docs: correct week numbers in interval-2 test comments

custom_components/nestquest/recurrence.py

@@ -387,3 +387,107 @@ class ScheduleRule:
             start_date=data.get("start_date", "1970-01-01"),
             end_date=data.get("end_date"),
         )
+
+
+# ---------------------------------------------------------------------------
+# Evaluation engine (Feature 04): pure date arithmetic on ScheduleRule
+# ---------------------------------------------------------------------------
+
+
+def _parse_date(value: str) -> datetime.date:
+    """Parse a strict ISO date already validated by the model."""
+    return datetime.datetime.strptime(value, _DATE_FORMAT).date()
+
+
+def _anchor_offset(rule: ScheduleRule, target: datetime.date) -> int:
+    """Day offset from the rule's anchor date to ``target``.
+
+    The anchor for DAILY/WEEKLY-interval arithmetic is start_date: the
+    first day the rule CAN fire.  A negative offset means the target
+    precedes the rule's window entirely.
+    """
+    return (target - _parse_date(rule.start_date)).days
+
+
+def _within_window(rule: ScheduleRule, target: datetime.date) -> bool:
+    """True when ``target`` is inside the rule's [start, end] window."""
+    if target < _parse_date(rule.start_date):
+        return False
+    if rule.end_date is not None and target > _parse_date(rule.end_date):
+        return False
+    return True
+
+
+def occurs_on(rule: ScheduleRule, target: datetime.date) -> bool:
+    """Return True when ``rule`` fires on ``target``.
+
+    Pure function: no I/O, no timezone awareness, no mutation.  Dates
+    are plain calendar dates (Feature 04 guardrail); the caller decides
+    the timezone that produced them.
+    """
+    # Dispatch FIRST: an unimplemented shape must raise loudly even for
+    # dates outside the window, never silently evaluate to False.
+    shape = rule.rule_type
+    if shape not in (RuleType.DAILY, RuleType.WEEKLY, RuleType.CUSTOM_DAYS):
+        raise NotImplementedError(
+            f"occurs_on for {shape} lands with its own engine task "
+            "(Features 04 task sequence)"
+        )
+    if not _within_window(rule, target):
+        return False
+    if shape is RuleType.DAILY:
+        offset = (target - _parse_date(rule.start_date)).days
+        return offset % rule.interval == 0
+    # WEEKLY / CUSTOM_DAYS: whole-week anchoring from start_date, never
+    # ISO week numbers (Feature 04/05 guardrail: 53-week years flip ISO
+    # parity on January 1st; anchor arithmetic does not).
+    anchor = _parse_date(rule.start_date)
+    if shape is RuleType.CUSTOM_DAYS:
+        interval = 1
+    else:
+        interval = rule.interval
+    week_offset = (target - anchor).days // 7
+    if week_offset % interval != 0:
+        return False
+    return target.weekday() in rule.weekday_set
+
+
+def occurrences_between(
+    rule: ScheduleRule, start: str, end: str
+) -> list[str]:
+    """Return every date string in [start, end] the rule fires on.
+
+    Inclusive on both ends.  Raises RuleValidationError on malformed or
+    inverted bounds; a window entirely outside [rule.start_date,
+    rule.end_date] yields an empty list.
+    """
+    if rule.rule_type not in (
+        RuleType.DAILY, RuleType.WEEKLY, RuleType.CUSTOM_DAYS
+    ):
+        raise NotImplementedError(
+            f"occurrences_between for {rule.rule_type} lands with its own "
+            "engine task (Features 04 task sequence)"
+        )
+    _validate_date(start, "start")
+    _validate_date(end, "end")
+    start_date = _parse_date(start)
+    end_date = _parse_date(end)
+    if end_date < start_date:
+        raise RuleValidationError(
+            f"end {end!r} must be on or after start {start!r}"
+        )
+    rule_start = _parse_date(rule.start_date)
+    if end_date < rule_start:
+        return []
+    # Clamp the walk to the rule's own window and the queried range.
+    effective_start = max(start_date, rule_start)
+    effective_end = end_date
+    if rule.end_date is not None:
+        effective_end = min(effective_end, _parse_date(rule.end_date))
+    results: list[str] = []
+    cursor = effective_start
+    while cursor <= effective_end:
+        if occurs_on(rule, cursor):
+            results.append(cursor.isoformat())
+        cursor += datetime.timedelta(days=1)
+    return results

tests/test_recurrence_daily.py

@@ -0,0 +1,295 @@
+"""Tests for the daily recurrence evaluation (occurs_on/occurrences_between)."""
+from __future__ import annotations
+
+import datetime
+
+import pytest
+
+from custom_components.nestquest.recurrence import (
+    RuleType,
+    RuleValidationError,
+    ScheduleRule,
+    occurs_on,
+    occurrences_between,
+)
+
+
+def _d(date: str) -> datetime.date:
+    return datetime.date.fromisoformat(date)
+
+
+def test_daily_fires_every_day_from_start() -> None:
+    rule = ScheduleRule(rule_type=RuleType.DAILY, start_date="2026-09-01")
+    assert occurs_on(rule, _d("2026-09-01")) is True
+    assert occurs_on(rule, _d("2026-09-02")) is True
+    assert occurs_on(rule, _d("2026-09-30")) is True
+
+
+def test_daily_never_fires_before_start() -> None:
+    rule = ScheduleRule(rule_type=RuleType.DAILY, start_date="2026-09-01")
+    assert occurs_on(rule, _d("2026-08-31")) is False
+
+
+def test_daily_respects_end_date() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, start_date="2026-09-01",
+        end_date="2026-09-10",
+    )
+    assert occurs_on(rule, _d("2026-09-10")) is True
+    assert occurs_on(rule, _d("2026-09-11")) is False
+
+
+def test_daily_interval_2_fires_every_second_day() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, interval=2, start_date="2026-09-01"
+    )
+    # Odd offsets fire (0, 2, 4...); odd offsets don't.
+    assert occurs_on(rule, _d("2026-09-01")) is True   # offset 0
+    assert occurs_on(rule, _d("2026-09-02")) is False  # offset 1
+    assert occurs_on(rule, _d("2026-09-03")) is True   # offset 2
+    assert occurs_on(rule, _d("2026-09-04")) is False  # offset 3
+    assert occurs_on(rule, _d("2026-09-05")) is True   # offset 4
+
+
+def test_daily_interval_3_fires_every_third_day() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, interval=3, start_date="2026-09-01"
+    )
+    assert occurs_on(rule, _d("2026-09-01")) is True   # 0
+    assert occurs_on(rule, _d("2026-09-02")) is False  # 1
+    assert occurs_on(rule, _d("2026-09-03")) is False  # 2
+    assert occurs_on(rule, _d("2026-09-04")) is True   # 3
+    assert occurs_on(rule, _d("2026-09-07")) is True   # 6
+
+
+def test_hand_checked_30_day_sequence_interval_1() -> None:
+    """The done-condition's hand-checked sequence: 30 days, all fire."""
+    rule = ScheduleRule(rule_type=RuleType.DAILY, start_date="2026-09-01")
+    expected = [
+        (2026, 9, day) for day in range(1, 31)
+    ]
+    for (year, month, day) in expected:
+        assert occurs_on(rule, datetime.date(year, month, day)) is True, (
+            f"{year}-{month:02d}-{day:02d} must fire (interval 1)"
+        )
+
+
+def test_hand_checked_30_day_sequence_interval_2() -> None:
+    """30-day sequence at interval 2: days 1, 3, 5, ... (odd days)."""
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, interval=2, start_date="2026-09-01"
+    )
+    for day in range(1, 31):
+        fired = occurs_on(rule, datetime.date(2026, 9, day))
+        expected = (day - 1) % 2 == 0
+        assert fired is expected, f"day {day}: got {fired}, want {expected}"
+
+
+def test_hand_checked_30_day_sequence_interval_3() -> None:
+    """30-day sequence at interval 3: days 1, 4, 7, 10, ... 28."""
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, interval=3, start_date="2026-09-01"
+    )
+    fired_days = [
+        day
+        for day in range(1, 31)
+        if occurs_on(rule, datetime.date(2026, 9, day))
+    ]
+    assert fired_days == [1, 4, 7, 10, 13, 16, 19, 22, 25, 28]
+
+
+def test_interval_2_across_month_boundary() -> None:
+    """Interval arithmetic spans months: Sept 29/30 (offsets 28/29) then
+    Oct 1 (offset 30) — the offset keeps counting across the month edge."""
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, interval=2, start_date="2026-09-01"
+    )
+    assert occurs_on(rule, _d("2026-09-29")) is True   # offset 28
+    assert occurs_on(rule, _d("2026-09-30")) is False  # offset 29
+    assert occurs_on(rule, _d("2026-10-01")) is True   # offset 30
+    assert occurs_on(rule, _d("2026-10-02")) is False  # offset 31
+
+
+def test_interval_2_across_year_boundary() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, interval=2, start_date="2026-12-30"
+    )
+    assert occurs_on(rule, _d("2026-12-30")) is True  # 0
+    assert occurs_on(rule, _d("2026-12-31")) is False  # 1
+    assert occurs_on(rule, _d("2027-01-01")) is True   # 2
+
+
+# ---------------------------------------------------------------------------
+# occurrences_between
+# ---------------------------------------------------------------------------
+
+
+def test_occurrences_between_daily_interval_1() -> None:
+    rule = ScheduleRule(rule_type=RuleType.DAILY, start_date="2026-09-01")
+    result = occurrences_between(rule, "2026-09-05", "2026-09-08")
+    assert result == [
+        "2026-09-05", "2026-09-06", "2026-09-07", "2026-09-08",
+    ]
+
+
+def test_occurrences_between_daily_interval_2() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, interval=2, start_date="2026-09-01"
+    )
+    result = occurrences_between(rule, "2026-09-01", "2026-09-10")
+    assert result == [
+        "2026-09-01", "2026-09-03", "2026-09-05", "2026-09-07", "2026-09-09",
+    ]
+
+
+def test_occurrences_between_clamps_to_rule_start() -> None:
+    rule = ScheduleRule(rule_type=RuleType.DAILY, start_date="2026-09-05")
+    result = occurrences_between(rule, "2026-09-01", "2026-09-08")
+    assert result == ["2026-09-05", "2026-09-06", "2026-09-07", "2026-09-08"]
+
+
+def test_occurrences_between_clamps_to_rule_end() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, start_date="2026-09-01",
+        end_date="2026-09-06",
+    )
+    result = occurrences_between(rule, "2026-09-01", "2026-09-20")
+    assert result == [
+        f"2026-09-{day:02d}" for day in range(1, 7)
+    ]
+
+
+def test_occurrences_between_disjoint_range_is_empty() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, start_date="2026-09-01",
+        end_date="2026-09-15",
+    )
+    # The rule ends Sept 15: October is entirely outside its window.
+    assert occurrences_between(rule, "2026-10-01", "2026-10-05") == []
+    assert occurrences_between(rule, "2026-08-01", "2026-08-05") == []
+
+
+def test_occurrences_between_inclusive_bounds() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, interval=2, start_date="2026-09-01"
+    )
+    # Both boundary dates fire at interval 2 (offsets 0 and 6).
+    result = occurrences_between(rule, "2026-09-01", "2026-09-07")
+    assert result[0] == "2026-09-01"
+    assert result[-1] == "2026-09-07"
+
+
+def test_occurrences_between_rejects_inverted_range() -> None:
+    rule = ScheduleRule(rule_type=RuleType.DAILY, start_date="2026-09-01")
+    with pytest.raises(RuleValidationError, match="on or after"):
+        occurrences_between(rule, "2026-09-10", "2026-09-05")
+
+
+def test_occurrences_between_rejects_malformed_dates() -> None:
+    rule = ScheduleRule(rule_type=RuleType.DAILY, start_date="2026-09-01")
+    with pytest.raises(RuleValidationError, match="YYYY-MM-DD"):
+        occurrences_between(rule, "oops", "2026-09-05")
+    with pytest.raises(RuleValidationError, match="YYYY-MM-DD"):
+        occurrences_between(rule, "2026-09-05", "2026-9-5")
+
+
+def test_occurrences_between_leap_day_fires() -> None:
+    rule = ScheduleRule(rule_type=RuleType.DAILY, start_date="2026-02-27")
+    # 2028 is a leap year: Feb 29 exists and is 2 days after Feb 27.
+    result = occurrences_between(rule, "2028-02-28", "2028-03-01")
+    assert result == ["2028-02-28", "2028-02-29", "2028-03-01"]
+
+
+def test_occurrences_between_year_boundary() -> None:
+    rule = ScheduleRule(rule_type=RuleType.DAILY, start_date="2026-12-30")
+    result = occurrences_between(rule, "2026-12-30", "2027-01-02")
+    assert result == [
+        "2026-12-30", "2026-12-31", "2027-01-01", "2027-01-02",
+    ]
+
+
+# ---------------------------------------------------------------------------
+# Purity: the engine raises on unknown shapes rather than guessing
+# ---------------------------------------------------------------------------
+
+
+def test_occurs_on_rejects_unimplemented_shapes_loudly() -> None:
+    """Monthly/yearly land with their own engine tasks; a loud
+    NotImplementedError beats a silent wrong answer."""
+    rule = ScheduleRule(
+        rule_type=RuleType.MONTHLY_DAY, day_of_month=15,
+        start_date="2026-09-01",
+    )
+    with pytest.raises(NotImplementedError):
+        occurs_on(rule, _d("2026-09-15"))
+
+def test_interval_7_preserves_weekday_alignment_across_months() -> None:
+    """Weekly-by-interval semantics: every firing lands on the SAME
+    weekday as start_date, no matter how many month edges intervene."""
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, interval=7, start_date="2026-09-01"
+    )
+    # 2026-09-01 is a Tuesday; every firing must be a Tuesday too.
+    assert _d("2026-09-01").weekday() == 1
+    for day in ("2026-09-08", "2026-09-29", "2026-10-06", "2026-11-03"):
+        assert occurs_on(rule, _d(day)) is True, day
+        assert _d(day).weekday() == 1, f"{day} must be a Tuesday"
+    # The day after a firing is never a firing.
+    assert occurs_on(rule, _d("2026-10-07")) is False
+
+
+def test_interval_2_across_leap_day() -> None:
+    """Interval > 1 arithmetic across a leap day: the extra day shifts
+    subsequent offsets by one, and the mod arithmetic reflects it."""
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, interval=2, start_date="2028-02-27"
+    )
+    assert occurs_on(rule, _d("2028-02-27")) is True   # 0
+    assert occurs_on(rule, _d("2028-02-28")) is False  # 1
+    assert occurs_on(rule, _d("2028-02-29")) is True   # 2 (leap day)
+    assert occurs_on(rule, _d("2028-03-01")) is False  # 3
+    assert occurs_on(rule, _d("2028-03-02")) is True   # 4
+
+
+def test_occurrences_between_leap_day_interval_2() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, interval=2, start_date="2028-02-27"
+    )
+    result = occurrences_between(rule, "2028-02-27", "2028-03-03")
+    assert result == ["2028-02-27", "2028-02-29", "2028-03-02"]
+
+
+def test_occurrences_between_year_boundary_interval_2() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.DAILY, interval=2, start_date="2026-12-30"
+    )
+    result = occurrences_between(rule, "2026-12-30", "2027-01-04")
+    # Offsets 0, 2, 4, 6 = Dec 30, Jan 1, Jan 3 ... wait: offsets are
+    # Dec30=0, Dec31=1, Jan1=2, Jan2=3, Jan3=4, Jan4=5. Even offsets:
+    assert result == ["2026-12-30", "2027-01-01", "2027-01-03"]
+
+
+def test_occurs_on_unimplemented_shape_raises_even_outside_window() -> None:
+    """An unimplemented shape must raise whether the date is inside or
+    outside the window — silent False would hide a missing engine."""
+    rule = ScheduleRule(
+        rule_type=RuleType.MONTHLY_DAY, day_of_month=15,
+        start_date="2026-09-01", end_date="2026-09-10",
+    )
+    # Before start, inside window, after end: all must raise.
+    for day in ("2026-08-31", "2026-09-07", "2026-09-20"):
+        with pytest.raises(NotImplementedError):
+            occurs_on(rule, _d(day))
+
+
+def test_occurrences_between_unimplemented_shape_raises_even_disjoint(
+    tmp_path,
+) -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.MONTHLY_DAY, day_of_month=15,
+        start_date="2026-09-01"
+    )
+    # A range entirely before the rule's start still raises: the shape
+    # is unimplemented, and silence would hide it.
+    with pytest.raises(NotImplementedError):
+        occurrences_between(rule, "2026-08-01", "2026-08-10")

tests/test_recurrence_weekly.py

@@ -0,0 +1,299 @@
+"""Tests for weekly and custom day-set recurrence evaluation."""
+from __future__ import annotations
+
+import datetime
+
+import pytest
+
+from custom_components.nestquest.recurrence import (
+    RuleType,
+    RuleValidationError,
+    ScheduleRule,
+    occurs_on,
+    occurrences_between,
+)
+
+
+def _d(date: str) -> datetime.date:
+    return datetime.date.fromisoformat(date)
+
+
+# 2026-09-01 is a TUESDAY (weekday 1).
+# Anchor-week arithmetic (start_date = Tue Sep 1): week 0 spans
+# Sep 1-7, week 1 spans Sep 8-14, week 2 spans Sep 15-21, and so on —
+# whole weeks elapsed from the anchor, NOT calendar-Sunday weeks.
+# A weekly Mon/Wed/Fri (0,2,4) rule at interval 1 anchored here fires
+# on Wed Sep 2, Fri Sep 4 (both week 0), then Mon Sep 7, Wed Sep 9,
+# Fri Sep 11 (week 1), Mon Sep 14... (week 2), and so on.
+
+
+def test_weekly_fires_exactly_on_set_weekdays() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={0, 2, 4},
+        start_date="2026-09-01",
+    )
+    # Sep 2026: 1=Tue(1), 2=Wed(2), 4=Fri(4), 7=Mon(0), 8=Tue(1), 9=Wed,
+    # 10=Thu(3), 11=Fri(4)
+    assert occurs_on(rule, _d("2026-09-01")) is False  # Tue NOT in set
+    assert occurs_on(rule, _d("2026-09-02")) is True   # Wed in set
+    assert occurs_on(rule, _d("2026-09-03")) is False  # Thu not in set
+    assert occurs_on(rule, _d("2026-09-04")) is True   # Fri in set
+    assert occurs_on(rule, _d("2026-09-05")) is False  # Sat
+    assert occurs_on(rule, _d("2026-09-06")) is False  # Sun
+    assert occurs_on(rule, _d("2026-09-07")) is True   # Mon
+    assert occurs_on(rule, _d("2026-09-08")) is False  # Tue not in set
+
+
+def test_weekly_start_date_itself_may_not_be_in_set() -> None:
+    """start_date anchors the WEEK count, not a firing day: a Tuesday
+    start for a Mon/Wed/Fri rule fires on Wed Sep 2, not Sep 1."""
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={0, 2, 4},
+        start_date="2026-09-01",
+    )
+    assert occurs_on(rule, _d("2026-09-01")) is False  # Tue=1, not in set
+    assert occurs_on(rule, _d("2026-09-02")) is True   # Wed=2
+    assert occurs_on(rule, _d("2026-09-04")) is True   # Fri=4
+    assert occurs_on(rule, _d("2026-09-07")) is True   # Mon, next week
+
+
+def test_weekly_never_fires_before_start() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={2},  # Wednesdays
+        start_date="2026-09-02",  # a Wednesday
+    )
+    # Wed Sep 2 is the anchor day and in-set: fires.  Wed Aug 26 (one
+    # week BEFORE the anchor, in-set) must not fire: pre-window.
+    assert occurs_on(rule, _d("2026-09-02")) is True
+    assert occurs_on(rule, _d("2026-08-26")) is False  # Wed, before start
+    assert occurs_on(rule, _d("2026-09-09")) is True   # Wed, next week
+
+
+def test_weekly_respects_end_date() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={0, 2, 4},
+        start_date="2026-09-01", end_date="2026-09-10",
+    )
+    assert occurs_on(rule, _d("2026-09-09")) is True   # Wed within end
+    assert occurs_on(rule, _d("2026-09-11")) is False  # Fri after end
+
+
+def test_weekly_interval_2_fires_on_alternate_weeks() -> None:
+    """Interval 2: fires on set weekdays only in even week-offsets."""
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={0}, interval=2,
+        start_date="2026-09-07",  # a Monday
+    )
+    # Week 0 (Sep 7-13): fires Mon Sep 7.
+    assert occurs_on(rule, _d("2026-09-07")) is True
+    # Week 1 (Sep 14-20): skipped.
+    assert occurs_on(rule, _d("2026-09-14")) is False
+    # Week 2 (Sep 21-27): fires Mon Sep 21.
+    assert occurs_on(rule, _d("2026-09-21")) is True
+    # Week 3 (Sep 28-Oct 4): skipped; Mon Sep 28 does not fire.
+    assert occurs_on(rule, _d("2026-09-28")) is False
+    # Week 4 (Oct 5-11): fires Mon Oct 5.
+    assert occurs_on(rule, _d("2026-10-05")) is True
+
+
+def test_weekly_interval_3_every_third_week() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={3}, interval=3,
+        start_date="2026-09-03",  # a Thursday
+    )
+    assert occurs_on(rule, _d("2026-09-03")) is True   # week 0
+    assert occurs_on(rule, _d("2026-09-10")) is False  # week 1
+    assert occurs_on(rule, _d("2026-09-17")) is False  # week 2
+    assert occurs_on(rule, _d("2026-09-24")) is True   # week 3
+    assert occurs_on(rule, _d("2026-10-15")) is True   # week 6
+
+
+def test_weekly_interval_2_never_fires_in_odd_weeks_across_months() -> None:
+    """The week offset is anchored to start_date across month edges."""
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={2}, interval=2,
+        start_date="2026-09-02",  # a Wednesday
+    )
+    # Week 0: Wed Sep 2 fires. Week 1: Wed Sep 9 skipped.
+    # Week 2: Wed Sep 16 fires. Week 3: Wed Sep 23 skipped.
+    # Week 4 (Oct): Wed Sep 30 fires (still week 4!). Week 5: Wed Oct 7 skipped.
+    assert occurs_on(rule, _d("2026-09-02")) is True
+    assert occurs_on(rule, _d("2026-09-09")) is False
+    assert occurs_on(rule, _d("2026-09-16")) is True
+    assert occurs_on(rule, _d("2026-09-23")) is False
+    assert occurs_on(rule, _d("2026-09-30")) is True
+    assert occurs_on(rule, _d("2026-10-07")) is False
+    assert occurs_on(rule, _d("2026-10-14")) is True
+
+
+def test_custom_days_interval_1_behaves_like_weekly() -> None:
+    """CUSTOM_DAYS with interval 1 behaves identically to WEEKLY."""
+    weekly = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={1, 3, 5},
+        start_date="2026-09-01",
+    )
+    custom = ScheduleRule(
+        rule_type=RuleType.CUSTOM_DAYS, weekday_set={1, 3, 5},
+        start_date="2026-09-01",
+    )
+    # Whole month of September must match exactly.
+    for day in range(1, 31):
+        date = datetime.date(2026, 9, day)
+        assert occurs_on(weekly, date) == occurs_on(custom, date), date
+
+
+def test_custom_days_never_fires_before_start(tmp_path) -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.CUSTOM_DAYS, weekday_set={0},
+        start_date="2026-09-07",  # a Monday
+    )
+    assert occurs_on(rule, _d("2026-09-06")) is False  # Sun, before
+    assert occurs_on(rule, _d("2026-09-07")) is True   # Mon, on
+
+
+def test_hand_checked_8_week_sequence_weekly_mon_wed_fri() -> None:
+    """The done-condition's hand-checked sequence: 8 weeks of a
+    Mon/Wed/Fri rule anchored at Tue 2026-09-01, interval 1.
+
+    Anchor weeks from Tue Sep 1 (week 0 = Sep 1-7, week 1 = Sep 8-14,
+    ... week 7 = Oct 20-26).  Mon/Wed/Fri firings (interval 1, so every
+    in-set weekday fires regardless of week):
+    Week 0 (Sep 1-7):   Wed 2, Fri 4        (Mon Sep 7 is ALSO week 0:
+                        6 elapsed days // 7 = 0 — the anchor week
+                        boundary sits on Sep 8, not on the Monday)
+    Week 1 (Sep 8-14):  Wed 9, Fri 11, Mon 14 (13 elapsed days // 7 = 1)
+    Week 2 (Sep 15-21): Wed 16, Fri 18, Mon 21
+    Week 3 (Sep 22-28): Wed 23, Fri 25, Mon 28
+    Week 4 (Sep 29-Oct 5): Wed 30, Fri 2 (Oct), Mon 5 (Oct)
+    Week 5 (Oct 6-12):  Wed 7, Fri 9, Mon 12
+    Week 6 (Oct 13-19): Wed 14, Fri 16, Mon 19
+    Week 7 (Oct 20-26): Wed 21, Fri 23, Mon 26
+    """
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={0, 2, 4},
+        start_date="2026-09-01", end_date="2026-10-26",
+    )
+    expected = [
+        "2026-09-02", "2026-09-04",
+        "2026-09-07", "2026-09-09", "2026-09-11",
+        "2026-09-14", "2026-09-16", "2026-09-18",
+        "2026-09-21", "2026-09-23", "2026-09-25",
+        "2026-09-28", "2026-09-30", "2026-10-02",
+        "2026-10-05", "2026-10-07", "2026-10-09",
+        "2026-10-12", "2026-10-14", "2026-10-16",
+        "2026-10-19", "2026-10-21", "2026-10-23", "2026-10-26",
+    ]
+    actual = occurrences_between(rule, "2026-09-01", "2026-10-26")
+    assert actual == expected, (
+        f"diff: {set(expected) ^ set(actual)}"
+    )
+
+
+def test_hand_checked_8_week_sequence_weekly_interval_2_mondays() -> None:
+    """8 weeks of a Monday rule at interval 2, anchored Mon 2026-09-07
+    (week 0 = Sep 7-13): fires in weeks 0, 2, 4, 6 -> Mon Sep 7, Mon Sep 21,
+    Mon Oct 5, Mon Oct 19."""
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={0}, interval=2,
+        start_date="2026-09-07", end_date="2026-10-31",
+    )
+    actual = occurrences_between(rule, "2026-09-07", "2026-10-31")
+    assert actual == ["2026-09-07", "2026-09-21", "2026-10-05", "2026-10-19"]
+
+
+def test_custom_days_hand_checked_8_week_sequence() -> None:
+    """8 weeks of a Tue/Thu/Sun rule (1,3,6) anchored Mon 2026-09-07:
+    fires Tue 8, Thu 10, Sun 13, then weekly."""
+    rule = ScheduleRule(
+        rule_type=RuleType.CUSTOM_DAYS, weekday_set={1, 3, 6},
+        start_date="2026-09-07",
+    )
+    # Anchor weeks from Mon Sep 7 (w0 = Sep 7-13 ... w7 = Oct 26-Nov 1):
+    # Tue/Thu/Sun firings per week, 8 weeks fully covered.
+    actual = occurrences_between(rule, "2026-09-07", "2026-11-01")
+    assert actual == [
+        "2026-09-08", "2026-09-10", "2026-09-13",
+        "2026-09-15", "2026-09-17", "2026-09-20",
+        "2026-09-22", "2026-09-24", "2026-09-27",
+        "2026-09-29", "2026-10-01", "2026-10-04",
+        "2026-10-06", "2026-10-08", "2026-10-11",
+        "2026-10-13", "2026-10-15", "2026-10-18",
+        "2026-10-20", "2026-10-22", "2026-10-25",
+        "2026-10-27", "2026-10-29", "2026-11-01",
+    ]
+
+
+def test_weekly_survives_53_week_year_boundary() -> None:
+    """Anchor arithmetic never flips at Jan 1 (the ISO parity trap):
+    a weekly rule spanning New Year keeps its weekday pattern."""
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={3},  # Thursdays
+        start_date="2026-12-24",  # a Thursday
+    )
+    # Thursdays around New Year 2026->2027: Dec 24, 31, Jan 7, 14.
+    assert occurs_on(rule, _d("2026-12-24")) is True
+    assert occurs_on(rule, _d("2026-12-31")) is True
+    assert occurs_on(rule, _d("2027-01-07")) is True
+    assert occurs_on(rule, _d("2027-01-14")) is True
+    # Interleaved days are not Thursdays.
+    assert occurs_on(rule, _d("2027-01-04")) is False  # Monday
+    assert occurs_on(rule, _d("2027-01-05")) is False  # Tuesday
+
+
+def test_weekly_interval_2_across_year_boundary() -> None:
+    """Interval weeks continue across Jan 1 with no parity flip."""
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={4}, interval=2,
+        start_date="2026-12-25",  # a Friday
+    )
+    # Weeks: Dec 25 (w0) fires, Jan 1 (w1) skipped, Jan 8 (w2) fires,
+    # Jan 15 (w3) skipped, Jan 22 (w4) fires.
+    assert occurs_on(rule, _d("2026-12-25")) is True
+    assert occurs_on(rule, _d("2027-01-01")) is False
+    assert occurs_on(rule, _d("2027-01-08")) is True
+    assert occurs_on(rule, _d("2027-01-15")) is False
+    assert occurs_on(rule, _d("2027-01-22")) is True
+
+
+def test_occurrences_between_weekly_disjoint(tmp_path) -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={1},
+        start_date="2026-09-01", end_date="2026-09-30",
+    )
+    assert occurrences_between(rule, "2026-10-01", "2026-10-31") == []
+
+
+def test_occurrences_between_weekly_interval_2_span() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={0}, interval=2,
+        start_date="2026-09-07", end_date="2026-10-31",
+    )
+    result = occurrences_between(rule, "2026-09-01", "2026-10-31")
+    assert result == ["2026-09-07", "2026-09-21", "2026-10-05", "2026-10-19"]
+
+
+def test_occurrences_between_rejects_inverted_bounds() -> None:
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={0}, start_date="2026-09-01"
+    )
+    with pytest.raises(RuleValidationError, match="on or after"):
+        occurrences_between(rule, "2026-10-10", "2026-09-01")
+
+def test_weekly_interval_2_non_monday_anchor_boundary() -> None:
+    """The anchor week is anchored at start_date, NOT a calendar week:
+    a Tuesday-anchored Monday rule fires on Mon Sep 7 (week 0 extends
+    through Sep 7), skips Mon Sep 14 (week 1), fires Mon Sep 21 (week 2)."""
+    rule = ScheduleRule(
+        rule_type=RuleType.WEEKLY, weekday_set={0}, interval=2,
+        start_date="2026-09-01",  # a TUESDAY anchor
+    )
+    # Sep 7 - Sep 1 = 6 days -> week 0 (even): fires.
+    assert occurs_on(rule, _d("2026-09-07")) is True
+    # Sep 14: 13 days -> week 1 (odd): skipped.
+    assert occurs_on(rule, _d("2026-09-14")) is False
+    # Sep 21: 20 days -> week 2 (even): fires.
+    assert occurs_on(rule, _d("2026-09-21")) is True
+    # Sep 28: 27 days -> week 3 (odd): skipped.
+    assert occurs_on(rule, _d("2026-09-28")) is False
+    # Oct 5: 34 days -> week 4 (even): fires.
+    assert occurs_on(rule, _d("2026-10-05")) is True