fix(backend): background-job UTC date skew + retire redundant Discord notifier

[thomasluizon]

What & why

Production was throwing a recurring 500 (surfaced via the new Sentry pipeline): the reminder background job's batched INSERT into Notifications + SentReminders kept hitting the SentReminders unique dedup index.

Root cause: ReminderSchedulerService.ProcessRelativeReminders deduped its bulk pre-check against Date == utcToday, but HabitLog.Date and SentReminder.Date store the user's local date (set via UserDateService.GetUserTodayAsync). For any user whose local calendar date differs from UTC's (e.g. Brazil, UTC-3, after UTC midnight), the pre-check looked in the wrong day bucket, missed the already-sent row, and re-attempted the insert on every 1-minute tick → unique-violation → EF logs it at Error → Sentry alert. The collision is caught gracefully (no duplicate push), so no user-facing harm — but a steady stream of error noise. The sibling ProcessScheduledReminders already handled this with a ±1-day window.

Changes

• ReminderSchedulerService.ProcessRelativeReminders — query the utcToday-1 .. utcToday+1 window and key both the dedup set and the logged-habit set on the user's local date (mirrors ProcessScheduledReminders). Fixes the SentReminder.Date skew (the error) and the parallel HabitLog.Date skew (was sending reminders for already-logged habits to off-UTC users).
• GoalDeadlineNotificationService / StreakGoalSyncService — found by a full audit of the same bug class. Both load streak logs with a UTC-derived lower bound against the user-local HabitLog.Date. Widened the bound by one day so a far-west user's oldest in-window logs aren't clipped. Pure widening — can't overcount (the streak walk still uses userToday).

Inspected and intentionally NOT changed

• HabitDueDateAdvancementService — its bulk filter uses a UTC ConservativeCutoffUtc(), but there is a separate authoritative per-user check ShouldAdvanceForUserToday (DueDate < userToday). The UTC pre-filter only ever delays a deliberately-conservative process by ≤1 day; it never advances wrongly. Making it more aggressive risks the "re-hides overdue" regression. Left as-is by design.

Also: observability cleanup (retire code-level Discord notifier)

With orbit-api added to the Sentry→Discord alert rule, the bespoke DiscordAlertNotifier is redundant — UnhandledExceptionHandler already SentrySdk.CaptureExceptions every 500, and the notifier double-pinged Discord on 500s. Removed so all three projects alert through one mechanism (Sentry → Discord), with messages linking to full issue context.

Deletes DiscordAlertNotifier, IAlertNotifier, DiscordAlertSettings, the "Discord" HttpClient + DiscordAlerts config section, and the now-unused notifier arg in UnhandledExceptionHandler. The DiscordAlerts__WebhookUrl env var on Render is now unused (safe to delete). ⚠️ After this deploys, the API reaches Discord only via Sentry — so orbit-api must be in the Sentry→Discord rule for API errors to land in #alerts.

Tests

3 new tests in ReminderSchedulerServiceTests reproduce the cross-timezone scenario deterministically (timezone chosen from the current UTC hour so userToday ≠ utcToday every run; a guard assertion confirms it). They fail on the old code, pass on the new. Full solution: Domain 386 / Application 1995 / Infrastructure 1114 — all passing.

🤖 Generated with Claude Code

[claude]

Tight, well-reasoned fix. The relative-reminder path now mirrors the already-correct scheduled-reminder path: ±1-day window on the bulk query, dedup keyed on (HabitId, userToday) and (HabitId, userToday, MinutesBefore), and the SentReminder row written with the user-local date. The streak service lookback widening in GoalDeadlineNotificationService and StreakGoalSyncService is a pure safe broadening — the authoritative streak walk still uses userToday so it can't overcount. The three regression tests are deterministic: selecting UTC±12 based on current UTC hour guarantees userToday ≠ UtcToday regardless of when CI runs, and the guard assertion will catch any broken assumption loudly. Inspected-and-intentionally-not-changed rationale for HabitDueDateAdvancementService is solid.

[claude]

The second commit (Discord notifier retirement) is a clean, complete removal: IAlertNotifier + DiscordAlertNotifier + DiscordAlertSettings are deleted together with their DI registration, appsettings.json stanza, and tests, and UnhandledExceptionHandler's constructor is simplified. SentrySdk.CaptureException is still in place so exception capture is unaffected — the old fire-and-forget Discord call was actually an unobserved task anyway, so this is a net improvement in reliability. Combined with the already-approved reminder/streak timezone fix, both halves of this PR are solid.

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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