fix: reject impossible weekly automation schedules (#4205)

src/shared/automation-schedules.test.ts

@@ -81,6 +81,19 @@ describe('automation schedules', () => {
     expect(tryParseAutomationRrule('FREQ=WEEKLY;BYDAY=MO,NO;BYHOUR=10;BYMINUTE=15')).toBeNull()
   })
 
+  it('rejects weekly RRULE schedules that cannot match any day', () => {
+    const rrule = 'FREQ=WEEKLY;BYHOUR=9;BYMINUTE=0'
+
+    expect(isValidAutomationSchedule(rrule)).toBe(false)
+    expect(() =>
+      nextAutomationOccurrenceAfter(
+        rrule,
+        new Date('2026-05-01T00:00:00').getTime(),
+        new Date('2026-05-02T00:00:00').getTime()
+      )
+    ).toThrow('Invalid recurrence day.')
+  })
+
   it('formats invalid schedules with a safe fallback label', () => {
     expect(formatAutomationSchedule('FREQ=YEARLY')).toBe('Invalid schedule')
   })

src/shared/automation-schedules.ts

@@ -86,6 +86,13 @@ function parseRrule(rrule: string): ParsedRrule {
     throw new Error('Invalid recurrence minute.')
   }
   const byDay = (entries.get('BYDAY') ?? '').split(',').filter(Boolean)
+  if (
+    freq === 'WEEKLY' &&
+    (byDay.length === 0 ||
+      byDay.some((day) => !DAY_CODES.includes(day as (typeof DAY_CODES)[number])))
+  ) {
+    throw new Error('Invalid recurrence day.')
+  }
   return { kind: 'rrule', freq, byDay, byHour, byMinute }
 }