Function bind_default_substrate 

pub async fn bind_default_substrate(
    prefer_local: bool,
    full_access: bool,
    workdir: &Path,
    image: Option<&str>,
) -> BoundEnvironment

Decide and build the execution environment.

• prefer_local — user passed --local; skip the sandbox entirely.
• full_access — user passed --full-access/-y; grant FullAccess (no HITL). Ignored inside the sandbox only in the sense that the container already isolates — it still removes the approval prompts.