[ghazy2001]

Fixes #5066

Problem

When declarative task schedules omit an explicit timezone (e.g. schedules.task({ cron: "0 * * * *" })), task.schedule.timezone evaluates to undefined. However, TaskSchedule in the database schema defaults timezone to "UTC".

During syncDeclarativeSchedules, comparing existingSchedule.timezone ("UTC") against task.schedule.timezone (undefined) evaluated to true on both timingChanged and persistedValuesChanged:

1. It triggered an unnecessary database write on every background worker deployment (taskSchedule.update).
2. It marked preserveExistingJob: !timingChanged as false, causing the scheduler engine to cancel and re-register the existing Redis job even when the schedule expression and timing were completely unchanged.

Solution

• Defaulted task schedule timezone to "UTC" via nextTimezone = task.schedule.timezone ?? "UTC" in createBackgroundWorker.server.ts across prepareDeclarativeSchedules, validate, and apply (both update and create paths).
• Made timezone optional in declarativeTasks test helper and added automated container test in createBackgroundWorker.server.test.ts verifying that omitting an explicit timezone matches existing "UTC" schedules without bumping updatedAt or replacing the scheduled Redis job.

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[github-actions]

Hi @ghazy2001, thanks for your interest in contributing!

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[devin-ai-integration]

Devin Review found 1 potential issue.

[devin-ai-integration]

🔍 Test bypasses worker metadata validation

The new test passes an omitted timezone directly to syncDeclarativeSchedules. ScheduleMetadata requires one, while schedules.task emits UTC by default. Investigate which production client can reach this case.

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