diff --git a/custom_components/nestquest/dao_instances.py b/custom_components/nestquest/dao_instances.py
index 8c9e852..c948aa8 100644
--- a/custom_components/nestquest/dao_instances.py
+++ b/custom_components/nestquest/dao_instances.py
@@ -47,6 +47,18 @@ from .db import NestQuestDatabase
 _UTC_TIMESTAMP_FORMAT = "%Y-%m-%dT%H:%M:%S+00:00"
 
 
+def _today() -> datetime.date:
+    """Return the current local calendar date (the single date source).
+
+    Every "today" read in this module goes through this one function so
+    the delete clamp and the materialize walk's no-past guard read the
+    same clock, and a caller or test can pin/roll that clock
+    deterministically (e.g. a queued-across-midnight regression).  Pure
+    clock read — no business rule lives here.
+    """
+    return datetime.date.today()
+
+
 def _validate_utc_timestamp(value: str, field: str) -> None:
     """Raise ValueError unless ``value`` is a strict UTC ISO-8601 stamp.
 
@@ -203,7 +215,7 @@ class QuestInstancesDao:
         # check runs after the lock is acquired, because a caller can
         # wait on the lock across midnight — a date that was "today"
         # at call time may be "yesterday" by the time the INSERT runs.
-        today = datetime.date.today().isoformat()
+        today = _today().isoformat()
         if due_date < today:
             raise ValueError(
                 f"instances are never generated in the past: due_date "
@@ -214,7 +226,7 @@ class QuestInstancesDao:
                 # Re-read "today" under the lock: this is the date the
                 # insert actually executes on, so the no-past rule
                 # holds across midnight rollovers.
-                today = datetime.date.today().isoformat()
+                today = _today().isoformat()
                 if due_date < today:
                     raise ValueError(
                         f"instances are never generated in the past: "
@@ -326,7 +338,7 @@ class QuestInstancesDao:
         _validate_window(window)
         # Fail fast on obviously-past dates before queuing on the lock;
         # the authoritative check re-runs under the lock (see upsert).
-        today = datetime.date.today().isoformat()
+        today = _today().isoformat()
         if due_date < today:
             raise ValueError(
                 f"instances are never generated in the past: due_date "
@@ -334,7 +346,7 @@ class QuestInstancesDao:
             )
         async with _connection_lock(self._database):
             async with self._database.transaction():
-                today = datetime.date.today().isoformat()
+                today = _today().isoformat()
                 if due_date < today:
                     raise ValueError(
                         f"instances are never generated in the past: "
@@ -475,7 +487,7 @@ class QuestInstancesDao:
                 # midnight cannot delete instances that became past
                 # while it waited (backdating is clamped to the
                 # execution date, not the call date).
-                today = datetime.date.today().isoformat()
+                today = _today().isoformat()
                 effective_cutoff = max(cutoff_date, today)
                 result = await self._database.execute(
                     "DELETE FROM quest_instances WHERE definition_id = ? "
@@ -487,6 +499,49 @@ class QuestInstancesDao:
                 )
         return result.rowcount
 
+    async def delete_future_uncompleted_for_child(
+        self, child_id: int, cutoff_date: str
+    ) -> tuple[int, str]:
+        """Delete the child's open instances at/after cutoff, across every
+        definition, returning ``(deleted, effective_cutoff)``.
+
+        Child-scoped counterpart to :meth:`delete_future_uncompleted`,
+        used when a child's presence changes (Feature 09): only instances
+        at or after the cutoff with NO completion event are removed, inside
+        one transaction — an instance that gains a completion event
+        mid-flight cannot be deleted.  The cutoff cannot be backdated below
+        today, for the same reason as the definition-scoped method (see its
+        docstring).  Any instance with a completion event is never touched,
+        regardless of its date.
+
+        Returns the number deleted and the effective cutoff that was
+        actually applied (``max(cutoff_date, today)``, read under the
+        lock).  The caller (:func:`~.materialize.regenerate_for_child`)
+        passes that effective cutoff back as its re-materialization anchor,
+        so the delete and the rebuild share ONE execution-day even when the
+        call is queued across midnight — instead of the caller re-reading a
+        stale "today" and materializing a window the delete already
+        superseded.
+        """
+        _validate_date(cutoff_date, "cutoff_date")
+        async with _connection_lock(self._database):
+            async with self._database.transaction():
+                # "today" is read under the lock, matching the
+                # definition-scoped method: the DELETE executes on this
+                # date, so a caller queued across midnight cannot delete
+                # instances that became past while it waited.
+                today = _today().isoformat()
+                effective_cutoff = max(cutoff_date, today)
+                result = await self._database.execute(
+                    "DELETE FROM quest_instances WHERE child_id = ? "
+                    "AND due_date >= ? AND NOT EXISTS ("
+                    "  SELECT 1 FROM completion_events "
+                    "  WHERE instance_id = quest_instances.id"
+                    ")",
+                    (child_id, effective_cutoff),
+                )
+        return result.rowcount, effective_cutoff
+
 
 class CompletionEventsDao:
     """Typed append-only access to the ``completion_events`` table.
diff --git a/custom_components/nestquest/materialize.py b/custom_components/nestquest/materialize.py
index a5e5abf..342e626 100644
--- a/custom_components/nestquest/materialize.py
+++ b/custom_components/nestquest/materialize.py
@@ -37,13 +37,34 @@ window), so re-running the materialization over the same range never
 duplicates a row; a tuple whose instance is already completed is SKIPPED
 (never rewritten, never raised) by
 :meth:`~.dao_instances.QuestInstancesDao.upsert_if_valid`.
+
+Regeneration: a config or presence change must rebuild future instances
+so they track the new state.  :func:`regenerate_for_definition` covers
+definition edits / reassignment (Features 06/07); :func:`regenerate_for_child`
+covers a single child's presence change (Feature 09).  Both delete the
+affected open instances at or after today — never a completed instance,
+never the past — and re-run the walk over the rolling horizon
+``[today, today + DEFAULT_HORIZON_DAYS]``.
+
+HOOK (Feature 09 presence services): the presence business layer that
+lands in Feature 09 MUST call :func:`regenerate_for_child` after EVERY
+presence-state write so a child's future instances track its presence:
+``set_presence_pattern`` (including clearing/setting an empty pattern),
+deleting/clearing the presence schedule
+(:meth:`~.dao_presence.PresenceSchedulesDao.delete`),
+``create_presence_override``, and ``delete_presence_override``.  A
+schedule delete changes presence state too (the child becomes
+always-present), so it must regenerate just like the others.  This hook
+is documented, not yet wired: no presence business layer exists yet, and
+the presence DAO (``dao_presence.py``) must stay free of business rules
+— never call :func:`regenerate_for_child` from inside the DAO layer.
 """
 from __future__ import annotations
 
 import datetime
 
 from .const import DEFAULT_HORIZON_DAYS
-from .dao_instances import QuestInstancesDao
+from .dao_instances import QuestInstancesDao, _today
 from .dao_rules import (
     _validate_date,
     load_materialization_input,
@@ -104,6 +125,8 @@ async def materialize(
     database: NestQuestDatabase,
     start_date: str,
     end_date: str,
+    *,
+    child_ids: list[int] | None = None,
 ) -> int:
     """Generate quest instances for the closed range [start_date, end_date].
 
@@ -113,6 +136,12 @@ async def materialize(
     of instances upserted for the range (idempotent — a re-run refreshes
     the same rows, never duplicates them).
 
+    ``child_ids`` optionally scopes the walk to exactly those children:
+    assignees outside the list are never written, so a caller that only
+    wants one child's instances rebuilt (e.g. :func:`regenerate_for_child`
+    after a presence change) cannot touch any unrelated child's rows.
+    When omitted (or None) the walk covers every assignee as before.
+
     All inputs are read in ONE locked transaction; each tuple's write then
     goes through the atomic :meth:`~.dao_instances.QuestInstancesDao.upsert_if_valid`,
     which re-validates the tuple and its current ``due_time`` in the same
@@ -132,6 +161,7 @@ async def materialize(
         load_materialization_input(database, start_date, end_date)
     )
     engine = _build_engine(schedules_records, overrides_records)
+    child_filter = None if child_ids is None else set(child_ids)
 
     definitions = [
         (snapshot.definition.id, _decode_rule(snapshot),
@@ -153,6 +183,8 @@ async def materialize(
             if not occurs_on(rule, cursor):
                 continue
             for child in assignees:
+                if child_filter is not None and child.id not in child_filter:
+                    continue
                 if not engine.is_present(child.id, cursor):
                     continue
                 for window in windows:
@@ -186,17 +218,85 @@ async def regenerate_for_definition(
     assignee set and windows re-materialize against today's state.
 
     "today" is computed the same way the walk computes it —
-    ``datetime.date.today()`` — so the delete cutoff and the
+    :func:`~.dao_instances._today` — so the delete cutoff and the
     re-materialization range share one anchor, and the walk's
     ``upsert_if_valid`` no-past guard never rejects the regenerated
     range.  Returns the number of instances the re-materialization
     upserted across the whole snapshot (idempotent — other active
     definitions' tuples refresh in place, never duplicate).
     """
-    today = datetime.date.today()
+    today = _today()
     start_date = today.isoformat()
     end_date = (today + datetime.timedelta(days=DEFAULT_HORIZON_DAYS)).isoformat()
 
     instances = QuestInstancesDao(database)
     await instances.delete_future_uncompleted(definition_id, start_date)
     return await materialize(database, start_date, end_date)
+
+
+# HOOK (Feature 09 presence services): ``regenerate_for_child`` is the
+# child-presence counterpart to ``regenerate_for_definition``.  The
+# presence business layer that lands in Feature 09 MUST call
+# ``regenerate_for_child`` after EVERY presence-state write, so future
+# instances track a child's changed presence: set_presence_pattern
+# (including clearing/setting an empty pattern), deleting/clearing the
+# presence schedule (PresenceSchedulesDao.delete),
+# create_presence_override, and delete_presence_override.  A schedule
+# delete changes presence state too (the child becomes always-present),
+# so it must regenerate just like the others.  It is deliberately NOT
+# wired into ``dao_presence.py``: the DAO layer stays pure storage (no
+# business rules), and no presence business layer exists yet to host the
+# call — see the module docstring note above.
+async def regenerate_for_child(
+    database: NestQuestDatabase,
+    child_id: int,
+) -> int:
+    """Regenerate a child's future instances after a presence change.
+
+    The Feature 09 presence services call this after every
+    presence-state write — set_presence_pattern (including clearing or
+    setting an empty pattern), deleting/clearing the presence schedule
+    (:meth:`~.dao_presence.PresenceSchedulesDao.delete`),
+    create_presence_override, and delete_presence_override — so a
+    child's future instances track its new presence: the child's open
+    instances at or after today are deleted across ALL its definitions
+    (never a completed instance, never the past) via
+    :meth:`~.dao_instances.QuestInstancesDao.delete_future_uncompleted_for_child`,
+    then the materialization walk re-runs over the rolling horizon
+    ``[today, today + DEFAULT_HORIZON_DAYS]`` scoped to that child only,
+    so the child's now-absent/present dates re-materialize against
+    today's presence WITHOUT touching any other child's rows.
+
+    ``child_id`` must be a plain int — bool and float are rejected
+    (SQLite binds a bool as 0/1 and a float would round, so a malformed
+    id must never mutate the wrong profile).
+
+    "today" is computed the same way the walk computes it —
+    :func:`~.dao_instances._today` — and the re-materialization range uses the
+    delete's returned effective cutoff (see
+    :meth:`~.dao_instances.QuestInstancesDao.delete_future_uncompleted_for_child`),
+    so the delete cutoff and the re-materialization window share ONE
+    execution-day anchor even when the call is queued across midnight.
+    Returns the number of instances the re-materialization upserted for
+    the child across the whole snapshot.
+    """
+    if isinstance(child_id, bool) or not isinstance(child_id, int):
+        raise ValueError(f"child_id must be an integer, got {child_id!r}")
+
+    today = _today()
+
+    instances = QuestInstancesDao(database)
+    # Use the delete's returned effective cutoff as the materialize anchor,
+    # NOT the independently-computed "today" above.  If the call is queued
+    # across midnight the delete clamps its cutoff to the execution-day;
+    # materializing from the stale "today" (now yesterday) would trip the
+    # walk's no-past guard and leave the child's future instances deleted
+    # but not rebuilt.  One anchor for both keeps them consistent.
+    _, effective_cutoff = await instances.delete_future_uncompleted_for_child(
+        child_id, today.isoformat()
+    )
+    start = datetime.date.fromisoformat(effective_cutoff)
+    end_date = (start + datetime.timedelta(days=DEFAULT_HORIZON_DAYS)).isoformat()
+    return await materialize(
+        database, start.isoformat(), end_date, child_ids=[child_id]
+    )
diff --git a/tests/test_materialize.py b/tests/test_materialize.py
index e114678..62523fd 100644
--- a/tests/test_materialize.py
+++ b/tests/test_materialize.py
@@ -19,6 +19,7 @@ from custom_components.nestquest.dao_rules import (
 from custom_components.nestquest.db import NestQuestDatabase
 from custom_components.nestquest.materialize import (
     materialize,
+    regenerate_for_child,
     regenerate_for_definition,
 )
 from custom_components.nestquest.migrations import apply_migrations
@@ -772,4 +773,271 @@ def test_edit_quest_definition_regenerates_future_instances(tmp_path) -> None:
             assert (day.isoformat() in by_due) == occurs_on(weekly, day)
         return None
 
-    _with_db(tmp_path, "edit-regenerates.db")(_body)
\ No newline at end of file
+    _with_db(tmp_path, "edit-regenerates.db")(_body)
+
+
+def test_regenerate_for_child_rebuilds_horizon_preserves_history(
+    tmp_path,
+) -> None:
+    async def _body(database):
+        from custom_components.nestquest.dao_presence import (
+            PresenceOverridesDao,
+        )
+
+        children = ChildrenDao(database)
+        overrides = PresenceOverridesDao(database)
+        child = await children.create("Ada", NOW)
+
+        today = datetime.date.today()
+        horizon_end = today + datetime.timedelta(days=14)
+        start_iso = today.isoformat()
+
+        created = await create_quest_definition(
+            database,
+            "Daily chore",
+            ScheduleRule(rule_type=RuleType.DAILY, start_date=start_iso),
+            [child.id],
+            [("morning", "09:00")],
+        )
+
+        dao = QuestInstancesDao(database)
+        events = CompletionEventsDao(database)
+
+        # Instances across the full horizon: 15 daily rows.
+        await materialize(database, start_iso, horizon_end.isoformat())
+        all_future = await dao.list_by_date_range(
+            child.id, start_iso, horizon_end.isoformat()
+        )
+        assert len(all_future) == 15
+
+        # A completed instance on tomorrow: immutable, must be spared.
+        completed_due = (today + datetime.timedelta(days=1)).isoformat()
+        completed = next(r for r in all_future if r.due_date == completed_due)
+        await events.append(
+            completed.id,
+            child.id,
+            "completed",
+            "user",
+            f"{completed_due}T08:00:00+00:00",
+            True,
+            actor_user_id="user-1",
+        )
+
+        # A past instance (yesterday): raw insert bypasses the walk's
+        # no-past guard so the child-scoped delete has history to spare.
+        past_due = (today - datetime.timedelta(days=1)).isoformat()
+        await database.execute(
+            "INSERT INTO quest_instances (definition_id, child_id, "
+            "window, due_date, due_time, generated_at) "
+            "VALUES (?, ?, 'morning', ?, '09:00', ?)",
+            (created.definition.id, child.id, past_due, NOW),
+        )
+
+        # An ABSENT override covering three future dates that had
+        # instances: days 2..4 after today.
+        absent_start = (today + datetime.timedelta(days=2)).isoformat()
+        absent_end = (today + datetime.timedelta(days=4)).isoformat()
+        override = await overrides.create(
+            child.id, absent_start, absent_end, False, note="away"
+        )
+
+        await regenerate_for_child(database, child.id)
+
+        records = await dao.list_by_date_range(
+            child.id, past_due, horizon_end.isoformat()
+        )
+        by_due = {r.due_date: r for r in records}
+
+        # The now-absent days' instances are gone.
+        for offset in range(2, 5):
+            iso = (today + datetime.timedelta(days=offset)).isoformat()
+            assert iso not in by_due
+
+        # The completed instance survived untouched (same physical id).
+        assert by_due[completed_due].id == completed.id
+
+        # The past instance survived.
+        assert past_due in by_due
+
+        # Every non-absent future day still has its instance.
+        for offset in range(15):
+            iso = (today + datetime.timedelta(days=offset)).isoformat()
+            if 2 <= offset <= 4:
+                continue
+            assert iso in by_due
+
+        # Remove the override and regenerate again: the absent days return.
+        await overrides.delete(override.id)
+        await regenerate_for_child(database, child.id)
+
+        records = await dao.list_by_date_range(
+            child.id, past_due, horizon_end.isoformat()
+        )
+        by_due = {r.due_date: r for r in records}
+
+        for offset in range(15):
+            iso = (today + datetime.timedelta(days=offset)).isoformat()
+            assert iso in by_due
+
+        # The completed instance is still the same untouched row, and the
+        # past instance is still there.
+        assert by_due[completed_due].id == completed.id
+        assert by_due[completed_due].due_time == "09:00"
+        assert past_due in by_due
+        return None
+
+    _with_db(tmp_path, "regenerate-child.db")(_body)
+
+
+def test_regenerate_for_child_uses_single_anchor_across_midnight(
+    tmp_path, monkeypatch
+) -> None:
+    """A call queued across midnight must not delete-then-fail-to-rebuild.
+
+    ``regenerate_for_child`` reads "today" once as a cutoff hint, but the
+    delete clamps that cutoff to the execution-day under its own lock and
+    RETURNS the effective cutoff; the re-materialization window is then
+    anchored to the same returned day.  This test fakes a midnight rollover
+    between the two reads: the caller's hint is day0 while the delete
+    executes on day1.  The rebuild must start on day1 (so the walk's
+    no-past guard never fires) and the now-past day0 instance must survive.
+    """
+    day0 = datetime.date.today() + datetime.timedelta(days=30)
+    day1 = day0 + datetime.timedelta(days=1)
+
+    clock = {"rolled": False, "reads": 0}
+
+    def _fake_today() -> datetime.date:
+        if not clock["rolled"]:
+            return day0
+        clock["reads"] += 1
+        return day0 if clock["reads"] == 1 else day1
+
+    import custom_components.nestquest.dao_instances as dao_instances_module
+    import custom_components.nestquest.materialize as materialize_module
+
+    monkeypatch.setattr(dao_instances_module, "_today", _fake_today)
+    monkeypatch.setattr(materialize_module, "_today", _fake_today)
+
+    async def _body(database):
+        children = ChildrenDao(database)
+        child = await children.create("Ada", NOW)
+
+        day0_iso = day0.isoformat()
+        horizon_end = day0 + datetime.timedelta(days=14)
+
+        created = await create_quest_definition(
+            database,
+            "Daily chore",
+            ScheduleRule(rule_type=RuleType.DAILY, start_date=day0_iso),
+            [child.id],
+            [("morning", "09:00")],
+        )
+        dao = QuestInstancesDao(database)
+
+        # Seed the horizon while the clock reads day0.
+        await materialize(database, day0_iso, horizon_end.isoformat())
+
+        # Roll the clock forward: every read after the caller's single
+        # cutoff hint now returns day1 (the delete's execution-day).
+        clock["rolled"] = True
+        clock["reads"] = 0
+
+        rebuilt = await regenerate_for_child(database, child.id)
+
+        # No raise occurred; the rebuilt window is anchored on the delete's
+        # execution-day (day1), so day1..day1+14 all exist.
+        assert rebuilt == 15
+        day1_iso = day1.isoformat()
+        day1_horizon_end = day1 + datetime.timedelta(days=14)
+        assert len(await dao.list_by_date_range(
+            child.id, day1_iso, day1_horizon_end.isoformat()
+        )) == 15
+
+        # day0 was the caller's "today" but rolled over to the past by the
+        # time the delete ran; it must survive (never delete the past).
+        assert await dao.get(
+            created.definition.id, child.id, day0_iso, "morning"
+        ) is not None
+        return rebuilt
+
+    _with_db(tmp_path, "regenerate-child-midnight.db")(_body)
+
+
+def test_regenerate_for_child_is_child_scoped(tmp_path) -> None:
+    """Regenerating one child must never touch another child's rows."""
+    async def _body(database):
+        from custom_components.nestquest.dao_presence import (
+            PresenceOverridesDao,
+        )
+
+        children = ChildrenDao(database)
+        overrides = PresenceOverridesDao(database)
+        a = await children.create("Ada", NOW)
+        b = await children.create("Bo", NOW)
+
+        today = datetime.date.today()
+        horizon_end = today + datetime.timedelta(days=14)
+        start_iso = today.isoformat()
+
+        await create_quest_definition(
+            database,
+            "Daily chore",
+            ScheduleRule(rule_type=RuleType.DAILY, start_date=start_iso),
+            [a.id, b.id],
+            [("morning", "09:00")],
+        )
+
+        dao = QuestInstancesDao(database)
+        await materialize(database, start_iso, horizon_end.isoformat())
+
+        # Baseline for child b, keyed by due_date, so we can prove its rows
+        # are byte-for-byte unchanged afterward.
+        baseline_b = {
+            r.due_date: (r.id, r.due_time, r.generated_at)
+            for r in await dao.list_by_date_range(
+                b.id, start_iso, horizon_end.isoformat()
+            )
+        }
+        assert len(baseline_b) == 15
+
+        # An ABSENT override for child a only, covering days 2..4.
+        absent_start = (today + datetime.timedelta(days=2)).isoformat()
+        absent_end = (today + datetime.timedelta(days=4)).isoformat()
+        await overrides.create(
+            a.id, absent_start, absent_end, False, note="away"
+        )
+
+        await regenerate_for_child(database, a.id)
+
+        # Child a's now-absent days vanished.
+        a_by_due = {
+            r.due_date: r
+            for r in await dao.list_by_date_range(
+                a.id, start_iso, horizon_end.isoformat()
+            )
+        }
+        for offset in range(2, 5):
+            iso = (today + datetime.timedelta(days=offset)).isoformat()
+            assert iso not in a_by_due
+
+        # Child b is untouched: same physical rows, same snapshot columns.
+        b_records = await dao.list_by_date_range(
+            b.id, start_iso, horizon_end.isoformat()
+        )
+        assert len(b_records) == 15
+        for r in b_records:
+            assert (r.id, r.due_time, r.generated_at) == baseline_b[r.due_date]
+        return None
+
+    _with_db(tmp_path, "regenerate-child-scoped.db")(_body)
+
+
+def test_regenerate_for_child_rejects_non_int_child_id(tmp_path) -> None:
+    async def _body(database):
+        for bad in (True, False, 1.0, "1"):
+            with pytest.raises(ValueError, match="child_id must be an integer"):
+                await regenerate_for_child(database, bad)
+        return None
+
+    _with_db(tmp_path, "regenerate-child-badid.db")(_body)
\ No newline at end of file