Function build_esp32 

pub async fn build_esp32(
    project: &Project,
    options: BuildOptions,
) -> Result<PathBuf>

Build the ESP32 firmware ELF for the configured chip.

Runs cargo build inside the generated harness directory so its rust-toolchain.toml (channel esp) and .cargo/config.toml (Xtensa target, build-std, ESP-IDF environment) take effect.

Errors

Returns an error if the harness is missing, the Espressif toolchain is not installed, or Cargo fails.