diff --git a/gatelock/README.md b/gatelock/README.md
index a79592d..9ef74b1 100644
--- a/gatelock/README.md
+++ b/gatelock/README.md
@@ -72,6 +72,14 @@ leetcode-guard and book-guard all call it; the policy itself stays in
 wake-alarm. Path and retry budget are arguments so each consumer's tests keep
 redirecting their own constant.
 
+`gatelock.night_lockdown.evening_lockdown_today` answers "has tonight's
+evening night-lockdown already happened?" from night-lockdown's
+`/var/lib/night-lockdown/locked_at_epoch` (local date today, local time
+>= 12:00; the 04:01 morning re-lock does not count). Earner gates
+(screen-locker's workout lock, leetcode-guard, book-guard) opt in and do not
+re-arm for the rest of such a day; diet-guard does not. Missing or garbage
+means "no lockdown" (garbage warns), so the gate locks as before.
+
 ## Development
 
 ```bash
diff --git a/gatelock/gatelock/night_lockdown.py b/gatelock/gatelock/night_lockdown.py
new file mode 100644
index 0000000..550731c
--- /dev/null
+++ b/gatelock/gatelock/night_lockdown.py
@@ -0,0 +1,90 @@
+# Copyright (c) 2026 Krzysztof Rudnicki
+"""Has tonight's evening night-lockdown already happened?
+
+night-lockdown (digital-wellbeing, ``night-lockdown-enter.sh``) stamps
+``/var/lib/night-lockdown/locked_at_epoch`` with a unix epoch every time it
+locks, and never removes it. Earner gates (workout, LeetCode, reading) that
+opt in call :func:`evening_lockdown_today` and do not re-arm their lock for
+the rest of a day whose evening lockdown already fired: once a late credit
+lifted that lockdown, re-locking behind a task gate the same evening would
+make the finished task impossible to submit.
+
+Only an EVENING lock counts -- the stamp's local date is today and its local
+time is at or after 12:00. The 04:01 re-lock of the morning window is the
+night that began yesterday, not tonight's.
+
+Fail open to "no lockdown" (the gate locks as before): a missing stamp is the
+normal state on a fresh machine and stays quiet; an unreadable or garbage
+stamp is a warning, because then the signal itself is broken.
+
+Opt-in by design: a gate that is not an earner (diet-guard) never calls this.
+"""
+
+from __future__ import annotations
+
+from datetime import UTC, datetime, time
+import logging
+from pathlib import Path
+from typing import Final
+
+_logger = logging.getLogger(__name__)
+
+NIGHT_LOCKDOWN_STAMP: Final = Path("/var/lib/night-lockdown/locked_at_epoch")
+"""Where night-lockdown-enter.sh writes the epoch of its latest lock."""
+
+EVENING_FROM: Final = time(12, 0)
+"""A same-day lock at or after this local time is the evening lockdown."""
+
+
+def _read_stamp(path: Path) -> datetime | None:
+    """The stamp as a local instant, or None when absent or unusable."""
+    try:
+        text = path.read_text(encoding="ascii")
+    except FileNotFoundError:
+        _logger.debug("No night-lockdown stamp at %s", path)
+        return None
+    except (OSError, UnicodeDecodeError) as exc:
+        _logger.warning(
+            "Cannot read night-lockdown stamp %s (%s); treating as no lockdown",
+            path,
+            exc,
+        )
+        return None
+    try:
+        return datetime.fromtimestamp(int(text.strip()), tz=UTC).astimezone()
+    except (ValueError, OverflowError, OSError) as exc:
+        _logger.warning(
+            "Night-lockdown stamp %s is not a unix epoch (%r: %s); "
+            "treating as no lockdown",
+            path,
+            text[:40],
+            exc,
+        )
+        return None
+
+
+def evening_lockdown_today(
+    path: Path = NIGHT_LOCKDOWN_STAMP,
+    now: datetime | None = None,
+) -> datetime | None:
+    """When today's evening lockdown locked, or None if it has not yet.
+
+    Truthy exactly when the stamp's local date is ``now``'s and its local
+    time is at or after :data:`EVENING_FROM` (and not in the future), so it
+    reads as a predicate while still giving callers the time to quote.
+    """
+    now = (now or datetime.now(tz=UTC)).astimezone()
+    locked_at = _read_stamp(path)
+    if locked_at is None:
+        return None
+    if locked_at.date() != now.date() or locked_at.time() < EVENING_FROM:
+        return None
+    if locked_at > now:
+        _logger.warning(
+            "Night-lockdown stamp %s is in the future (%s > %s); ignoring it",
+            path,
+            locked_at.isoformat(),
+            now.isoformat(),
+        )
+        return None
+    return locked_at
diff --git a/gatelock/gatelock/tests/test_night_lockdown.py b/gatelock/gatelock/tests/test_night_lockdown.py
new file mode 100644
index 0000000..ba6b115
--- /dev/null
+++ b/gatelock/gatelock/tests/test_night_lockdown.py
@@ -0,0 +1,108 @@
+# Copyright (c) 2026 Krzysztof Rudnicki
+"""gatelock.night_lockdown -- has tonight's evening lockdown already happened?"""
+
+from __future__ import annotations
+
+from datetime import UTC, datetime, timedelta
+import logging
+from typing import TYPE_CHECKING
+
+import pytest
+
+from gatelock.night_lockdown import NIGHT_LOCKDOWN_STAMP, evening_lockdown_today
+
+if TYPE_CHECKING:
+    from pathlib import Path
+
+NOW = datetime(2026, 10, 17, 22, 30).astimezone()
+
+
+@pytest.fixture
+def stamp(tmp_path: Path) -> Path:
+    """Where the tests write the stamp -- never the real root-owned one."""
+    return tmp_path / "locked_at_epoch"
+
+
+def _write_local(stamp: Path, when: str) -> None:
+    """Stamp the epoch of a LOCAL wall-clock time, as night-lockdown does."""
+    epoch = int(datetime.fromisoformat(when).astimezone().timestamp())
+    stamp.write_text(f"{epoch}\n")
+
+
+def test_default_path_is_the_one_night_lockdown_writes() -> None:
+    assert str(NIGHT_LOCKDOWN_STAMP) == "/var/lib/night-lockdown/locked_at_epoch"
+
+
+def test_evening_lock_today_counts(stamp: Path) -> None:
+    _write_local(stamp, "2026-10-17T18:00")
+    got = evening_lockdown_today(stamp, NOW)
+    assert got == datetime(2026, 10, 17, 18, 0).astimezone()
+
+
+def test_morning_relock_today_does_not_count(
+    stamp: Path, caplog: pytest.LogCaptureFixture
+) -> None:
+    # The 04:01 re-lock is the night that started yesterday, not tonight's.
+    _write_local(stamp, "2026-10-17T04:01")
+    with caplog.at_level(logging.DEBUG, logger="gatelock.night_lockdown"):
+        assert evening_lockdown_today(stamp, NOW) is None
+    assert not [r for r in caplog.records if r.levelno >= logging.WARNING]
+
+
+def test_noon_is_the_first_evening_minute(stamp: Path) -> None:
+    _write_local(stamp, "2026-10-17T12:00")
+    assert evening_lockdown_today(stamp, NOW) is not None
+
+
+def test_just_before_noon_is_still_morning(stamp: Path) -> None:
+    _write_local(stamp, "2026-10-17T11:59:59")
+    assert evening_lockdown_today(stamp, NOW) is None
+
+
+def test_yesterdays_evening_lock_does_not_count(stamp: Path) -> None:
+    _write_local(stamp, "2026-10-16T21:00")
+    assert evening_lockdown_today(stamp, NOW) is None
+
+
+def test_lock_later_than_now_does_not_count(stamp: Path) -> None:
+    # Clock trouble: a stamp from the future is not a lockdown that happened.
+    _write_local(stamp, "2026-10-17T23:00")
+    assert evening_lockdown_today(stamp, NOW) is None
+
+
+def test_missing_file_is_quiet(stamp: Path, caplog: pytest.LogCaptureFixture) -> None:
+    with caplog.at_level(logging.DEBUG, logger="gatelock.night_lockdown"):
+        assert evening_lockdown_today(stamp, NOW) is None
+    assert not [r for r in caplog.records if r.levelno >= logging.WARNING]
+
+
+@pytest.mark.parametrize("content", ["garbage", "", "  \n", "12.5", "1e9"])
+def test_garbage_warns(
+    stamp: Path, caplog: pytest.LogCaptureFixture, content: str
+) -> None:
+    stamp.write_text(content)
+    with caplog.at_level(logging.WARNING, logger="gatelock.night_lockdown"):
+        assert evening_lockdown_today(stamp, NOW) is None
+    assert any(r.levelno == logging.WARNING for r in caplog.records)
+
+
+def test_absurd_epoch_warns(stamp: Path, caplog: pytest.LogCaptureFixture) -> None:
+    stamp.write_text("9" * 30)
+    with caplog.at_level(logging.WARNING, logger="gatelock.night_lockdown"):
+        assert evening_lockdown_today(stamp, NOW) is None
+    assert any(r.levelno == logging.WARNING for r in caplog.records)
+
+
+def test_unreadable_warns(stamp: Path, caplog: pytest.LogCaptureFixture) -> None:
+    stamp.mkdir()  # reading a directory is an OSError that is not "missing"
+    with caplog.at_level(logging.WARNING, logger="gatelock.night_lockdown"):
+        assert evening_lockdown_today(stamp, NOW) is None
+    assert any(r.levelno == logging.WARNING for r in caplog.records)
+
+
+def test_now_defaults_to_the_local_clock(stamp: Path) -> None:
+    # A stamp a minute ago counts exactly when "a minute ago" is today, >=12:00.
+    ago = datetime.now(tz=UTC).astimezone() - timedelta(minutes=1)
+    stamp.write_text(str(int(ago.timestamp())))
+    expected = ago.date() == (ago + timedelta(minutes=1)).date() and ago.hour >= 12
+    assert (evening_lockdown_today(stamp) is not None) is expected
diff --git a/gatelock/pyproject.toml b/gatelock/pyproject.toml
index 6946c0e..5b9187e 100644
--- a/gatelock/pyproject.toml
+++ b/gatelock/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "gatelock"
-version = "0.9.0"
+version = "0.10.0"
 description = "Shared per-output lock-window + HMAC log-integrity backend for blocking-overlay apps"
 requires-python = ">=3.14"
 dependencies = []  # pure stdlib — tkinter is bundled with Python