FA-77046 / Calendar recurrence rules / Open access

Window query for recurring instances with duration: count limit · case 01

A window late in a COUNT-limited series returns instances beyond the last occurrence.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

COUNT is restarted from the skip-ahead index instead of from dtstart.

VERIFIED REPAIR

At the count limit decision use `count`, leaving the other decision sites of the model unchanged.

Unsuccessful approach: The partial repair `count - k0` subtracts the skipped instances again and truncates the series early.

Case contract

Instances start at dtstart + k*interval_hours for k < count and last duration_min minutes. A window [window_start, window_end) returns every instance whose half-open span [s, s+duration) overlaps it; a zero-duration instance is returned when window_start <= s < window_end. The query may skip ahead but COUNT is always counted from dtstart. Return ISO start times (minutes).

Why this case matters

Recurring calendar series are expanded into concrete instances for display, reminders and conflict checks.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import datetime as dt
import calendar
N = 1
observations = []
def solve(dtstart, interval_hours, duration_min, count, window_start, window_end):
    first = dt.datetime.fromisoformat(dtstart)
    ws = dt.datetime.fromisoformat(window_start)
    we = dt.datetime.fromisoformat(window_end)
    dur = dt.timedelta(minutes=duration_min)
    step = dt.timedelta(hours=interval_hours)
    k0 = max(0, (ws - dur - first) // step)
    out = []
    for k in range(k0, k0 + count):
        s = first + k * step
        if s >= we:
            break
        if (s + dur > ws) if duration_min else s >= ws:
            out.append(s.isoformat(timespec='minutes'))
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: in-progress long meeting',
   ['2024-01-01T00:00', 1, 180, 20, '2024-01-01T10:30', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']),
  ('touching end excluded',
   ['2024-01-01T08:00', 2, 60, 10, '2024-01-01T09:00', '2024-01-01T12:00'],
   ['2024-01-01T10:00']),
  ('window end exclusive',
   ['2024-01-01T08:00', 2, 30, 10, '2024-01-01T08:15', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T10:00']),
  ('zero duration instants',
   ['2024-01-01T00:00', 6, 0, 10, '2024-01-01T12:00', '2024-01-02T00:00'],
   ['2024-01-01T12:00', '2024-01-01T18:00']),
  ('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00']),
  ('window before dtstart',
   ['2024-01-05T09:00', 24, 90, 3, '2024-01-01T00:00', '2024-01-06T12:00'],
   ['2024-01-05T09:00', '2024-01-06T09:00']),
  ('duration longer than interval',
   ['2024-02-01T00:00', 2, 300, 12, '2024-02-01T09:00', '2024-02-01T10:00'],
   ['2024-02-01T06:00', '2024-02-01T08:00'])],
 [('window end exclusive',
   ['2024-01-01T08:00', 2, 30, 10, '2024-01-01T08:15', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T10:00']),
  ('zero duration instants',
   ['2024-01-01T00:00', 6, 0, 10, '2024-01-01T12:00', '2024-01-02T00:00'],
   ['2024-01-01T12:00', '2024-01-01T18:00']),
  ('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00']),
  ('window before dtstart',
   ['2024-01-05T09:00', 24, 90, 3, '2024-01-01T00:00', '2024-01-06T12:00'],
   ['2024-01-05T09:00', '2024-01-06T09:00']),
  ('duration longer than interval',
   ['2024-02-01T00:00', 2, 300, 12, '2024-02-01T09:00', '2024-02-01T10:00'],
   ['2024-02-01T06:00', '2024-02-01T08:00']),
  ('window mid series',
   ['2024-03-01T06:00', 4, 120, 30, '2024-03-02T07:00', '2024-03-02T15:00'],
   ['2024-03-02T06:00', '2024-03-02T10:00', '2024-03-02T14:00']),
  ('instance ends at window start',
   ['2024-03-01T00:00', 3, 180, 8, '2024-03-01T06:00', '2024-03-01T07:00'],
   ['2024-03-01T06:00'])],
 [('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00']),
  ('window before dtstart',
   ['2024-01-05T09:00', 24, 90, 3, '2024-01-01T00:00', '2024-01-06T12:00'],
   ['2024-01-05T09:00', '2024-01-06T09:00']),
  ('duration longer than interval',
   ['2024-02-01T00:00', 2, 300, 12, '2024-02-01T09:00', '2024-02-01T10:00'],
   ['2024-02-01T06:00', '2024-02-01T08:00']),
  ('window mid series',
   ['2024-03-01T06:00', 4, 120, 30, '2024-03-02T07:00', '2024-03-02T15:00'],
   ['2024-03-02T06:00', '2024-03-02T10:00', '2024-03-02T14:00']),
  ('instance ends at window start',
   ['2024-03-01T00:00', 3, 180, 8, '2024-03-01T06:00', '2024-03-01T07:00'],
   ['2024-03-01T06:00']),
  ('count exactly reaches window',
   ['2024-04-01T00:00', 12, 60, 4, '2024-04-02T11:30', '2024-04-03T00:00'],
   ['2024-04-02T12:00']),
  ('long instance from before window, short count',
   ['2024-05-01T00:00', 1, 600, 3, '2024-05-01T05:00', '2024-05-01T06:00'],
   ['2024-05-01T00:00', '2024-05-01T01:00', '2024-05-01T02:00'])],
 [('duration longer than interval',
   ['2024-02-01T00:00', 2, 300, 12, '2024-02-01T09:00', '2024-02-01T10:00'],
   ['2024-02-01T06:00', '2024-02-01T08:00']),
  ('window mid series',
   ['2024-03-01T06:00', 4, 120, 30, '2024-03-02T07:00', '2024-03-02T15:00'],
   ['2024-03-02T06:00', '2024-03-02T10:00', '2024-03-02T14:00']),
  ('instance ends at window start',
   ['2024-03-01T00:00', 3, 180, 8, '2024-03-01T06:00', '2024-03-01T07:00'],
   ['2024-03-01T06:00']),
  ('count exactly reaches window',
   ['2024-04-01T00:00', 12, 60, 4, '2024-04-02T11:30', '2024-04-03T00:00'],
   ['2024-04-02T12:00']),
  ('long instance from before window, short count',
   ['2024-05-01T00:00', 1, 600, 3, '2024-05-01T05:00', '2024-05-01T06:00'],
   ['2024-05-01T00:00', '2024-05-01T01:00', '2024-05-01T02:00']),
  ('regression: in-progress long meeting',
   ['2024-01-01T00:00', 1, 180, 20, '2024-01-01T10:30', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']),
  ('touching end excluded',
   ['2024-01-01T08:00', 2, 60, 10, '2024-01-01T09:00', '2024-01-01T12:00'],
   ['2024-01-01T10:00']),
  ('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00'])],
 [('instance ends at window start',
   ['2024-03-01T00:00', 3, 180, 8, '2024-03-01T06:00', '2024-03-01T07:00'],
   ['2024-03-01T06:00']),
  ('count exactly reaches window',
   ['2024-04-01T00:00', 12, 60, 4, '2024-04-02T11:30', '2024-04-03T00:00'],
   ['2024-04-02T12:00']),
  ('long instance from before window, short count',
   ['2024-05-01T00:00', 1, 600, 3, '2024-05-01T05:00', '2024-05-01T06:00'],
   ['2024-05-01T00:00', '2024-05-01T01:00', '2024-05-01T02:00']),
  ('regression: in-progress long meeting',
   ['2024-01-01T00:00', 1, 180, 20, '2024-01-01T10:30', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']),
  ('touching end excluded',
   ['2024-01-01T08:00', 2, 60, 10, '2024-01-01T09:00', '2024-01-01T12:00'],
   ['2024-01-01T10:00']),
  ('window end exclusive',
   ['2024-01-01T08:00', 2, 30, 10, '2024-01-01T08:15', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T10:00']),
  ('zero duration instants',
   ['2024-01-01T00:00', 6, 0, 10, '2024-01-01T12:00', '2024-01-02T00:00'],
   ['2024-01-01T12:00', '2024-01-01T18:00']),
  ('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00'])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
regression: in-progress long meeting	`['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']`	`['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']`	Passed
touching end excluded	`['2024-01-01T10:00']`	`['2024-01-01T10:00']`	Passed
window end exclusive	`['2024-01-01T08:00', '2024-01-01T10:00']`	`['2024-01-01T08:00', '2024-01-01T10:00']`	Passed
zero duration instants	`['2024-01-01T12:00', '2024-01-01T18:00']`	`['2024-01-01T12:00', '2024-01-01T18:00']`	Passed
late window beyond count	`['2024-01-04T00:00', '2024-01-05T00:00', '2024-01-06T00:00', '2024-01-07T00:00']`	`['2024-01-04T00:00', '2024-01-05T00:00']`	Failed
window before dtstart	`['2024-01-05T09:00', '2024-01-06T09:00']`	`['2024-01-05T09:00', '2024-01-06T09:00']`	Passed
duration longer than interval	`['2024-02-01T06:00', '2024-02-01T08:00']`	`['2024-02-01T06:00', '2024-02-01T08:00']`	Passed

SHA-256 / 734d25dc5285fcfd3bce0fb89353e0227102a35cfea28e209c3537bbfb16cb3b

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import datetime as dt
import calendar
N = 1
observations = []
def solve(dtstart, interval_hours, duration_min, count, window_start, window_end):
    first = dt.datetime.fromisoformat(dtstart)
    ws = dt.datetime.fromisoformat(window_start)
    we = dt.datetime.fromisoformat(window_end)
    dur = dt.timedelta(minutes=duration_min)
    step = dt.timedelta(hours=interval_hours)
    k0 = max(0, (ws - dur - first) // step)
    out = []
    for k in range(k0, count - k0):
        s = first + k * step
        if s >= we:
            break
        if (s + dur > ws) if duration_min else s >= ws:
            out.append(s.isoformat(timespec='minutes'))
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: in-progress long meeting',
   ['2024-01-01T00:00', 1, 180, 20, '2024-01-01T10:30', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']),
  ('touching end excluded',
   ['2024-01-01T08:00', 2, 60, 10, '2024-01-01T09:00', '2024-01-01T12:00'],
   ['2024-01-01T10:00']),
  ('window end exclusive',
   ['2024-01-01T08:00', 2, 30, 10, '2024-01-01T08:15', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T10:00']),
  ('zero duration instants',
   ['2024-01-01T00:00', 6, 0, 10, '2024-01-01T12:00', '2024-01-02T00:00'],
   ['2024-01-01T12:00', '2024-01-01T18:00']),
  ('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00']),
  ('window before dtstart',
   ['2024-01-05T09:00', 24, 90, 3, '2024-01-01T00:00', '2024-01-06T12:00'],
   ['2024-01-05T09:00', '2024-01-06T09:00']),
  ('duration longer than interval',
   ['2024-02-01T00:00', 2, 300, 12, '2024-02-01T09:00', '2024-02-01T10:00'],
   ['2024-02-01T06:00', '2024-02-01T08:00'])],
 [('window end exclusive',
   ['2024-01-01T08:00', 2, 30, 10, '2024-01-01T08:15', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T10:00']),
  ('zero duration instants',
   ['2024-01-01T00:00', 6, 0, 10, '2024-01-01T12:00', '2024-01-02T00:00'],
   ['2024-01-01T12:00', '2024-01-01T18:00']),
  ('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00']),
  ('window before dtstart',
   ['2024-01-05T09:00', 24, 90, 3, '2024-01-01T00:00', '2024-01-06T12:00'],
   ['2024-01-05T09:00', '2024-01-06T09:00']),
  ('duration longer than interval',
   ['2024-02-01T00:00', 2, 300, 12, '2024-02-01T09:00', '2024-02-01T10:00'],
   ['2024-02-01T06:00', '2024-02-01T08:00']),
  ('window mid series',
   ['2024-03-01T06:00', 4, 120, 30, '2024-03-02T07:00', '2024-03-02T15:00'],
   ['2024-03-02T06:00', '2024-03-02T10:00', '2024-03-02T14:00']),
  ('instance ends at window start',
   ['2024-03-01T00:00', 3, 180, 8, '2024-03-01T06:00', '2024-03-01T07:00'],
   ['2024-03-01T06:00'])],
 [('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00']),
  ('window before dtstart',
   ['2024-01-05T09:00', 24, 90, 3, '2024-01-01T00:00', '2024-01-06T12:00'],
   ['2024-01-05T09:00', '2024-01-06T09:00']),
  ('duration longer than interval',
   ['2024-02-01T00:00', 2, 300, 12, '2024-02-01T09:00', '2024-02-01T10:00'],
   ['2024-02-01T06:00', '2024-02-01T08:00']),
  ('window mid series',
   ['2024-03-01T06:00', 4, 120, 30, '2024-03-02T07:00', '2024-03-02T15:00'],
   ['2024-03-02T06:00', '2024-03-02T10:00', '2024-03-02T14:00']),
  ('instance ends at window start',
   ['2024-03-01T00:00', 3, 180, 8, '2024-03-01T06:00', '2024-03-01T07:00'],
   ['2024-03-01T06:00']),
  ('count exactly reaches window',
   ['2024-04-01T00:00', 12, 60, 4, '2024-04-02T11:30', '2024-04-03T00:00'],
   ['2024-04-02T12:00']),
  ('long instance from before window, short count',
   ['2024-05-01T00:00', 1, 600, 3, '2024-05-01T05:00', '2024-05-01T06:00'],
   ['2024-05-01T00:00', '2024-05-01T01:00', '2024-05-01T02:00'])],
 [('duration longer than interval',
   ['2024-02-01T00:00', 2, 300, 12, '2024-02-01T09:00', '2024-02-01T10:00'],
   ['2024-02-01T06:00', '2024-02-01T08:00']),
  ('window mid series',
   ['2024-03-01T06:00', 4, 120, 30, '2024-03-02T07:00', '2024-03-02T15:00'],
   ['2024-03-02T06:00', '2024-03-02T10:00', '2024-03-02T14:00']),
  ('instance ends at window start',
   ['2024-03-01T00:00', 3, 180, 8, '2024-03-01T06:00', '2024-03-01T07:00'],
   ['2024-03-01T06:00']),
  ('count exactly reaches window',
   ['2024-04-01T00:00', 12, 60, 4, '2024-04-02T11:30', '2024-04-03T00:00'],
   ['2024-04-02T12:00']),
  ('long instance from before window, short count',
   ['2024-05-01T00:00', 1, 600, 3, '2024-05-01T05:00', '2024-05-01T06:00'],
   ['2024-05-01T00:00', '2024-05-01T01:00', '2024-05-01T02:00']),
  ('regression: in-progress long meeting',
   ['2024-01-01T00:00', 1, 180, 20, '2024-01-01T10:30', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']),
  ('touching end excluded',
   ['2024-01-01T08:00', 2, 60, 10, '2024-01-01T09:00', '2024-01-01T12:00'],
   ['2024-01-01T10:00']),
  ('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00'])],
 [('instance ends at window start',
   ['2024-03-01T00:00', 3, 180, 8, '2024-03-01T06:00', '2024-03-01T07:00'],
   ['2024-03-01T06:00']),
  ('count exactly reaches window',
   ['2024-04-01T00:00', 12, 60, 4, '2024-04-02T11:30', '2024-04-03T00:00'],
   ['2024-04-02T12:00']),
  ('long instance from before window, short count',
   ['2024-05-01T00:00', 1, 600, 3, '2024-05-01T05:00', '2024-05-01T06:00'],
   ['2024-05-01T00:00', '2024-05-01T01:00', '2024-05-01T02:00']),
  ('regression: in-progress long meeting',
   ['2024-01-01T00:00', 1, 180, 20, '2024-01-01T10:30', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']),
  ('touching end excluded',
   ['2024-01-01T08:00', 2, 60, 10, '2024-01-01T09:00', '2024-01-01T12:00'],
   ['2024-01-01T10:00']),
  ('window end exclusive',
   ['2024-01-01T08:00', 2, 30, 10, '2024-01-01T08:15', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T10:00']),
  ('zero duration instants',
   ['2024-01-01T00:00', 6, 0, 10, '2024-01-01T12:00', '2024-01-02T00:00'],
   ['2024-01-01T12:00', '2024-01-01T18:00']),
  ('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00'])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
regression: in-progress long meeting	`['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']`	`['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']`	Passed
touching end excluded	`['2024-01-01T10:00']`	`['2024-01-01T10:00']`	Passed
window end exclusive	`['2024-01-01T08:00', '2024-01-01T10:00']`	`['2024-01-01T08:00', '2024-01-01T10:00']`	Passed
zero duration instants	`['2024-01-01T12:00', '2024-01-01T18:00']`	`['2024-01-01T12:00', '2024-01-01T18:00']`	Passed
late window beyond count	`[]`	`['2024-01-04T00:00', '2024-01-05T00:00']`	Failed
window before dtstart	`['2024-01-05T09:00', '2024-01-06T09:00']`	`['2024-01-05T09:00', '2024-01-06T09:00']`	Passed
duration longer than interval	`['2024-02-01T06:00', '2024-02-01T08:00']`	`['2024-02-01T06:00', '2024-02-01T08:00']`	Passed

SHA-256 / 650ced9036f19ddd6b67a24f6ebcd7dd56c2dace73b0340422c742d57114b77e

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import datetime as dt
import calendar
N = 1
observations = []
def solve(dtstart, interval_hours, duration_min, count, window_start, window_end):
    first = dt.datetime.fromisoformat(dtstart)
    ws = dt.datetime.fromisoformat(window_start)
    we = dt.datetime.fromisoformat(window_end)
    dur = dt.timedelta(minutes=duration_min)
    step = dt.timedelta(hours=interval_hours)
    k0 = max(0, (ws - dur - first) // step)
    out = []
    for k in range(k0, count):
        s = first + k * step
        if s >= we:
            break
        if (s + dur > ws) if duration_min else s >= ws:
            out.append(s.isoformat(timespec='minutes'))
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: in-progress long meeting',
   ['2024-01-01T00:00', 1, 180, 20, '2024-01-01T10:30', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']),
  ('touching end excluded',
   ['2024-01-01T08:00', 2, 60, 10, '2024-01-01T09:00', '2024-01-01T12:00'],
   ['2024-01-01T10:00']),
  ('window end exclusive',
   ['2024-01-01T08:00', 2, 30, 10, '2024-01-01T08:15', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T10:00']),
  ('zero duration instants',
   ['2024-01-01T00:00', 6, 0, 10, '2024-01-01T12:00', '2024-01-02T00:00'],
   ['2024-01-01T12:00', '2024-01-01T18:00']),
  ('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00']),
  ('window before dtstart',
   ['2024-01-05T09:00', 24, 90, 3, '2024-01-01T00:00', '2024-01-06T12:00'],
   ['2024-01-05T09:00', '2024-01-06T09:00']),
  ('duration longer than interval',
   ['2024-02-01T00:00', 2, 300, 12, '2024-02-01T09:00', '2024-02-01T10:00'],
   ['2024-02-01T06:00', '2024-02-01T08:00'])],
 [('window end exclusive',
   ['2024-01-01T08:00', 2, 30, 10, '2024-01-01T08:15', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T10:00']),
  ('zero duration instants',
   ['2024-01-01T00:00', 6, 0, 10, '2024-01-01T12:00', '2024-01-02T00:00'],
   ['2024-01-01T12:00', '2024-01-01T18:00']),
  ('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00']),
  ('window before dtstart',
   ['2024-01-05T09:00', 24, 90, 3, '2024-01-01T00:00', '2024-01-06T12:00'],
   ['2024-01-05T09:00', '2024-01-06T09:00']),
  ('duration longer than interval',
   ['2024-02-01T00:00', 2, 300, 12, '2024-02-01T09:00', '2024-02-01T10:00'],
   ['2024-02-01T06:00', '2024-02-01T08:00']),
  ('window mid series',
   ['2024-03-01T06:00', 4, 120, 30, '2024-03-02T07:00', '2024-03-02T15:00'],
   ['2024-03-02T06:00', '2024-03-02T10:00', '2024-03-02T14:00']),
  ('instance ends at window start',
   ['2024-03-01T00:00', 3, 180, 8, '2024-03-01T06:00', '2024-03-01T07:00'],
   ['2024-03-01T06:00'])],
 [('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00']),
  ('window before dtstart',
   ['2024-01-05T09:00', 24, 90, 3, '2024-01-01T00:00', '2024-01-06T12:00'],
   ['2024-01-05T09:00', '2024-01-06T09:00']),
  ('duration longer than interval',
   ['2024-02-01T00:00', 2, 300, 12, '2024-02-01T09:00', '2024-02-01T10:00'],
   ['2024-02-01T06:00', '2024-02-01T08:00']),
  ('window mid series',
   ['2024-03-01T06:00', 4, 120, 30, '2024-03-02T07:00', '2024-03-02T15:00'],
   ['2024-03-02T06:00', '2024-03-02T10:00', '2024-03-02T14:00']),
  ('instance ends at window start',
   ['2024-03-01T00:00', 3, 180, 8, '2024-03-01T06:00', '2024-03-01T07:00'],
   ['2024-03-01T06:00']),
  ('count exactly reaches window',
   ['2024-04-01T00:00', 12, 60, 4, '2024-04-02T11:30', '2024-04-03T00:00'],
   ['2024-04-02T12:00']),
  ('long instance from before window, short count',
   ['2024-05-01T00:00', 1, 600, 3, '2024-05-01T05:00', '2024-05-01T06:00'],
   ['2024-05-01T00:00', '2024-05-01T01:00', '2024-05-01T02:00'])],
 [('duration longer than interval',
   ['2024-02-01T00:00', 2, 300, 12, '2024-02-01T09:00', '2024-02-01T10:00'],
   ['2024-02-01T06:00', '2024-02-01T08:00']),
  ('window mid series',
   ['2024-03-01T06:00', 4, 120, 30, '2024-03-02T07:00', '2024-03-02T15:00'],
   ['2024-03-02T06:00', '2024-03-02T10:00', '2024-03-02T14:00']),
  ('instance ends at window start',
   ['2024-03-01T00:00', 3, 180, 8, '2024-03-01T06:00', '2024-03-01T07:00'],
   ['2024-03-01T06:00']),
  ('count exactly reaches window',
   ['2024-04-01T00:00', 12, 60, 4, '2024-04-02T11:30', '2024-04-03T00:00'],
   ['2024-04-02T12:00']),
  ('long instance from before window, short count',
   ['2024-05-01T00:00', 1, 600, 3, '2024-05-01T05:00', '2024-05-01T06:00'],
   ['2024-05-01T00:00', '2024-05-01T01:00', '2024-05-01T02:00']),
  ('regression: in-progress long meeting',
   ['2024-01-01T00:00', 1, 180, 20, '2024-01-01T10:30', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']),
  ('touching end excluded',
   ['2024-01-01T08:00', 2, 60, 10, '2024-01-01T09:00', '2024-01-01T12:00'],
   ['2024-01-01T10:00']),
  ('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00'])],
 [('instance ends at window start',
   ['2024-03-01T00:00', 3, 180, 8, '2024-03-01T06:00', '2024-03-01T07:00'],
   ['2024-03-01T06:00']),
  ('count exactly reaches window',
   ['2024-04-01T00:00', 12, 60, 4, '2024-04-02T11:30', '2024-04-03T00:00'],
   ['2024-04-02T12:00']),
  ('long instance from before window, short count',
   ['2024-05-01T00:00', 1, 600, 3, '2024-05-01T05:00', '2024-05-01T06:00'],
   ['2024-05-01T00:00', '2024-05-01T01:00', '2024-05-01T02:00']),
  ('regression: in-progress long meeting',
   ['2024-01-01T00:00', 1, 180, 20, '2024-01-01T10:30', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']),
  ('touching end excluded',
   ['2024-01-01T08:00', 2, 60, 10, '2024-01-01T09:00', '2024-01-01T12:00'],
   ['2024-01-01T10:00']),
  ('window end exclusive',
   ['2024-01-01T08:00', 2, 30, 10, '2024-01-01T08:15', '2024-01-01T12:00'],
   ['2024-01-01T08:00', '2024-01-01T10:00']),
  ('zero duration instants',
   ['2024-01-01T00:00', 6, 0, 10, '2024-01-01T12:00', '2024-01-02T00:00'],
   ['2024-01-01T12:00', '2024-01-01T18:00']),
  ('late window beyond count',
   ['2024-01-01T00:00', 24, 60, 5, '2024-01-04T00:00', '2024-01-10T00:00'],
   ['2024-01-04T00:00', '2024-01-05T00:00'])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
regression: in-progress long meeting	`['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']`	`['2024-01-01T08:00', '2024-01-01T09:00', '2024-01-01T10:00', '2024-01-01T11:00']`	Passed
touching end excluded	`['2024-01-01T10:00']`	`['2024-01-01T10:00']`	Passed
window end exclusive	`['2024-01-01T08:00', '2024-01-01T10:00']`	`['2024-01-01T08:00', '2024-01-01T10:00']`	Passed
zero duration instants	`['2024-01-01T12:00', '2024-01-01T18:00']`	`['2024-01-01T12:00', '2024-01-01T18:00']`	Passed
late window beyond count	`['2024-01-04T00:00', '2024-01-05T00:00']`	`['2024-01-04T00:00', '2024-01-05T00:00']`	Passed
window before dtstart	`['2024-01-05T09:00', '2024-01-06T09:00']`	`['2024-01-05T09:00', '2024-01-06T09:00']`	Passed
duration longer than interval	`['2024-02-01T06:00', '2024-02-01T08:00']`	`['2024-02-01T06:00', '2024-02-01T08:00']`	Passed

SHA-256 / e1916d8062d45d00e3226e140d2f9112e3b29b46f159510640eef9984ff45fd9

Verification & scope

Stipulated, bounded recurrence-expansion model evaluated offline on explicit fixtures; it is not a complete iCalendar implementation and makes no claim of standards conformance. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:49:21.893044+00:00.

Case digest / 1b6477aee1efacb2fee5a763007ff5d606b1e710a0eb4f5fc84cd47dccff954a