Arcade 2.0 / P4: Leaderboard meta-layer — weekly reset, daily challenge, streaks, plausibility checks #166

Parent

Spec 27: #162

What to build

The come-back-tomorrow layer across all arcade games. Each game's leaderboard gains a weekly-reset board (ISO-week periods) beside the all-time board, so newcomers can realistically top a chart. A daily challenge gives everyone the same server-derived seed for that date, with its own daily board. Playing on consecutive days grows a visible streak; beating your personal best triggers a celebration even when you're off the podium. Server-side plausibility validation keeps the boards credible: per-game score ceilings, minimum-duration-versus-score pace checks, and monotonic progress sanity — implausible submissions are rejected. (Full replay verification is explicitly out of scope.)

Leaderboard storage becomes period-aware in Postgres; streaks are per-user daily-play records; the daily seed is derived server-side from the date. All request/response shapes live in the shared contract package; endpoints follow the existing arcade-scores REST patterns including rate limits. HUD: the leaderboard panel shows all-time / weekly / daily tabs, the streak counter, and today's challenge.

Acceptance criteria

• Weekly (ISO-week) and daily-challenge boards per game alongside all-time, with migration; ranks correct across period boundaries
• Daily challenge: server-provided date-derived seed, same for every player that day, played through the normal cabinets and submitted to the daily board
• Streaks: consecutive-day play tracked server-side and shown in the HUD; personal-best celebration fires on new bests in any mode
• Plausibility validation rejects over-ceiling scores, impossible score-per-duration pace, and non-monotonic submissions, with tests for accept/reject edges following existing REST test patterns
• All new wire shapes in the shared package; rate limits applied; no change to entry-bundle budget (HUD additions stay in existing lazy surfaces where possible)
• CI fully green

Blocked by

• Arcade 2.0 / P1: Juice overhaul + Snake rework (speed, levels, art) + board-table animations & sounds #163 (final Snake pace/scoring calibrates plausibility rules)
• Arcade 2.0 / P2: Merge-drop flagship cabinet (space theme, deterministic physics) #164 (merge-drop must exist for its boards/daily challenge)