Function get_embedder 

pub fn get_embedder(
    models_dir: &Path,
) -> Result<&'static Mutex<TextEmbedding>, AppError>

Returns the process-wide singleton embedder, initializing it on first call. Subsequent calls return the cached instance regardless of models_dir.

Errors

• AppError::Embedding — ONNX model load failure or runtime initialisation error.
• AppError::Io — cache directory is inaccessible or cannot be created.