The per-session bound trusted whatever session_id a writer logged. The
PostToolUse hook and the agent log different ids for one review, and an
unsubstituted SESSION_ID placeholder either merged every review into one
bound or left each answer unbounded. Bucketing by the UTC day of ts
stops one burst from pinning a dimension without trusting any id;
several reviews on one day count as one. Decision A from GStack Minder.
Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>