pub const PROMPT_VERSION: &'static str;Expand description
The fixed, in-repo, VERSIONED summarization prompt template (SPEC.md
TR-7: “summarization prompt is fixed and versioned in-repo”). Bump this
any time render_prompt’s wording changes — the version rides the
audit trail (super::SpanSummary::prompt_version) precisely so a later
reader can tell which wording produced a given summary.