Function ifds_program_cache_key_from_program 

pub fn ifds_program_cache_key_from_program(
    program: &Program,
) -> Result<IfdsCsrProgramCacheKey, String>

Recover the exploded IFDS program cache key baked into a generated CSR builder Program.

Test and parity dispatchers use this to route GPU-shaped byte inputs through the CPU reference without re-deriving dimensions from padded buffers alone.