AI Tutor reminder timezone update, pre-slot completion check, and account-level consistency policy

DEC-0029 - AI Tutor reminder timezone update, pre-slot completion check, and account-level consistency policy

Context

After locking permission fallback, daily cap, and not-logged-in behavior, the reminder engine still needs deterministic rules for timezone change and multi-device state.

Decision

Timezone change behavior:

• If learner timezone changes, apply new reminder timezone starting from next day.
• Do not reschedule same-day reminder by new timezone.

Pre-slot completion behavior:

• Before sending reminder at fixed slot, check required completion state for that day.
• If required is already completed, skip reminder send for that day.

Multi-device consistency:

• Daily required reminder state is account-level.
• If learner completes required item on any device, stop same-day reminder across all devices/channels for that account.

Simplicity posture:

• Keep one source of truth per account-day for reminder eligibility.

Rationale

Next-day timezone application avoids mid-day schedule churn. Pre-slot completion check prevents unnecessary reminders. Account-level state avoids cross-device inconsistency and duplicate nudges.