Daily missions architecture

Daily missions (EXP-010, Phase 56) add active, opt-in motivation on top of the passive XP/badge/streak rewards. They run in both storage modes and add exactly one tracking table.

Pieces

Module	Role
plugins/.../missions/templates.yaml	Static mission catalog (22 templates, 5 categories), synced to the frontend by make sync-missions.
MissionTemplate (Pydantic)	Catalog entry shape (config, NOT a table).
UserMission (model)	The one new table: per-user/per-day assignment + progress + xp_awarded guard. Alembic 0021, Dexie v20, sync surface (MUTABLE).
lib/missions/generator.ts + generator.py	Deterministic (seeded PRNG) adaptive selection: one pick per difficulty slot, eligibility by history (new/active/veteran), no back-to-back repeats.
lib/missions/checks.ts + SUPPORTED_CHECK_FUNCTIONS	Only checks computable from existing data are assignable (the other 5 catalog entries stay un-assigned until tracking exists).
lib/missions/progress.ts	Pure check_function + stats snapshot -> {current, target, completed}.
lib/missions/schedule.ts	Local-midnight today (language->timezone) + streak-joker.
storage/missions-dexie.ts	Dexie: gather a "today" stats snapshot, assign idempotently, evaluate, award XP on completion.
missions plugin service.py	Same flow against SQLAlchemy for API mode (GET /today, POST /regenerate).

Flow

1. The dashboard widget (or lesson completion) calls getStorage().missions.getDaily(userId, {todayIso}).
2. If no rows exist for that local day, the generator assigns a fresh set (seeded by userId + date, excluding yesterday's).
3. Progress is re-evaluated against existing data (LessonProgress / ElementError / streak). A newly-completed mission flips completed and, once, awards its xp_reward (idempotent via xp_awarded).
4. celebrateMissions (celebration bus) plays the mission sound + surfaces a praise phrase; an all-clear plays the bigger sound + a confetti burst.

Rules

• Deterministic per (userId, date); a user uses one storage backend, so cross-backend exact parity is not required.
• No tracking beyond UserMission; un-trackable checks are not assigned.
• Missions are supplementary - a failure never breaks the lesson flow (all reads are defensive). No penalty for missed days.