Function eval_template 

pub fn eval_template(language: Language, id: &str) -> String

Render a starter eval suite for language under the lesson slug id.

Pure (§2.1): the lesson_template twin for grading — it picks the language-appropriate hello-world submission and frames a minimal one-case suite (a correct verdict) as data with no filesystem access, so the result is asserted directly against the production eval parser. One case, not two: the scaffold’s job is a parseable starting point the instructor edits, and the starter course’s committed suite (with its correct and incorrect cases) remains the fuller example. The caller is responsible for id being a safe slug; add_lesson guards it.