Function build_prompt_preamble 

pub fn build_prompt_preamble(
    iteration: u32,
    max_iterations: Option<u32>,
    min_iterations: u32,
    completion_promise: &str,
    context_content: Option<&str>,
    validation_failure: Option<&str>,
    task: &str,
) -> String

Build the standard Ralph preamble for a given iteration.

This is the outer wrapper around the task content; it communicates the loop rules and the completion promise the harness must emit.