diff --git a/loopx/capabilities/explore/adaptive_replay_planner.py b/loopx/capabilities/explore/adaptive_replay_planner.py
index cefa76463c..6fdbd7914a 100644
--- a/loopx/capabilities/explore/adaptive_replay_planner.py
+++ b/loopx/capabilities/explore/adaptive_replay_planner.py
@@ -10,16 +10,24 @@
 from .trace_runtime import TraceLog, require_nonempty_text
 
 
-def _nonnegative(value: float, field_name: str) -> float:
+def _finite(
+    value: float, field_name: str, requirement: str = "finite number"
+) -> float:
+    message = f"{field_name} must be a {requirement}"
     if isinstance(value, bool):
-        raise ValueError(f"{field_name} must be a finite non-negative number")
+        raise ValueError(message)
     try:
         normalized = float(value)
     except (OverflowError, TypeError, ValueError) as exc:
-        raise ValueError(
-            f"{field_name} must be a finite non-negative number"
-        ) from exc
-    if not math.isfinite(normalized) or normalized < 0:
+        raise ValueError(message) from exc
+    if not math.isfinite(normalized):
+        raise ValueError(message)
+    return normalized
+
+
+def _nonnegative(value: float, field_name: str) -> float:
+    normalized = _finite(value, field_name, "finite non-negative number")
+    if normalized < 0:
         raise ValueError(f"{field_name} must be a finite non-negative number")
     return normalized
 
@@ -94,9 +102,9 @@ def __post_init__(self) -> None:
         )
         if self.minimum_fidelity == ReplayFidelity.NON_REPLAYABLE:
             raise ValueError("failure observations require replayable fidelity")
-        normalized_weight = float(self.weight)
+        normalized_weight = _finite(self.weight, "weight", "finite positive number")
         if normalized_weight <= 0:
-            raise ValueError("weight must be positive")
+            raise ValueError("weight must be a finite positive number")
         object.__setattr__(self, "weight", normalized_weight)
 
 
@@ -169,7 +177,7 @@ def plan_adaptive_replay_points(
         raise TypeError("observations must contain FailureReplayObservation values")
     if int(max_proposals) <= 0:
         raise ValueError("max_proposals must be positive")
-    threshold = float(minimum_score_minutes)
+    threshold = _finite(minimum_score_minutes, "minimum_score_minutes")
     for candidate in normalized_candidates:
         _validate_position(trace, candidate)
     for observation in normalized_observations:
@@ -202,6 +210,9 @@ def plan_adaptive_replay_points(
             )
         if eligible_weight == 0:
             continue
+        _finite(eligible_weight, "eligible_observation_weight")
+        _finite(expected_saved, "expected_saved_minutes")
+        _finite(weighted_suffix_events, "weighted_suffix_events")
         score = expected_saved - candidate.capture_minutes
         if score < threshold:
             continue
diff --git a/tests/test_explore_replay_runtime.py b/tests/test_explore_replay_runtime.py
index d579f489e9..22ee1a67b2 100644
--- a/tests/test_explore_replay_runtime.py
+++ b/tests/test_explore_replay_runtime.py
@@ -1467,6 +1467,74 @@ def test_replay_cost_rejects_non_finite_or_non_numeric_minutes(invalid_minutes)
         )
 
 
+@pytest.mark.parametrize(
+    "invalid_weight",
+    [True, False, float("nan"), float("inf"), float("-inf"), 10**400, None, "invalid", 0, -1],
+)
+def test_adaptive_planner_rejects_invalid_observation_weights(invalid_weight) -> None:
+    with pytest.raises(ValueError, match="weight must be a finite positive number"):
+        FailureReplayObservation(
+            3, 10, 10.0, ReplayFidelity.EXACT, weight=invalid_weight
+        )
+
+
+@pytest.mark.parametrize(
+    "invalid_threshold",
+    [True, False, float("nan"), float("inf"), float("-inf"), 10**400, None, "invalid"],
+)
+def test_adaptive_planner_rejects_invalid_score_thresholds(invalid_threshold) -> None:
+    with pytest.raises(ValueError, match="minimum_score_minutes must be a finite number"):
+        plan_adaptive_replay_points(
+            _planning_trace(),
+            (ReplayPositionCost("planning-event-1", 2, ReplayFidelity.EXACT, 0.0, 0.0),),
+            (FailureReplayObservation(3, 10, 10.0, ReplayFidelity.EXACT),),
+            minimum_score_minutes=invalid_threshold,
+        )
+
+
+@pytest.mark.parametrize(
+    ("weight", "replay_minutes", "repeats", "overflow_field"),
+    [
+        (1e308, 0.0, 2, "eligible_observation_weight"),
+        (10.0, 1e308, 1, "expected_saved_minutes"),
+        (1e308, 0.0, 1, "weighted_suffix_events"),
+    ],
+)
+def test_adaptive_planner_rejects_overflowed_aggregates(
+    weight, replay_minutes, repeats, overflow_field
+) -> None:
+    observation = FailureReplayObservation(
+        3, 10, replay_minutes, ReplayFidelity.EXACT, weight=weight
+    )
+    with pytest.raises(ValueError, match=f"{overflow_field} must be a finite number"):
+        plan_adaptive_replay_points(
+            _planning_trace(),
+            (ReplayPositionCost("planning-event-1", 2, ReplayFidelity.EXACT, 0.0, 0.0),),
+            (observation,) * repeats,
+        )
+
+
+def test_adaptive_planner_preserves_finite_weights_and_negative_thresholds() -> None:
+    import json
+
+    observation = FailureReplayObservation(
+        3, 10, 10.0, ReplayFidelity.EXACT, weight=0.5
+    )
+    candidate = ReplayPositionCost(
+        "planning-event-1", 2, ReplayFidelity.EXACT, 2.0, 0.0
+    )
+    proposals = plan_adaptive_replay_points(
+        _planning_trace(), (candidate,), (observation,), minimum_score_minutes=-1.0
+    )
+
+    assert len(proposals) == 1
+    assert proposals[0].score_minutes == -1.0
+    assert proposals[0].expected_saved_minutes == 1.0
+    assert proposals[0].expected_suffix_events == 8.0
+    assert proposals[0].eligible_observation_weight == 0.5
+    json.dumps(proposals[0].to_record(), allow_nan=False)
+
+
 def test_full_scope_composes_adaptive_children_risk_and_promotion() -> None:
     trace = TraceLog("trace-full-scope", "branch-main")
     prefix = TraceEvent(