Function apply_compaction 

pub fn apply_compaction(
    ctx: &mut ContextState,
    req: &CompactionRequest,
    verdict: &Value,
) -> Result<CompactionOutcome, String>

Fold the summarizer’s verdict into the context: absorb the summary, drop the folded messages, bump the version, evict unreferenced skill bodies (names stay — the caller drops the bodies from its cache), recount. Refuses when the context’s version has moved since the plan was made, or when the plan’s fold exceeds the messages actually present.