Local image generation backend for Blazen using diffusion-rs.

This crate wraps the diffusion-rs pure-Rust Stable Diffusion inference engine to provide fully local, offline image generation with no API keys required.

When used through blazen-llm with the diffusion feature flag, this crate's [DiffusionProvider] will implement blazen_llm::ImageGeneration.

Feature flags

Without the engine feature the crate compiles (options struct + stub provider) but cannot actually run image generation. This keeps workspace builds fast when the heavy native dependencies are not needed.

Streaming support

Image generation through this crate is single-call: one [DiffusionProvider::generate_image] invocation returns one complete [blazen_llm::ImageResult]. There is no per-step callback or partial result stream.

Upstream diffusion-rs does expose a gen_img_with_progress(&Config, &mut ModelConfig, Sender<Progress>) entry point that emits (step, total_steps, time) triples over a [std::sync::mpsc::Sender], but the Progress fields are private (only Debug is implemented) so they can be logged but not meaningfully surfaced through Blazen's typed APIs. Wiring richer progress events would require either upstream exposing public accessors or building a progress facade in this crate that re-formats the Debug output -- both are out of scope for the initial engine wire-up.