
+/// dispatch branch in `load_arch_dense` (plus, for TP, a parallel
+/// pattern in `tp_qwen3.rs`).
+const DENSE_SUPPORTED_MODEL_TYPES: &[&str] = &["llama", "qwen3", "qwen3_moe"];
 
 /// Pre-flight check the operator's `config.json` against the set of
 /// architectures the dense path actually knows how to build. Surfaces
@@ -362,6 +453,9 @@ impl CandleHarness {
                 .unwrap_or_default();
             tracing::info!(architecture = %architecture, "GGUF architecture");
 
+            // The `general.architecture` GGUF metadata key follows
+            // llama.cpp conventions (lowercase, no underscores in some
+            // cases) — `qwen3moe`, not `qwen3_moe`.
             match architecture.as_str() {
                 "qwen3" => {
                     let weights =
@@ -369,8 +463,25 @@ impl CandleHarness {
                             .map_err(|e| anyhow::anyhow!("from_gguf qwen3: {e}"))?;
                     Ok(ModelArch::Qwen3Quantized(weights))
                 }
+                "qwen3moe" => {
+                    // GGUFQWenMoE takes an explicit compute dtype
+                    // alongside the device — F16 matches the GGUF
+                    // weights' typical accumulation precision and
+                    // gives the best tokens/sec on consumer cards.
+                    let weights =
+                        GGUFQWenMoE::from_gguf(content, &mut file, &device_for_load, DType::F16)
+                            .map_err(|e| anyhow::anyhow!("from_gguf qwen3_moe: {e}"))?;
+                    Ok(ModelArch::Qwen3MoeQuantized(weights))
+                }
+                "llama" => {
+                    let weights =
+                        QuantizedLlamaWeights::from_gguf(content, &mut file, &device_for_load)
+                            .map_err(|e| anyhow::anyhow!("from_gguf llama: {e}"))?;
+                    Ok(ModelArch::LlamaQuantized(weights))
+                }
                 other => anyhow::bail!(
-                    "unsupported GGUF architecture '{other}'; quantized path only supports qwen3"
+                    "unsupported GGUF architecture '{other}'; quantized path supports \
+                     qwen3, qwen3moe, llama"
                 ),
             }
         })
@@ -396,32 +507,84 @@ impl CandleHarness {
         let model_id_for_log = spec.model_id.clone();
 
         let arch = tokio::task::spawn_blocking(move || -> Result<ModelArch> {
-            tracing::info!(
-                model = %model_id_for_log,
-                shards = safetensors_paths.len(),
-                "loading dense Qwen3 from safetensors"
-            );
             let cfg_text = std::fs::read_to_string(&config_path).context("read config.json")?;
             check_dense_config_supported(&cfg_text, &model_id_for_log)?;
-            let cfg: qwen3_dense::Config =
-                serde_json::from_str(&cfg_text).context("parse Qwen3 config.json")?;
+            // Peek at model_type to choose the family before the
+            // typed deserialize — each family has its own Config.
+            let model_type = serde_json::from_str::<serde_json::Value>(&cfg_text)
+                .ok()
+                .as_ref()
+                .and_then(|v| v.get("model_type"))
+                .and_then(|v| v.as_str())
+                .unwrap_or("")
+                .to_string();
+            tracing::info!(
+                model = %model_id_for_log,
+                model_type = %model_type,
+                shards = safetensors_paths.len(),
+                "loading dense model from safetensors"
+            );
 
-            // bf16 is the canonical Qwen3 distribution dtype. CUDA
-            // devices on Ada+ support it; Ampere also supports bf16
-            // natively. CPU candle handles bf16 via emulation.
+            // bf16 is the canonical distribution dtype for Qwen3 /
+            // Llama 3 / Qwen3 MoE. CUDA on Ada+ has hardware bf16;
+            // Ampere has it too. CPU emulates.
             let dtype = DType::BF16;
             // SAFETY: VarBuilder::from_mmaped_safetensors mmaps the files;
-            // mutation of the underlying files by another process while
-            // we hold the mapping is UB. We trust that nothing else on
-            // the host modifies the HF cache files during a model's
-            // lifetime (hf-hub itself is immutable-by-design).
+            // mutation by another process while we hold the mapping is
+            // UB. We trust the HF cache is immutable-by-design.
             let vb = unsafe {
                 VarBuilder::from_mmaped_safetensors(&safetensors_paths, dtype, &device_for_load)
                     .context("build VarBuilder over safetensors")?
             };
-            let model = qwen3_dense::ModelForCausalLM::new(&cfg, vb)
-                .map_err(|e| anyhow::anyhow!("build Qwen3 dense model: {e}"))?;
-            Ok(ModelArch::Qwen3Dense(model))
+
+            match model_type.as_str() {
+                "qwen3" => {
+                    let cfg: qwen3_dense::Config =
+                        serde_json::from_str(&cfg_text).context("parse Qwen3 config.json")?;
+                    let model = qwen3_dense::ModelForCausalLM::new(&cfg, vb)
+                        .map_err(|e| anyhow::anyhow!("build Qwen3 dense model: {e}"))?;
+                    Ok(ModelArch::Qwen3Dense(model))
+                }
+                "qwen3_moe" => {
+                    let cfg: qwen3_moe_dense::Config =
+                        serde_json::from_str(&cfg_text).context("parse Qwen3 MoE config.json")?;
+                    let model = qwen3_moe_dense::ModelForCausalLM::new(&cfg, vb)
+                        .map_err(|e| anyhow::anyhow!("build Qwen3 MoE dense model: {e}"))?;
+                    Ok(ModelArch::Qwen3MoeDense(model))
+                }
+                "llama" => {
+                    let cfg: llama_dense::LlamaConfig =
+                        serde_json::from_str(&cfg_text).context("parse Llama config.json")?;
+                    // Llama has multiple sub-variants (Llama 1 has no
+                    // GQA; Llama 3 does). `LlamaConfig::into_config`
+                    // resolves the right shape; the `use_flash_attn`
+                    // arg defaults to false — the flash kernel is a
+                    // separate feature flag and uses extra VRAM.
+                    let config = cfg.into_config(false);
+                    let cache = llama_dense::Cache::new(true, dtype, &config, &device_for_load)
+                        .context("build Llama Cache")?;
+                    let model = llama_dense::Llama::load(vb, &config)
+                        .map_err(|e| anyhow::anyhow!("build Llama dense model: {e}"))?;
+                    Ok(ModelArch::LlamaDense(Box::new(LlamaDense {
+                        model,
+                        cache,
+                        config,
+                        dtype,
+                        device: device_for_load,
+                    })))
+                }
+                other => {
+                    // Defensive: `check_dense_config_supported` already
+                    // gated on the supported set, so this branch is
+                    // unreachable unless that list and the match here
+                    // drift apart.
+                    anyhow::bail!(
+                        "unrouted supported model_type '{other}' — \
+                         DENSE_SUPPORTED_MODEL_TYPES and load_arch_dense \
+                         must stay in sync"
+                    )
+                }
+            }
         })
         .await
         .context("blocking dense load task panicked")??;
@@ -1375,25 +1538,10 @@ fn run_inference(
 
     let mut generated: Vec<u32> = Vec::new();
 
-    let mut next_token = match arch {
-        ModelArch::Qwen3Quantized(model) => {
-            model.clear_kv_cache();
-            let input = Tensor::new(prompt_tokens, device)?.unsqueeze(0)?;
-            let logits = model.forward(&input, 0)?;
-            let logits = logits.squeeze(0)?;
-            sample_with_penalty(&logits, &generated, &mut logits_processor)?
-        }
-        ModelArch::Qwen3Dense(model) => {
-            model.clear_kv_cache();
-            let input = Tensor::new(prompt_tokens, device)?.unsqueeze(0)?;
-            // qwen3::ModelForCausalLM::forward returns [B, 1, V] —
-            // no final squeeze on the dense path, unlike the quantized
-            // variant which returns [B, V]. Strip both batch and seq
-            // dims to get the rank-1 logits LogitsProcessor expects.
-            let logits = model.forward(&input, 0)?.squeeze(0)?.squeeze(0)?;
-            sample_with_penalty(&logits, &generated, &mut logits_processor)?
-        }
-    };
+    arch.clear_kv_cache()?;
+    let input = Tensor::new(prompt_tokens, device)?.unsqueeze(0)?;
+    let logits = arch.forward(&input, 0)?;
+    let mut next_token = sample_with_penalty(&logits, &generated, &mut logits_processor)?;
 
     if Some(next_token) == eos_id {
         return Ok((generated, "stop".into()));
@@ -1401,23 +1549,9 @@ fn run_inference(
     generated.push(next_token);
 
     for index in 0..max_new.saturating_sub(1) {
-        next_token = match arch {
-            ModelArch::Qwen3Quantized(model) => {
-                let input = Tensor::new(&[next_token], device)?.unsqueeze(0)?;
-                let logits = model.forward(&input, prompt_tokens.len() + index)?;
-                let logits = logits.squeeze(0)?;
-                sample_with_penalty(&logits, &generated, &mut logits_processor)?
-            }
-            ModelArch::Qwen3Dense(model) => {
-                let input = Tensor::new(&[next_token], device)?.unsqueeze(0)?;
-                // Dense returns [B, 1, V]; strip both leading dims.
-                let logits = model
-                    .forward(&input, prompt_tokens.len() + index)?
-                    .squeeze(0)?
-                    .squeeze(0)?;
-                sample_with_penalty(&logits, &generated, &mut logits_processor)?
-            }
-        };
+        let input = Tensor::new(&[next_token], device)?.unsqueeze(0)?;
+        let logits = arch.forward(&input, prompt_tokens.len() + index)?;
+        next_token = sample_with_penalty(&logits, &generated, &mut logits_processor)?;
         if Some(next_token) == eos_id {
             return Ok((generated, "stop".into()));
         }
@@ -1465,22 +1599,10 @@ fn run_inference_streaming(
     let mut decoded_prefix = String::new();
     let mut finish_reason = "length".to_string();
 
-    let mut next_token = match arch {
-        ModelArch::Qwen3Quantized(model) => {
-            model.clear_kv_cache();
-            let input = Tensor::new(prompt_tokens, device)?.unsqueeze(0)?;
-            let logits = model.forward(&input, 0)?;
-            let logits = logits.squeeze(0)?;
-            sample_with_penalty(&logits, &all_tokens, &mut logits_processor)?
-        }
-        ModelArch::Qwen3Dense(model) => {
-            model.clear_kv_cache();
-            let input = Tensor::new(prompt_tokens, device)?.unsqueeze(0)?;
-            let logits = model.forward(&input, 0)?;
-            let logits = logits.squeeze(0)?;
-            sample_with_penalty(&logits, &all_tokens, &mut logits_processor)?
-        }
-    };
+    arch.clear_kv_cache()?;
+    let input = Tensor::new(prompt_tokens, device)?.unsqueeze(0)?;
+    let logits = arch.forward(&input, 0)?;
+    let mut next_token = sample_with_penalty(&logits, &all_tokens, &mut logits_processor)?;
 
     let emit_token = |all_tokens: &[u32], decoded_prefix: &mut String| -> Result<bool> {
         let full = tokenizer
@@ -1521,23 +1643,9 @@ fn run_inference_streaming(
         }
 
         for index in 0..max_new.saturating_sub(1) {
-            next_token = match arch {
-                ModelArch::Qwen3Quantized(model) => {
-                    let input = Tensor::new(&[next_token], device)?.unsqueeze(0)?;
-                    let logits = model.forward(&input, prompt_tokens.len() + index)?;
-                    let logits = logits.squeeze(0)?;
-                    sample_with_penalty(&logits, &all_tokens, &mut logits_processor)?
-                }
-                ModelArch::Qwen3Dense(model) => {
-                    let input = Tensor::new(&[next_token], device)?.unsqueeze(0)?;
-                    // Dense returns [B, 1, V]; strip both leading dims.
-                    let logits = model
-                        .forward(&input, prompt_tokens.len() + index)?
-                        .squeeze(0)?
-                        .squeeze(0)?;
-                    sample_with_penalty(&logits, &all_tokens, &mut logits_processor)?
-                }
-            };
+            let input = Tensor::new(&[next_token], device)?.unsqueeze(0)?;
+            let logits = arch.forward(&input, prompt_tokens.len() + index)?;
+            next_token = sample_with_penalty(&logits, &all_tokens, &mut logits_processor)?;
             if Some(next_token) == eos_id {
                 finish_reason = "stop".into();
                 break;