pub fn context_usage(talk: &Talk, cfg: Option<&Config>) -> ContextUsageExpand description
Context usage of talk, measured against its current model.
Only the latest agent reply counts (magi’s own notes are skipped) and a reply without usage makes the answer unknown - older replies are never consulted, since a stale count passed off as current is worse than “unknown”. The window comes from the current agent’s model, so switching model moves the denominator at once.
Switching agent (or model, which is an agent change) mints a fresh CLI
session, so the next turn re-sends the whole transcript and the count
resets or jumps. Until that turn lands, the old figure is reported with
since_switch set. Deterministic: same talk and config, same answer.