Function compile_invocation 

pub fn compile_invocation(
    stage: &PlatformStage,
    domain_sections: &[RenderedSection],
    route: &PromptRoute,
    dialect: &ModelDialect,
    tool_spec_hash: &str,
) -> Result<CompiledPromptInvocation>

Compile one call’s two programs — the platform stage and the domain’s same-stage sections (possibly none) — into the invocation the ledger records (spec: “Each model call compiles two programs”).