A clean completion that emits a single token with no content delta never
captured firstOutputMs, so the footer's generation rate (G) computed null while
the processing rate (P) survived via the responseEndMs fallback — the stat
visibly dropped out on those turns.
Add findDisplayableTokenStats, which walks back to the most recent turn that has
a usable generation rate so a degenerate turn no longer blanks the display, and
point the footer at it. Falls back to the newest turn with any stats so P still
shows when no turn has a generation rate. findLatestPiTokenStats (persistence)
is unchanged.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
shahondin1624