fix(core): adaptive_threshold input validation + boundary tests

Risponde alla code review di 7dc2fda:
- Valida percentile in [0,1] e 0 < min_days < target_days, raise
  ValueError quando out-of-range. Fail-fast invece di IndexError o
  silent wrong result.
- Aggiunge test boundary esattamente a min_days*96 e target_days*96
  (spec §9.1 item 9 era mancante).
- Aggiunge 4 test sulle nuove guards.
- Fix typo docstring (Determinismic → Deterministic).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/cerbero_bite/core/adaptive_threshold.py

@@ -2,7 +2,7 @@
 
 Spec: ``docs/superpowers/specs/2026-05-08-iv-rv-adaptive-gate-design.md``.
 
-Determinismic, no I/O. La query del repository è effettuata dal caller
+Deterministic, no I/O. La query del repository è effettuata dal caller
 (``runtime/entry_cycle``) prima di chiamare questa funzione.
 """
 
@@ -45,6 +45,15 @@ def compute_adaptive_threshold(
         disabilitato), altrimenti il percentile della finestra,
         bounded dal floor.
     """
+    if not (Decimal(0) <= percentile <= Decimal(1)):
+        raise ValueError(
+            f"percentile must be in [0, 1], got {percentile}"
+        )
+    if min_days <= 0 or target_days <= 0 or min_days >= target_days:
+        raise ValueError(
+            f"require 0 < min_days < target_days, "
+            f"got min_days={min_days}, target_days={target_days}"
+        )
     if not history:
         return None
     n_ticks = len(history)

tests/unit/test_adaptive_threshold.py

@@ -140,3 +140,82 @@ def test_median_percentile_returns_p50() -> None:
     # P50 di [1..200] = (200+1)/2 = 100.5
     assert out is not None
     assert Decimal("100") <= out <= Decimal("101")
+
+
+def test_exactly_min_days_uses_min_window() -> None:
+    """Boundary: history == min_days*96 → window is min_days (per spec 9.1 item 9)."""
+    history = _ramp(30 * 96)  # exactly 2880 ticks
+    out = compute_adaptive_threshold(
+        history=history,
+        percentile=Decimal("0.25"),
+        absolute_floor=Decimal("0"),
+        min_days=30,
+        target_days=60,
+    )
+    # Window = last 2880 = all history; P25 of ramp [1..2880] ≈ 720.75
+    assert out is not None
+    assert Decimal("720") <= out <= Decimal("721")
+
+
+def test_exactly_target_days_uses_target_window() -> None:
+    """Boundary: history == target_days*96 → window is target_days."""
+    history = _ramp(60 * 96)  # exactly 5760 ticks
+    out = compute_adaptive_threshold(
+        history=history,
+        percentile=Decimal("0.25"),
+        absolute_floor=Decimal("0"),
+        min_days=30,
+        target_days=60,
+    )
+    # Window = last 5760 = all history; P25 of ramp [1..5760] ≈ 1440.75
+    assert out is not None
+    assert Decimal("1440") <= out <= Decimal("1441")
+
+
+# ---------------------------------------------------------------------------
+# Input validation
+# ---------------------------------------------------------------------------
+
+
+def test_invalid_percentile_above_one_raises() -> None:
+    with pytest.raises(ValueError, match="percentile must be in"):
+        compute_adaptive_threshold(
+            history=[Decimal("1")] * 200,
+            percentile=Decimal("1.5"),
+            absolute_floor=Decimal("0"),
+            min_days=30,
+            target_days=60,
+        )
+
+
+def test_invalid_percentile_negative_raises() -> None:
+    with pytest.raises(ValueError, match="percentile must be in"):
+        compute_adaptive_threshold(
+            history=[Decimal("1")] * 200,
+            percentile=Decimal("-0.1"),
+            absolute_floor=Decimal("0"),
+            min_days=30,
+            target_days=60,
+        )
+
+
+def test_invalid_window_inverted_raises() -> None:
+    with pytest.raises(ValueError, match="min_days < target_days"):
+        compute_adaptive_threshold(
+            history=[Decimal("1")] * 200,
+            percentile=Decimal("0.25"),
+            absolute_floor=Decimal("0"),
+            min_days=60,
+            target_days=30,
+        )
+
+
+def test_invalid_window_zero_raises() -> None:
+    with pytest.raises(ValueError, match="min_days < target_days"):
+        compute_adaptive_threshold(
+            history=[Decimal("1")] * 200,
+            percentile=Decimal("0.25"),
+            absolute_floor=Decimal("0"),
+            min_days=0,
+            target_days=60,
+        )