Contract 7.1.23

Participation tenure is the current stint (Jamie, 2026-09-24; Gym #264).

• clans_participation members' joined_observed_at and days_in_clan_observed count from the member's current stint, so a member back after months away gets a new member's grace. A rejoin within 7 days of leaving continues the stint before it, so leaving cannot reset a member's grace.
• first_joined_at is the member's first recorded join in the clan, beside it (clans_roster.first_observed_in_clan is the same instant).

Additive.