diff --git a/api/nestquest_core.py b/api/nestquest_core.py
index d67596a..5cfb60d 100644
--- a/api/nestquest_core.py
+++ b/api/nestquest_core.py
@@ -129,6 +129,17 @@ core_events = importlib.import_module(f"{_CORE_MODULE_NAME}.events")
 #: the snapshot builder's ``settings`` parameter takes.
 core_settings = importlib.import_module(f"{_CORE_MODULE_NAME}.settings")
 
+#: The durable settings store (``core.settings_store.load_settings`` /
+#: ``update_settings``) the admin plane's settings routes read and
+#: write — the API's OWN settings source: a validated JSON document in
+#: the existing ``nestquest_meta_state`` table, resolved through the
+#: same core settings validators (the integration's HA config-entry
+#: options remain a temporary separate source until Feature 18 wires
+#: the client to the API).
+core_settings_store = importlib.import_module(
+    f"{_CORE_MODULE_NAME}.settings_store"
+)
+
 #: The children business layer (``core.children.create_child`` et al.)
 #: the admin plane's children routes call.
 core_children = importlib.import_module(f"{_CORE_MODULE_NAME}.children")
@@ -206,4 +217,5 @@ __all__ = [
     "core_recurrence",
     "core_snapshot",
     "core_settings",
+    "core_settings_store",
 ]
diff --git a/api/routes_admin.py b/api/routes_admin.py
index 4ff4553..6c8ff9a 100644
--- a/api/routes_admin.py
+++ b/api/routes_admin.py
@@ -116,6 +116,29 @@ owns every rule so the two routes cannot drift:
   a ``Content-Disposition`` attachment filename and the documented,
   stable header row (Admin spec §5 event-row fields).
 
+The settings routes (task 2b3de7e5) follow the same pattern over
+:mod:`nestquest_core.settings_store` — the API's OWN durable settings
+store.  The API now OWNS settings in the database (a validated JSON
+document in the existing ``nestquest_meta_state`` key/value table); the
+integration's Home-Assistant config-entry options remain a temporary,
+SEPARATE source until Feature 18 wires the client to the API — the two
+are deliberately not unified here:
+
+- ``GET /settings`` returns the current effective settings: all ten
+  documented fields (the rolling horizon, the day rollover time, the
+  notify target, the three notification times and the four enable
+  toggles) — the defaults on a fresh database.
+- ``PATCH /settings`` updates ONLY the supplied fields: the body is a
+  JSON object of settings field names to new values, passed STRAIGHT
+  to :func:`nestquest_core.settings_store.update_settings` — the
+  unknown-field rejection, the per-field validation (the core settings
+  validators: a positive int, strict ``HH:MM`` strings, real booleans)
+  and the validate-everything-before-write atomicity all live in the
+  core, so a rejected update never changes the stored settings.  A
+  JSON ``null`` value resets its field to the default (the settings
+  module's uniform None-as-absent rule).  The response is the updated
+  effective settings, the same shape ``GET`` returns.
+
 Error mapping (every children, quest-definition and presence route,
 deliberately narrow):
 
@@ -174,6 +197,13 @@ deliberately narrow):
   invalid, the same failure class Pydantic reports.  Only
   ``ValueError`` is caught, so an unexpected failure re-raises rather
   than becoming a 4xx.
+- The SETTINGS routes have no path ids either, so they have no 404
+  case: a body that is not a JSON object is FastAPI's 422 before any
+  handler code runs, and every core ``ValueError`` — an unknown field
+  or an invalid value, each naming the offending field, raised BEFORE
+  any write so the stored settings are never half-changed — is 422
+  (:func:`_raise_settings_error`).  Only ``ValueError`` is caught, so
+  an unexpected failure re-raises rather than becoming a 4xx.
 
 PATCH edit semantics: the body model's fields are optional and only
 SUPPLIED fields are forwarded (``model_dump(exclude_unset=True)``), so
@@ -205,6 +235,8 @@ from api.nestquest_core import (
     core_presence_management,
     core_quest_definitions,
     core_recurrence,
+    core_settings,
+    core_settings_store,
 )
 
 #: All admin-plane routes share this router; the ONE admin dependency
@@ -601,6 +633,27 @@ class AdminHistoryResponse(BaseModel):
     rows: list[AdminHistoryRow]
 
 
+class AdminSettingsResponse(BaseModel):
+    """The effective settings as the admin plane serializes them.
+
+    Mirrors the core :class:`~nestquest_core.settings.NestQuestSettings`
+    — all TEN documented fields, resolved (every absent stored field
+    already fell back to its default in the core).  The same shape both
+    the GET and the PATCH route answer with.
+    """
+
+    horizon_days: int
+    day_rollover_time: str
+    notify_target: str
+    morning_summary_time: str
+    afternoon_reminder_time: str
+    end_of_day_report_time: str
+    morning_summary_enabled: bool
+    afternoon_reminder_enabled: bool
+    end_of_day_report_enabled: bool
+    celebration_enabled: bool
+
+
 #: 404 detail for a child id the core layer reports as non-existent.
 _CHILD_NOT_FOUND_DETAIL = "Child not found"
 
@@ -736,6 +789,20 @@ def _raise_history_error(error: ValueError) -> NoReturn:
     raise HTTPException(status_code=422, detail=str(error)) from error
 
 
+def _raise_settings_error(error: ValueError) -> NoReturn:
+    """Map a core settings-store ``ValueError`` onto 422 and raise it.
+
+    The settings routes have no path ids either, so they have no 404
+    case: every ``ValueError`` that survives to here is a rejected
+    change — an unknown field or an invalid value, each raised by the
+    core naming the offending field BEFORE any write, so the stored
+    settings are never half-changed — and is 422 with the core's
+    message as the detail.  Only ``ValueError`` is caught, so an
+    unexpected failure re-raises rather than becoming a 4xx.
+    """
+    raise HTTPException(status_code=422, detail=str(error)) from error
+
+
 def _local_now() -> datetime.datetime:
     """Return the API host's local time as ONE timezone-aware clock read.
 
@@ -1401,6 +1468,29 @@ def _history_row_response(row: core_history.HistoryRow) -> AdminHistoryRow:
     )
 
 
+def _settings_response(
+    settings: core_settings.NestQuestSettings,
+) -> AdminSettingsResponse:
+    """Serialize one core NestQuestSettings into the documented payload.
+
+    Explicit field-by-field (not ``dataclasses.asdict``) so the payload
+    stays pinned to the ten documented fields even if the core
+    dataclass later grows another one.
+    """
+    return AdminSettingsResponse(
+        horizon_days=settings.horizon_days,
+        day_rollover_time=settings.day_rollover_time,
+        notify_target=settings.notify_target,
+        morning_summary_time=settings.morning_summary_time,
+        afternoon_reminder_time=settings.afternoon_reminder_time,
+        end_of_day_report_time=settings.end_of_day_report_time,
+        morning_summary_enabled=settings.morning_summary_enabled,
+        afternoon_reminder_enabled=settings.afternoon_reminder_enabled,
+        end_of_day_report_enabled=settings.end_of_day_report_enabled,
+        celebration_enabled=settings.celebration_enabled,
+    )
+
+
 @router.get(
     "/history",
     summary="Query the completion history for one filter and range",
@@ -1489,4 +1579,60 @@ async def admin_history_csv(
     )
 
 
+@router.get(
+    "/settings",
+    summary="Read the effective settings",
+    response_model=AdminSettingsResponse,
+)
+async def admin_get_settings(request: Request) -> AdminSettingsResponse:
+    """Return the current effective settings (all ten documented fields).
+
+    Requires a valid admin JWT (the router's shared
+    :func:`~api.auth.require_admin` dependency — the ONE check; this
+    handler performs NO auth of its own).  Thin adapter: ONE
+    :func:`nestquest_core.settings_store.load_settings` call — the API
+    owns settings in the database (the integration's HA options remain
+    a temporary separate source until Feature 18 wires the client to
+    the API), and the stored-document decode, the per-field validation
+    and the defaults-for-absent-fields fallback all live in the core.
+    A corrupt stored document never fails the read: the core falls
+    back to the defaults (per field where possible).
+    """
+    state: DatabaseState = request.app.state.db
+    settings = await core_settings_store.load_settings(state.database)
+    return _settings_response(settings)
+
+
+@router.patch(
+    "/settings",
+    summary="Update the supplied settings fields",
+    response_model=AdminSettingsResponse,
+)
+async def admin_update_settings(
+    changes: dict[str, object], request: Request
+) -> AdminSettingsResponse:
+    """Update the supplied settings fields and return the new state.
+
+    Requires a valid admin JWT (the router's shared
+    :func:`~api.auth.require_admin` dependency — the ONE check; this
+    handler performs NO auth of its own).  Thin adapter: the body — a
+    JSON object of settings field names to new values — goes STRAIGHT
+    to :func:`nestquest_core.settings_store.update_settings`, which
+    rejects an unknown field, resolves each supplied field through the
+    core settings validators (a JSON ``null`` resets its field to the
+    default) and merges onto the current effective settings only after
+    every value has validated — so a rejected update never changes the
+    stored settings.  Every core ``ValueError`` is 422
+    (:func:`_raise_settings_error`); anything else re-raises.
+    """
+    state: DatabaseState = request.app.state.db
+    try:
+        settings = await core_settings_store.update_settings(
+            state.database, changes
+        )
+    except ValueError as error:
+        _raise_settings_error(error)
+    return _settings_response(settings)
+
+
 __all__ = ["router"]
diff --git a/custom_components/nestquest/core/settings_store.py b/custom_components/nestquest/core/settings_store.py
new file mode 100644
index 0000000..9f9c91f
--- /dev/null
+++ b/custom_components/nestquest/core/settings_store.py
@@ -0,0 +1,210 @@
+"""Durable settings store for the NestQuest API service.
+
+The API service has NO Home Assistant config entry, so it cannot build
+:class:`~.settings.NestQuestSettings` from ``entry.options`` the way the
+integration does.  This module gives the API its own durable settings
+source: a JSON document kept in the EXISTING ``nestquest_meta_state``
+key/value table (:class:`~.dao_meta.MetaStateDao`) under the well-known
+key :data:`SETTINGS_META_KEY` — no schema change, no new table —
+validated through the SAME field table the settings object is built
+from (:data:`~.settings._FIELDS`, the table driving
+``from_options``/``from_options_resilient``).  No validation rule is
+re-implemented here.
+
+OWNERSHIP: the API now owns settings in the database.  The
+integration's Home-Assistant config-entry options remain a temporary,
+SEPARATE source until Feature 18 converts the integration into a thin
+API client; the two are deliberately NOT unified here, and neither
+side reads the other's values.
+
+STORED SERIALIZATION — the document at ``SETTINGS_META_KEY`` is a JSON
+object holding exactly the TEN settings fields, keyed by field name
+(which equals the ``CONF_*`` option key for every field), complete
+after the first update:
+
+- ``horizon_days`` — int >= 1,
+- ``day_rollover_time``, ``morning_summary_time``,
+  ``afternoon_reminder_time``, ``end_of_day_report_time`` — strict
+  24-hour ``HH:MM`` strings,
+- ``notify_target`` — a string (a padded value is stripped by the
+  core's normalizer),
+- ``morning_summary_enabled``, ``afternoon_reminder_enabled``,
+  ``end_of_day_report_enabled``, ``celebration_enabled`` — real
+  booleans.
+
+Only values whose core validators ACCEPTED are ever written, so a
+stored document always round-trips through the core's option builders.
+An absent key (a fresh database) resolves to the all-defaults
+settings, and a corrupt document degrades to defaults or per-field
+defaults rather than crashing the service (see :func:`load_settings`).
+"""
+from __future__ import annotations
+
+import asyncio
+import json
+from collections.abc import Mapping
+from typing import Any
+
+from .const import LOGGER
+from .dao_meta import MetaStateDao
+from .db import NestQuestDatabase
+from .settings import NestQuestSettings, _FIELDS
+
+#: The well-known ``nestquest_meta_state`` key holding the settings
+#: document.  One key, one JSON object — the same table the missed
+#: sweep's watermark already uses, so no migration is needed.
+SETTINGS_META_KEY = "settings"
+
+#: The per-field resolution table keyed by field name: each row is the
+#: ``(default, validator)`` pair the settings module's ``_FIELDS`` table
+#: carries for that field.  ``update_settings`` resolves each PROVIDED
+#: field through its row's validator — the SAME core validators
+#: ``from_options`` applies — and never re-implements one here.
+#: (Field names equal the ``CONF_*`` option keys, so one dict serves
+#: both the API's field names and the stored document's keys.)
+_RESOLUTIONS: dict[str, tuple[Any, Any]] = {
+    key: (default, validator) for _field, key, default, validator in _FIELDS
+}
+
+#: The known field names, in the settings module's field order — the
+#: allowed keys of an update body and the stored document's key set.
+_FIELD_NAMES: tuple[str, ...] = tuple(
+    key for _field, key, _default, _validator in _FIELDS
+)
+
+#: One asyncio.Lock per (connection wrapper, running loop), the missed
+#: sweep's pattern: the whole stored-document read → merge → write span
+#: is one critical section, so two concurrent updates queue instead of
+#: one losing the other's change — the loser re-reads the document
+#: INSIDE the lock and merges onto the winner's settings.
+_SETTINGS_LOCKS: dict[tuple[int, int], asyncio.Lock] = {}
+
+
+def _settings_lock(database: NestQuestDatabase) -> asyncio.Lock:
+    """Return the settings lock bound to ``database``'s running loop."""
+    loop = asyncio.get_running_loop()
+    key = (id(database), id(loop))
+    lock = _SETTINGS_LOCKS.get(key)
+    if lock is None:
+        lock = asyncio.Lock()
+        _SETTINGS_LOCKS[key] = lock
+    return lock
+
+
+async def _load_document(database: NestQuestDatabase) -> dict[str, Any]:
+    """Read and decode the stored settings document (empty when unusable).
+
+    An absent key — a fresh database that never updated settings — and
+    an unparseable value (invalid JSON, or JSON that is not an object)
+    return an empty mapping, which the option builders resolve to the
+    all-defaults settings; the corrupt cases log a warning first.  A
+    parseable object is returned as stored (its per-field validity is
+    the builder's concern, not this reader's).
+    """
+    raw = await MetaStateDao(database).get(SETTINGS_META_KEY)
+    if raw is None:
+        return {}
+    try:
+        document = json.loads(raw)
+    except ValueError:
+        LOGGER.warning(
+            "NestQuest stored settings (meta_state key %r) are not valid "
+            "JSON; falling back to the default settings",
+            SETTINGS_META_KEY,
+        )
+        return {}
+    if not isinstance(document, dict):
+        LOGGER.warning(
+            "NestQuest stored settings (meta_state key %r) are not a JSON "
+            "object; falling back to the default settings",
+            SETTINGS_META_KEY,
+        )
+        return {}
+    return document
+
+
+def _named(field: str, error: ValueError) -> str:
+    """Return a field-named message for a rejected validator value.
+
+    The horizon, time and notify-target validators already name their
+    field in the message; the boolean validator's message is generic
+    (``expected a boolean, got ...``), so it gets the field prefixed.
+    Every rejected update's error therefore names its field either way.
+    """
+    message = str(error)
+    if message.startswith(f"{field} "):
+        return message
+    return f"{field}: {message}"
+
+
+async def load_settings(database: NestQuestDatabase) -> NestQuestSettings:
+    """Return the current effective settings stored for ``database``.
+
+    Reads :data:`SETTINGS_META_KEY` and resolves the stored document
+    through the core settings validators, with each absent field
+    falling back to its default.  An absent key and an unparseable
+    document fall back to the all-defaults settings (via
+    :func:`_load_document`), and a parseable document with a single
+    invalid FIELD falls back PER FIELD — through
+    :meth:`NestQuestSettings.from_options_resilient`, the core's own
+    resilient builder — so a corrupt sibling never resets the stored
+    values around it.  This never raises: the service must keep
+    serving reads even over a corrupt store.
+    """
+    document = await _load_document(database)
+    return NestQuestSettings.from_options_resilient(document)
+
+
+async def update_settings(
+    database: NestQuestDatabase, changes: Mapping[str, Any]
+) -> NestQuestSettings:
+    """Validate ``changes`` and persist them as the effective settings.
+
+    ``changes`` maps settings field names to new values.  EVERY name is
+    checked against the known field table BEFORE anything is validated
+    or written: an unknown name raises a ``ValueError`` naming it (and
+    the known names), leaving the stored settings untouched.  Each
+    PROVIDED field is then resolved from_options-style — its
+    :data:`~.settings._FIELDS` validator applied, with a JSON ``null``
+    mapping to the field's default (the settings module's uniform
+    None-as-absent rule) — and an invalid value raises a ``ValueError``
+    naming the field, also BEFORE anything is written, so a rejected
+    update can never leave a half-applied document behind.
+
+    The validated changes are merged onto the current effective
+    settings and the merged (complete, ten-field) document is persisted
+    in one atomic upsert; the updated settings are returned.  The whole
+    read → merge → write span runs inside the per-database settings
+    lock, so concurrent updates queue instead of interleaving.
+    """
+    if not isinstance(changes, Mapping):
+        raise ValueError(
+            "settings changes must be a JSON object mapping field names "
+            "to values"
+        )
+    unknown = sorted(
+        str(name) for name in changes if name not in _RESOLUTIONS
+    )
+    if unknown:
+        listed = ", ".join(repr(name) for name in unknown)
+        known = ", ".join(_FIELD_NAMES)
+        raise ValueError(
+            f"unknown settings field(s): {listed}; known fields: {known}"
+        )
+    async with _settings_lock(database):
+        current = await load_settings(database)
+        document: dict[str, Any] = {
+            field: getattr(current, field) for field in _FIELD_NAMES
+        }
+        for name, raw_value in changes.items():
+            default, validator = _RESOLUTIONS[name]
+            try:
+                document[name] = validator(
+                    default if raw_value is None else raw_value
+                )
+            except ValueError as error:
+                raise ValueError(_named(name, error)) from error
+        await MetaStateDao(database).set(
+            SETTINGS_META_KEY, json.dumps(document, sort_keys=True)
+        )
+    return NestQuestSettings(**document)
diff --git a/tests/test_api_admin_settings.py b/tests/test_api_admin_settings.py
new file mode 100644
index 0000000..94604a1
--- /dev/null
+++ b/tests/test_api_admin_settings.py
@@ -0,0 +1,398 @@
+"""Admin-plane settings route tests (task 2b3de7e5).
+
+These tests exercise the admin plane's settings read and update routes
+against the ASGI app with httpx, reusing the shared local-RSA-key/
+stubbed-JWKS harness (:mod:`tests.admin_jwt_harness`) so an admin JWT
+genuinely authenticates — signature, issuer, audience, expiry and the
+nestquest-admins group — with NO network access.  The stored settings
+document is read back through the SAME core copy the app uses
+(``nestquest_core.*``; see the two-copy caveat in api/nestquest_core.py)
+via its :class:`nestquest_core.dao_meta.MetaStateDao`, so persistence is
+proven against the DATABASE the routes wrote, not a parallel copy.
+
+Proven per the done-condition, everything read back through the API:
+
+- ``GET /api/v1/admin/settings`` returns the current effective settings
+  — the ten documented fields at their defaults on a fresh database.
+- ``PATCH /api/v1/admin/settings`` PERSISTS the supplied fields and the
+  NEXT read reflects them; a later partial update merges onto the
+  current effective settings (omitted fields keep their stored value),
+  and the document is stored under the well-known ``nestquest_meta_state``
+  key.
+- An invalid value (a non-positive or boolean horizon, a non-strict
+  time, a non-bool toggle, a non-string target) is rejected with 422
+  naming the field, and the stored settings are UNCHANGED — the next
+  read still shows the previous value.  An unknown field is rejected
+  the same way, also when mixed with a valid field (validate
+  everything before writing).
+- A corrupt stored document (invalid JSON, a non-object, an invalid
+  field value) does not crash the service: the read falls back to the
+  defaults, per field where possible.
+- Authentication runs through the router's ONE ``require_admin``
+  dependency: a non-admin JWT is 403 and an absent credential is 401
+  on both routes — and no refused patch writes anything.
+"""
+from __future__ import annotations
+
+import importlib
+import json
+from types import SimpleNamespace
+
+import pytest
+
+from tests.admin_jwt_harness import (
+    ADMIN_KEY,
+    KID,
+    AdminRunner,
+    jwks_for,
+    make_token,
+)
+
+# The meta-state DAO through the SAME core copy the app uses
+# (nestquest_core.*, NOT the conftest-stubbed custom_components copy) —
+# used for the tests' database assertions only; the routes reach it
+# through api.nestquest_core.
+_dao_meta = importlib.import_module("nestquest_core.dao_meta")
+
+#: The well-known ``nestquest_meta_state`` key the API stores its
+#: settings under — asserted literally so the contract is pinned here,
+#: independent of the core constant.
+SETTINGS_META_KEY = "settings"
+
+#: The all-defaults effective settings a fresh database reports — the
+#: documented ten fields, asserted literally so the payload contract is
+#: pinned here, independent of the core constants.
+DEFAULT_SETTINGS = {
+    "horizon_days": 14,
+    "day_rollover_time": "00:00",
+    "notify_target": "",
+    "morning_summary_time": "08:00",
+    "afternoon_reminder_time": "15:00",
+    "end_of_day_report_time": "20:00",
+    "morning_summary_enabled": True,
+    "afternoon_reminder_enabled": True,
+    "end_of_day_report_enabled": True,
+    "celebration_enabled": True,
+}
+
+
+def _admin_headers() -> dict[str, str]:
+    """The Authorization header of a valid nestquest-admins JWT."""
+    return {"Authorization": f"Bearer {make_token()}"}
+
+
+@pytest.fixture
+async def settings_client(temp_db_path: str) -> SimpleNamespace:
+    """An admin-plane app client plus its live database.
+
+    The same runner the children tests use (stubbed JWKS, no network);
+    the fixture also exposes the app's ONE database connection so tests
+    can read (or corrupt) the stored settings document itself.
+    """
+    runner = AdminRunner(temp_db_path, jwks_for(ADMIN_KEY, KID))
+    async with runner as client:
+        yield SimpleNamespace(
+            client=client,
+            database=runner.app.state.db.database,
+        )
+
+
+# --- read: the effective settings, defaults on a fresh database --------
+
+
+async def test_get_settings_returns_defaults_on_a_fresh_database(
+    settings_client: SimpleNamespace,
+) -> None:
+    """GET returns the ten documented fields at their defaults."""
+    response = await settings_client.client.get(
+        "/api/v1/admin/settings", headers=_admin_headers()
+    )
+    assert response.status_code == 200
+    assert response.json() == DEFAULT_SETTINGS
+
+
+# --- update: persists, and the NEXT read reflects it --------------------
+
+
+async def test_update_persists_and_the_next_read_reflects_it(
+    settings_client: SimpleNamespace,
+) -> None:
+    """PATCH persists the supplied fields; GET reads them back."""
+    client = settings_client.client
+    changes = {
+        "horizon_days": 21,
+        "day_rollover_time": "03:30",
+        "notify_target": "notify.mobile_app_dads_phone",
+        "celebration_enabled": False,
+    }
+    patched = await client.patch(
+        "/api/v1/admin/settings", json=changes, headers=_admin_headers()
+    )
+    assert patched.status_code == 200
+    expected = {**DEFAULT_SETTINGS, **changes}
+    assert patched.json() == expected
+
+    # The NEXT read reflects the persisted settings...
+    reread = await client.get(
+        "/api/v1/admin/settings", headers=_admin_headers()
+    )
+    assert reread.status_code == 200
+    assert reread.json() == expected
+
+    # ...and the DATABASE holds the merged document: the complete ten
+    # fields, keyed by field name, under the well-known meta_state key.
+    raw = await _dao_meta.MetaStateDao(settings_client.database).get(
+        SETTINGS_META_KEY
+    )
+    assert raw is not None
+    assert json.loads(raw) == expected
+
+
+async def test_partial_update_merges_onto_the_current_settings(
+    settings_client: SimpleNamespace,
+) -> None:
+    """A later PATCH changes only its own fields; the rest survive."""
+    client = settings_client.client
+    first = await client.patch(
+        "/api/v1/admin/settings",
+        json={"horizon_days": 7, "notify_target": " notify.x "},
+        headers=_admin_headers(),
+    )
+    assert first.status_code == 200
+    # The notify target went through the core's own normalizer: stripped.
+    assert first.json()["horizon_days"] == 7
+    assert first.json()["notify_target"] == "notify.x"
+
+    second = await client.patch(
+        "/api/v1/admin/settings",
+        json={"morning_summary_time": "07:45"},
+        headers=_admin_headers(),
+    )
+    assert second.status_code == 200
+    assert second.json() == {
+        **DEFAULT_SETTINGS,
+        "horizon_days": 7,
+        "notify_target": "notify.x",
+        "morning_summary_time": "07:45",
+    }
+
+    reread = await client.get(
+        "/api/v1/admin/settings", headers=_admin_headers()
+    )
+    assert reread.json() == second.json()
+
+
+async def test_empty_update_is_a_noop(
+    settings_client: SimpleNamespace,
+) -> None:
+    """PATCHing no fields leaves the effective settings as they are."""
+    client = settings_client.client
+    response = await client.patch(
+        "/api/v1/admin/settings", json={}, headers=_admin_headers()
+    )
+    assert response.status_code == 200
+    assert response.json() == DEFAULT_SETTINGS
+
+
+async def test_null_resets_a_field_to_its_default(
+    settings_client: SimpleNamespace,
+) -> None:
+    """A JSON ``null`` maps to the field's default (None-as-absent)."""
+    client = settings_client.client
+    set_horizon = await client.patch(
+        "/api/v1/admin/settings",
+        json={"horizon_days": 7},
+        headers=_admin_headers(),
+    )
+    assert set_horizon.status_code == 200
+    assert set_horizon.json()["horizon_days"] == 7
+
+    reset = await client.patch(
+        "/api/v1/admin/settings",
+        json={"horizon_days": None},
+        headers=_admin_headers(),
+    )
+    assert reset.status_code == 200
+    assert reset.json()["horizon_days"] == 14
+
+    reread = await client.get(
+        "/api/v1/admin/settings", headers=_admin_headers()
+    )
+    assert reread.json()["horizon_days"] == 14
+
+
+# --- validation: rejected values never change the stored settings -------
+
+
+@pytest.mark.parametrize(
+    ("changes", "field"),
+    [
+        ({"horizon_days": 0}, "horizon_days"),
+        ({"horizon_days": -3}, "horizon_days"),
+        # A bool is rejected — the core's guardrail survives the route.
+        ({"horizon_days": True}, "horizon_days"),
+        ({"horizon_days": "soon"}, "horizon_days"),
+        ({"day_rollover_time": "25:00"}, "day_rollover_time"),
+        ({"day_rollover_time": "7:30"}, "day_rollover_time"),
+        ({"morning_summary_enabled": "yes"}, "morning_summary_enabled"),
+        ({"celebration_enabled": 1}, "celebration_enabled"),
+        ({"notify_target": 5}, "notify_target"),
+    ],
+)
+async def test_invalid_value_is_rejected_and_stored_settings_unchanged(
+    settings_client: SimpleNamespace, changes: dict[str, object], field: str
+) -> None:
+    """A rejected value is 422 naming the field; the next read is same."""
+    client = settings_client.client
+    seeded = await client.patch(
+        "/api/v1/admin/settings",
+        json={
+            "horizon_days": 21,
+            "day_rollover_time": "01:30",
+            "morning_summary_enabled": False,
+        },
+        headers=_admin_headers(),
+    )
+    assert seeded.status_code == 200
+    before = seeded.json()
+
+    response = await client.patch(
+        "/api/v1/admin/settings", json=changes, headers=_admin_headers()
+    )
+    assert response.status_code == 422, changes
+    assert field in str(response.json()["detail"]), changes
+
+    after = await client.get(
+        "/api/v1/admin/settings", headers=_admin_headers()
+    )
+    assert after.status_code == 200
+    assert after.json() == before
+
+
+async def test_unknown_field_is_rejected_and_stored_settings_unchanged(
+    settings_client: SimpleNamespace,
+) -> None:
+    """An unknown field is 422 naming it — alone or beside a valid one."""
+    client = settings_client.client
+    unknown = await client.patch(
+        "/api/v1/admin/settings",
+        json={"bogus_setting": 1},
+        headers=_admin_headers(),
+    )
+    assert unknown.status_code == 422
+    assert "bogus_setting" in str(unknown.json()["detail"])
+
+    mixed = await client.patch(
+        "/api/v1/admin/settings",
+        json={"horizon_days": 7, "bogus_setting": 1},
+        headers=_admin_headers(),
+    )
+    assert mixed.status_code == 422
+    assert "bogus_setting" in str(mixed.json()["detail"])
+
+    # Neither rejection wrote anything, not even the valid sibling.
+    after = await client.get(
+        "/api/v1/admin/settings", headers=_admin_headers()
+    )
+    assert after.json() == DEFAULT_SETTINGS
+
+
+async def test_non_object_body_is_422(
+    settings_client: SimpleNamespace,
+) -> None:
+    """A body that is not a JSON object is FastAPI's 422 (the shape)."""
+    client = settings_client.client
+    for body in ([1, 2], "nope", 5):
+        response = await client.patch(
+            "/api/v1/admin/settings", json=body, headers=_admin_headers()
+        )
+        assert response.status_code == 422, body
+    # A bare JSON null is likewise not an object.
+    response = await client.patch(
+        "/api/v1/admin/settings",
+        content=b"null",
+        headers={**_admin_headers(), "content-type": "application/json"},
+    )
+    assert response.status_code == 422
+
+    after = await client.get(
+        "/api/v1/admin/settings", headers=_admin_headers()
+    )
+    assert after.json() == DEFAULT_SETTINGS
+
+
+# --- resilience: a corrupt stored document does not crash the service ---
+
+
+async def test_corrupt_stored_document_falls_back_to_defaults(
+    settings_client: SimpleNamespace,
+) -> None:
+    """GET degrades gracefully over an unusable settings document."""
+    client = settings_client.client
+    dao = _dao_meta.MetaStateDao(settings_client.database)
+
+    # Not JSON at all: all defaults, no crash.
+    await dao.set(SETTINGS_META_KEY, "{not-json")
+    response = await client.get(
+        "/api/v1/admin/settings", headers=_admin_headers()
+    )
+    assert response.status_code == 200
+    assert response.json() == DEFAULT_SETTINGS
+
+    # JSON but not an object: all defaults, no crash.
+    await dao.set(SETTINGS_META_KEY, json.dumps([1, 2]))
+    response = await client.get(
+        "/api/v1/admin/settings", headers=_admin_headers()
+    )
+    assert response.status_code == 200
+    assert response.json() == DEFAULT_SETTINGS
+
+    # An object with one invalid field: PER-FIELD fallback — the valid
+    # sibling survives, the invalid one falls back to its default.
+    await dao.set(
+        SETTINGS_META_KEY,
+        json.dumps({"horizon_days": 7, "day_rollover_time": "soon"}),
+    )
+    response = await client.get(
+        "/api/v1/admin/settings", headers=_admin_headers()
+    )
+    assert response.status_code == 200
+    assert response.json() == {**DEFAULT_SETTINGS, "horizon_days": 7}
+
+
+# --- authentication: the ONE require_admin dependency guards both routes
+
+
+async def test_settings_routes_refuse_non_admin_and_absent_credentials(
+    settings_client: SimpleNamespace,
+) -> None:
+    """A non-admin JWT is 403, an absent credential is 401; none write."""
+    client = settings_client.client
+    non_admin = make_token(groups=("some-other-group",))
+    forbidden_get = await client.get(
+        "/api/v1/admin/settings",
+        headers={"Authorization": f"Bearer {non_admin}"},
+    )
+    assert forbidden_get.status_code == 403
+    assert forbidden_get.json()["detail"] == (
+        "Admin access requires membership in the nestquest-admins group"
+    )
+    forbidden_patch = await client.patch(
+        "/api/v1/admin/settings",
+        json={"horizon_days": 7},
+        headers={"Authorization": f"Bearer {non_admin}"},
+    )
+    assert forbidden_patch.status_code == 403
+
+    absent_get = await client.get("/api/v1/admin/settings")
+    assert absent_get.status_code == 401
+    absent_patch = await client.patch(
+        "/api/v1/admin/settings", json={"horizon_days": 7}
+    )
+    assert absent_patch.status_code == 401
+
+    # No refused request changed anything: the settings are untouched.
+    after = await client.get(
+        "/api/v1/admin/settings", headers=_admin_headers()
+    )
+    assert after.json() == DEFAULT_SETTINGS