diff --git a/src/aelfrice/scoring.py b/src/aelfrice/scoring.py
index 0dbc9a942..12719736f 100644
--- a/src/aelfrice/scoring.py
+++ b/src/aelfrice/scoring.py
@@ -2,9 +2,9 @@
 
 Half-lives (in hours, converted to seconds below):
     factual     336   (14 days)
+    requirement 720   (30 days)
     preference  2016  (12 weeks)
     correction  4032  (24 weeks)
-    requirement 4032  (24 weeks)
 
 Lock-floor: when a belief's lock_level is "user", decay() is a no-op
 regardless of age (zero work, sharp step). Above the floor decay is
@@ -20,9 +20,9 @@
 _HOUR: Final[float] = 3600.0
 TYPE_HALF_LIFE_SECONDS: Final[dict[str, float]] = {
     "factual": 336.0 * _HOUR,         # 14 days
+    "requirement": 720.0 * _HOUR,     # 30 days
     "preference": 2016.0 * _HOUR,     # 12 weeks
     "correction": 4032.0 * _HOUR,     # 24 weeks
-    "requirement": 4032.0 * _HOUR,    # 24 weeks
 }
 
 # Jeffreys prior -- decay target.
diff --git a/tests/test_type_half_lives.py b/tests/test_type_half_lives.py
new file mode 100644
index 000000000..d08308176
--- /dev/null
+++ b/tests/test_type_half_lives.py
@@ -0,0 +1,53 @@
+"""Type-specific half-lives match the spec exactly.
+
+Spec (carried from the previous codebase's CHANGELOG and confirmed by R&D):
+    factual     336h   (14 days)
+    requirement 720h   (30 days)
+    preference  2016h  (12 weeks)
+    correction  4032h  (24 weeks)
+
+If any of these values drifts, decay behavior in production silently changes
+and downstream property tests (test_decay_required, test_lock_floor_sharp)
+no longer assert what they appear to assert. Lock the values in here.
+"""
+from __future__ import annotations
+
+from aelfrice.scoring import TYPE_HALF_LIFE_SECONDS, type_half_life
+
+_HOUR_SECONDS = 3600.0
+
+
+def test_factual_half_life_336_hours() -> None:
+    assert TYPE_HALF_LIFE_SECONDS["factual"] == 336.0 * _HOUR_SECONDS
+
+
+def test_requirement_half_life_720_hours() -> None:
+    assert TYPE_HALF_LIFE_SECONDS["requirement"] == 720.0 * _HOUR_SECONDS
+
+
+def test_preference_half_life_2016_hours() -> None:
+    assert TYPE_HALF_LIFE_SECONDS["preference"] == 2016.0 * _HOUR_SECONDS
+
+
+def test_correction_half_life_4032_hours() -> None:
+    assert TYPE_HALF_LIFE_SECONDS["correction"] == 4032.0 * _HOUR_SECONDS
+
+
+def test_only_four_belief_types_have_half_lives() -> None:
+    """No drift via accidental extra entries."""
+    assert set(TYPE_HALF_LIFE_SECONDS.keys()) == {
+        "factual",
+        "requirement",
+        "preference",
+        "correction",
+    }
+
+
+def test_type_half_life_lookup_returns_factual_for_unknown_type() -> None:
+    """Unknown types fall back to factual (most aggressive decay)."""
+    assert type_half_life("nonexistent") == TYPE_HALF_LIFE_SECONDS["factual"]
+
+
+def test_type_half_life_lookup_returns_each_known_value() -> None:
+    for t, hl in TYPE_HALF_LIFE_SECONDS.items():
+        assert type_half_life(t) == hl