fix(scheduled-tasks): fold 5th-occurrence monthly into last-weekday; align weekday-digit parsing

Address review edge cases in the monthly recurrence anchors:

- The picker no longer offers a fifth weekday (a 5th occurrence is
  always the month's last), and recurrenceToCron clamps any nth-weekday
  that resolves to a 5th occurrence to #L — so a launch date drifting to
  day 29-31 can never emit #5 and silently skip months without one.
- cronToRecurrence accepts croner's alternate Sunday digit (7) for the
  #/#L monthly anchors, matching parseCronToHumanReadable's normalizer;
  externally-authored 7#L crons now round-trip (canonicalized to 0#L).
- #5 crons are left as custom pass-through so their month-skipping
  behavior is preserved verbatim rather than rewritten.

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/scheduled-tasks/components/task-modal/recurrence-section.tsx

@@ -58,18 +58,23 @@ function frequencyOptionFor(recurrence: Recurrence): FrequencyOption {
 /**
  * The monthly sub-options, derived from the launch date the same way a calendar
  * app offers them: repeat on the day number, on the ordinal weekday of the
- * month (e.g. the third Tuesday), or on the last weekday of the month. All three
- * are always offered so the picked mode is always representable, even when the
- * launch date is changed afterward via the footer date picker.
+ * month (e.g. the third Tuesday), or on the last weekday of the month.
+ *
+ * The ordinal anchor is offered only for the 1st–4th occurrence: a 5th
+ * occurrence is always the month's last weekday, so — like a calendar app — it
+ * is folded into the "last weekday" option rather than offering a "fifth" that
+ * would silently skip months without a 5th occurrence.
  */
 function monthlyModeOptions(launch: Date): Array<{ value: MonthlyMode; label: string }> {
   const weekdayName = format(launch, 'EEEE')
-  const ordinal = ORDINALS[Math.ceil(launch.getDate() / 7) - 1]
-  return [
+  const ordinal = Math.ceil(launch.getDate() / 7)
+  const options: Array<{ value: MonthlyMode; label: string }> = [
     { value: 'day-of-month', label: `On day ${format(launch, 'd')}` },
-    { value: 'nth-weekday', label: `On the ${ordinal} ${weekdayName}` },
-    { value: 'last-weekday', label: `On the last ${weekdayName}` },
   ]
+  if (ordinal <= 4)
+    options.push({ value: 'nth-weekday', label: `On the ${ORDINALS[ordinal - 1]} ${weekdayName}` })
+  options.push({ value: 'last-weekday', label: `On the last ${weekdayName}` })
+  return options
 }
 
 interface RecurrenceSectionProps {
@@ -107,6 +112,14 @@ export function RecurrenceSection({ recurrence, onChange, launchDate }: Recurren
   const isRecurring = recurrence.frequency !== 'once'
   const selectedWeekdays = recurrence.weekdays.length > 0 ? recurrence.weekdays : [launch.getDay()]
 
+  const monthlyOptions = monthlyModeOptions(launch)
+  const monthlyMode = recurrence.monthlyMode ?? 'day-of-month'
+  // If the launch date drifted to a 5th occurrence, the nth anchor is no longer
+  // offered; fall back to "last weekday", which is exactly what it compiles to.
+  const monthlyValue = monthlyOptions.some((option) => option.value === monthlyMode)
+    ? monthlyMode
+    : 'last-weekday'
+
   const frequencyOptions = [
     { value: 'daily', label: 'Daily' },
     { value: 'weekly', label: 'Weekly' },
@@ -231,8 +244,8 @@ export function RecurrenceSection({ recurrence, onChange, launchDate }: Recurren
               <ChipModalField
                 type='dropdown'
                 title='On'
-                value={recurrence.monthlyMode ?? 'day-of-month'}
-                options={monthlyModeOptions(launch)}
+                value={monthlyValue}
+                options={monthlyOptions}
                 onChange={(value) => onChange({ ...recurrence, monthlyMode: value as MonthlyMode })}
               />
             )}

apps/sim/app/workspace/[workspaceId]/scheduled-tasks/utils/recurrence.test.ts

@@ -64,6 +64,17 @@ describe('recurrenceToCron', () => {
     ).toBe('30 9 * * 1#L')
   })
 
+  it('clamps a 5th-occurrence nth-weekday to last-weekday so no month is skipped', () => {
+    // 2026-06-29 is the fifth Monday of June; `#5` would skip months without one.
+    expect(
+      recurrenceToCron(
+        { frequency: 'monthly', weekdays: [], monthlyMode: 'nth-weekday', end: { type: 'never' } },
+        '2026-06-29',
+        '09:30'
+      )
+    ).toBe('30 9 * * 1#L')
+  })
+
   it('builds a yearly expression from the launch month and day', () => {
     expect(
       recurrenceToCron(
@@ -197,6 +208,40 @@ describe('cronToRecurrence', () => {
     ).toBe('yearly')
   })
 
+  it("accepts croner's alternate Sunday digit (7) for monthly weekday anchors", () => {
+    const nth = cronToRecurrence({
+      cronExpression: '30 9 * * 7#3',
+      maxRuns: null,
+      endsAt: null,
+      anchor,
+      timezone: 'UTC',
+    }).recurrence
+    expect(nth.frequency).toBe('monthly')
+    expect(nth.monthlyMode).toBe('nth-weekday')
+
+    const last = cronToRecurrence({
+      cronExpression: '30 9 * * 7#L',
+      maxRuns: null,
+      endsAt: null,
+      anchor,
+      timezone: 'UTC',
+    }).recurrence
+    expect(last.frequency).toBe('monthly')
+    expect(last.monthlyMode).toBe('last-weekday')
+  })
+
+  it('leaves a 5th-occurrence (#5) cron as custom so its month-skipping is preserved', () => {
+    const { recurrence } = cronToRecurrence({
+      cronExpression: '30 9 * * 1#5',
+      maxRuns: null,
+      endsAt: null,
+      anchor,
+      timezone: 'UTC',
+    })
+    expect(recurrence.frequency).toBe('custom')
+    expect(recurrence.cron).toBe('30 9 * * 1#5')
+  })
+
   it('falls back to custom for an expression it did not author', () => {
     const { recurrence } = cronToRecurrence({
       cronExpression: '*/5 * * * *',

apps/sim/app/workspace/[workspaceId]/scheduled-tasks/utils/recurrence.ts

@@ -73,8 +73,16 @@ export function recurrenceToCron(
     case 'monthly': {
       const weekday = launchDay.getUTCDay()
       switch (recurrence.monthlyMode ?? 'day-of-month') {
-        case 'nth-weekday':
-          return `${minute} ${hour} * * ${weekday}#${Math.ceil(launchDay.getUTCDate() / 7)}`
+        case 'nth-weekday': {
+          // A 5th occurrence is always the last weekday of the month; emit `#L`
+          // rather than `#5` so no month without a 5th occurrence is silently
+          // skipped (the picker only offers nth for the 1st–4th, but the launch
+          // date can still drift to a 5th via the footer date picker).
+          const nth = Math.ceil(launchDay.getUTCDate() / 7)
+          return nth >= 5
+            ? `${minute} ${hour} * * ${weekday}#L`
+            : `${minute} ${hour} * * ${weekday}#${nth}`
+        }
         case 'last-weekday':
           return `${minute} ${hour} * * ${weekday}#L`
         default:
@@ -181,13 +189,18 @@ export function cronToRecurrence(params: {
       const weekdays = dayOfWeek.split(',').map(Number)
       return { recurrence: { frequency: 'weekly', weekdays, end }, launchTime }
     }
-    if (dayOfMonth === '*' && /^[0-6]#[1-5]$/.test(dayOfWeek)) {
+    // Accept croner's alternate Sunday digit (`7`) so externally-authored
+    // `7#…` crons round-trip; the picker canonicalizes them to `0#…` on save.
+    // A 5th occurrence (`#5`) is intentionally NOT matched — it falls through to
+    // `custom` so its month-skipping behavior is preserved verbatim rather than
+    // silently rewritten to `#L`.
+    if (dayOfMonth === '*' && /^[0-7]#[1-4]$/.test(dayOfWeek)) {
       return {
         recurrence: { frequency: 'monthly', weekdays: [], monthlyMode: 'nth-weekday', end },
         launchTime,
       }
     }
-    if (dayOfMonth === '*' && /^[0-6]#L$/.test(dayOfWeek)) {
+    if (dayOfMonth === '*' && /^[0-7]#L$/.test(dayOfWeek)) {
       return {
         recurrence: { frequency: 'monthly', weekdays: [], monthlyMode: 'last-weekday', end },
         launchTime,