feat: shared model primitives + Stable Diffusion scaffold

Extract shared code into hpc/models/:
- safetensors.rs: generic file loader (used by GPT-2, SD, BERT)
- layers.rs: SIMD ops (layer_norm, gelu, silu, group_norm, softmax,
  matmul_vec, dot_product) — all via crate::simd::F32x16
- api_types.rs: OpenAI-compatible envelope (Usage, FinishReason, etc.)

Add hpc/stable_diffusion/ scaffold (code only, no weights):
- clip.rs: CLIP text encoder (same transformer as GPT-2, shared layers)
- unet.rs: UNet denoiser with Conv2D, GroupNorm, SiLU, timestep embedding
- vae.rs: VAE decoder (latent→RGB)
- scheduler.rs: DDIM noise scheduler with precomputed alpha schedule
- weights.rs: safetensors loader for SD CLIP weights
- api.rs: /v1/images/generations with full pipeline

52 tests passing. Zero weight files — disk space conscious.

https://claude.ai/code/session_01Y69Vnw751w75iVSBRws7o7

Author: claude

src/hpc/mod.rs

@@ -170,10 +170,18 @@ pub mod gguf;
 #[allow(missing_docs)]
 pub mod jina;
 
+/// Shared model primitives — safetensors, SIMD layers, API types.
+#[allow(missing_docs)]
+pub mod models;
+
 /// GPT-2 inference engine — full forward pass + OpenAI-compatible API types.
 #[allow(missing_docs)]
 pub mod gpt2;
 
+/// Stable Diffusion inference — CLIP + UNet + VAE + DDIM scheduler.
+#[allow(missing_docs)]
+pub mod stable_diffusion;
+
 // jitson: JSON config → scan pipeline (parser, validator, template, precompile, packed)
 // Always available — no Cranelift dependency.
 #[allow(missing_docs)]

src/hpc/models/api_types.rs

@@ -0,0 +1,122 @@
+//! OpenAI-compatible API types shared across all model endpoints.
+//!
+//! Transport-agnostic — no HTTP framework dependency.
+//! Used by GPT-2 (/v1/completions), Stable Diffusion (/v1/images/generations),
+//! BERT/Jina (/v1/embeddings).
+
+/// Token usage statistics (shared by all endpoints).
+#[derive(Clone, Debug, Default)]
+pub struct Usage {
+    pub prompt_tokens: usize,
+    pub completion_tokens: usize,
+    pub total_tokens: usize,
+}
+
+/// Why generation stopped.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum FinishReason {
+    /// Hit stop token or stop sequence.
+    Stop,
+    /// Hit max_tokens limit.
+    Length,
+    /// Content filter triggered.
+    ContentFilter,
+}
+
+/// Error response envelope.
+#[derive(Clone, Debug)]
+pub struct ApiError {
+    pub message: String,
+    pub error_type: String,
+    pub code: Option<String>,
+}
+
+impl ApiError {
+    pub fn invalid_request(msg: impl Into<String>) -> Self {
+        Self {
+            message: msg.into(),
+            error_type: "invalid_request_error".into(),
+            code: None,
+        }
+    }
+
+    pub fn model_not_found(model: &str) -> Self {
+        Self {
+            message: format!("model '{}' not found", model),
+            error_type: "invalid_request_error".into(),
+            code: Some("model_not_found".into()),
+        }
+    }
+}
+
+/// Model info for /v1/models listing.
+#[derive(Clone, Debug)]
+pub struct ModelCard {
+    pub id: String,
+    pub owned_by: String,
+    pub created: u64,
+}
+
+/// Embedding data for /v1/embeddings response.
+#[derive(Clone, Debug)]
+pub struct EmbeddingData {
+    pub index: usize,
+    pub embedding: Vec<f32>,
+}
+
+/// /v1/embeddings response (shared by BERT, Jina, GPT-2 wte).
+#[derive(Clone, Debug)]
+pub struct EmbeddingResponse {
+    pub model: String,
+    pub data: Vec<EmbeddingData>,
+    pub usage: Usage,
+}
+
+/// Image data for /v1/images/generations response.
+#[derive(Clone, Debug)]
+pub struct ImageData {
+    /// Base64-encoded PNG, or URL if hosted.
+    pub b64_json: Option<String>,
+    pub url: Option<String>,
+    pub revised_prompt: Option<String>,
+}
+
+/// /v1/images/generations response (Stable Diffusion).
+#[derive(Clone, Debug)]
+pub struct ImageResponse {
+    pub created: u64,
+    pub data: Vec<ImageData>,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_usage_default() {
+        let u = Usage::default();
+        assert_eq!(u.prompt_tokens, 0);
+        assert_eq!(u.total_tokens, 0);
+    }
+
+    #[test]
+    fn test_api_error_invalid_request() {
+        let e = ApiError::invalid_request("bad input");
+        assert_eq!(e.error_type, "invalid_request_error");
+        assert!(e.code.is_none());
+    }
+
+    #[test]
+    fn test_api_error_model_not_found() {
+        let e = ApiError::model_not_found("gpt-5");
+        assert!(e.message.contains("gpt-5"));
+        assert_eq!(e.code.as_deref(), Some("model_not_found"));
+    }
+
+    #[test]
+    fn test_finish_reason_eq() {
+        assert_eq!(FinishReason::Stop, FinishReason::Stop);
+        assert_ne!(FinishReason::Stop, FinishReason::Length);
+        assert_ne!(FinishReason::Length, FinishReason::ContentFilter);
+    }
+}