Lifetime totals (count · distance · ascent · elapsed time) + a last-4-weeks
count on the profile, viewer-scoped (public-only for visitors, full for the
owner).
Design records the cost decision: compute on the fly with a single aggregate
over stored columns on the owner_id-leading indexes (cheap even for power
users) — no cache table, no schema change — with a documented escape hatch to
a user_activity_stats cache if profiling ever shows it's hot.
Validates with `openspec validate --strict`. Specs only; no code.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
