fix(schedule): harden calendar transition handling

packages/schedule/tool-schedule/tests/cron.spec.ts

@@ -228,6 +228,14 @@ describe('Croner calendar adapter', () => {
       occurrenceAt: '2026-11-01T05:30:00.000Z',
       nextScheduledAt: '2026-11-02T06:30:00.000Z',
     })
+    expect(resolveCronOccurrence({
+      ...overlap,
+      cron: '0,30 1 * * *',
+      scheduledAt: '2026-10-31T05:30:00.000Z',
+    }, Date.parse('2026-11-01T07:00:00.000Z'))).toEqual({
+      occurrenceAt: '2026-11-01T05:30:00.000Z',
+      nextScheduledAt: '2026-11-02T06:00:00.000Z',
+    })
     expect(createCronScheduleRecord(
       ScheduleId('schedule-overlap-after-first'),
       'after first overlap instant',
@@ -237,6 +245,18 @@ describe('Croner calendar adapter', () => {
     ).scheduledAt).toBe('2026-11-02T06:30:00.000Z')
   })
 
+  it('skips a sub-minute local-mean-time era before iterating dense safe-year matches', () => {
+    const record = createCronScheduleRecord(
+      ScheduleId('schedule-sub-minute-offset'),
+      'standard-time handoff',
+      '*/5 * * * *',
+      'Europe/Amsterdam',
+      Date.parse('0100-01-01T00:00:00.000Z'),
+    )
+    expect(new Date(record.scheduledAt).getUTCFullYear()).toBeGreaterThan(109)
+    expect(Math.abs(Date.parse(record.scheduledAt) % 60_000)).toBe(0)
+  }, 1_000)
+
   it('selects the latest current match after a persisted baseline', () => {
     const record = createCronScheduleRecord(
       ScheduleId('schedule-latest'),

packages/schedule/tool-schedule/tests/invariant.spec.ts

@@ -143,6 +143,28 @@ describe('Schedule package invariant', () => {
       }, 0)],
     })
     const fiber = await ctx.plugin(scheduleInvariant)
+    const alias = ctx.sessions.create(SessionId('schedule-historical-zone-alias'), {
+      seed: [event({
+        version: 1,
+        operation: 'create',
+        schedule: {
+          id: 'schedule-historical-zone-alias',
+          kind: 'cron',
+          prompt: 'historical zone alias',
+          cron: '0 9 * * *',
+          timeZone: 'US/Eastern',
+          scheduledAt: '2026-08-06T13:00:00.000Z',
+        },
+      }, 0)],
+    })
+    expect(() => alias.append('schedule/change', {
+      version: 1,
+      operation: 'dispatch',
+      id: ScheduleId('schedule-historical-zone-alias'),
+      occurrenceAt: '2026-08-07T13:00:00.000Z',
+      acceptedAt: '2026-08-07T14:00:00.000Z',
+      nextScheduledAt: '2026-08-08T13:00:00.000Z',
+    })).not.toThrow()
     const invalidLiveRules = [
       {
         id: 'schedule-historical-fast-cron',

packages/schedule/tool-schedule/tests/runtime.spec.ts

@@ -4,6 +4,7 @@ import AgentRegistry, { Inbox } from '@deepseek-ai/dsh-agent'
 import type { Agent, AgentCancelCause, InboxTarget } from '@deepseek-ai/dsh-agent'
 import type { UserMessage } from '@deepseek-ai/dsh-llm'
 import SessionStore, { SessionId } from '@deepseek-ai/dsh-session'
+import { Cron } from 'croner'
 import {
   MIN_RECURRING_INTERVAL_SECONDS,
   ScheduleId,
@@ -168,6 +169,43 @@ afterEach(async () => {
 })
 
 describe('Schedule timer and admission runtime', () => {
+  it('contains calendar resolution failure without permanently faulting the owner', async () => {
+    const test = await harness()
+    const invalidId = ScheduleId('schedule-invalid-zone')
+    appendCron(test, invalidId, '0 0 * * *', Date.now() - 86_400_000)
+    const wakeFailure = vi.spyOn(Cron.prototype, 'previousRuns').mockImplementation(() => {
+      throw new Error('calendar unavailable')
+    })
+    const owner = ownerFor(test)
+    owner.start()
+    await settle()
+    expect(test.followed).toEqual([])
+    wakeFailure.mockRestore()
+
+    let restoreCalendarFailure: (() => void) | undefined
+    test.controls.onReserve = () => {
+      const calendarFailure = vi.spyOn(Cron.prototype, 'previousRuns').mockImplementation(() => {
+        throw new Error('calendar unavailable')
+      })
+      restoreCalendarFailure = () => { calendarFailure.mockRestore() }
+    }
+    owner.requestDrive()
+    await settle()
+    expect(test.followed).toEqual([])
+
+    restoreCalendarFailure?.()
+    test.controls.onReserve = undefined
+    test.agent.session.append('schedule/change', { version: 1, operation: 'delete', id: invalidId })
+    appendAfter(test, 'schedule-healthy-after', 1, Date.now() - 2_000)
+    owner.requestDrive()
+    await settle()
+    expect(test.followed).toHaveLength(1)
+    expect(test.agent.session.events.some(event =>
+      event.type === 'schedule/change'
+      && event.data.operation === 'dispatch'
+      && event.data.id === 'schedule-healthy-after')).toBe(true)
+  })
+
   it('segments waits beyond the Node timer limit and rechecks the wall clock', async () => {
     const test = await harness()
     const delaySeconds = Math.ceil((MAX_TIMER_DELAY_MS + 1_500) / 1_000)