fix(validator): C2.6 — finiteness hardening, Infinity can no longer vacuously clear the gate (closes R-2)

IR schema now refuses non-finite numbers (allow_inf_nan=False on quantity/
unit_cost/claimed_saving_nok) and non-finite or negative assumption-band
endpoints; json.loads accepts the bare Infinity literal, so the bundle seam
is tested directly. ModelMapContract rejects empty-string model ids
(min_length=1). check_turn_safety_net documented as a deliberately
unreachable belt under the range-bound debate loop.

18 new tests; detach-proven (re-allow inf/nan -> 5 red, drop min_length ->
2 red). Full gate: 365 passed, ruff/format/mypy clean; golden untouched.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_ir.py

@@ -72,6 +72,50 @@ class TestSchemaInvariants:
         assert proposal.assumptions == {}
 
 
+class TestFiniteness:
+    """R-2 hardening: non-finite numbers are schema errors — the mandatory validator
+    can never be vacuously cleared by ``Infinity`` (today's defect: ``validates=True``
+    with ``p90=inf``). Detach point: re-allow inf/nan on any field → these go red."""
+
+    @pytest.mark.parametrize("bad", [float("inf"), float("-inf"), float("nan")])
+    def test_nonfinite_unit_cost_rejected(self, bad: float) -> None:
+        with pytest.raises(ValidationError):
+            build(affected_items=[{"code": "EL", "quantity": 1000, "unit_cost": bad}])
+
+    @pytest.mark.parametrize("bad", [float("inf"), float("nan")])
+    def test_nonfinite_quantity_rejected(self, bad: float) -> None:
+        with pytest.raises(ValidationError):
+            build(affected_items=[{"code": "EL", "quantity": bad, "unit_cost": 1.0}])
+
+    @pytest.mark.parametrize("bad", [float("inf"), float("nan")])
+    def test_nonfinite_claimed_saving_rejected(self, bad: float) -> None:
+        with pytest.raises(ValidationError):
+            build(claimed_saving_nok=bad)
+
+    @pytest.mark.parametrize(
+        "band",
+        [
+            (0.8, float("inf")),
+            (float("-inf"), 1.2),
+            (float("nan"), 1.2),
+            (0.8, float("nan")),
+        ],
+    )
+    def test_nonfinite_assumption_band_endpoint_rejected(self, band: tuple[float, float]) -> None:
+        with pytest.raises(ValidationError):
+            build(assumptions={"EL": band})
+
+    @pytest.mark.parametrize("band", [(-0.1, 1.2), (0.8, -1.2)])
+    def test_negative_assumption_band_endpoint_rejected(self, band: tuple[float, float]) -> None:
+        # A band endpoint is a sampled unit cost — a negative cost is a schema error.
+        with pytest.raises(ValidationError):
+            build(assumptions={"EL": band})
+
+    def test_finite_band_still_constructs(self) -> None:
+        # Regression control: the golden bundle's finite numbers are untouched.
+        assert build(assumptions={"EL": (0.70, 1.40)}).assumptions["EL"] == (0.70, 1.40)
+
+
 class TestFailFastLoader:
     """§7.1: the IR projection is required input — a missing file raises."""
 
@@ -84,3 +128,16 @@ class TestFailFastLoader:
     def test_missing_projection_raises(self, tmp_path: Path) -> None:
         with pytest.raises(FileNotFoundError):
             load_validator_input(tmp_path)
+
+    def test_infinity_in_bundle_projection_rejected(self, tmp_path: Path) -> None:
+        # R-2's actual entry seam: ``json.loads`` accepts the bare ``Infinity``
+        # literal, so a bundle file can carry a non-finite number into the IR —
+        # construction must refuse it before the validator ever sees it.
+        (tmp_path / "validator-input.json").write_text(
+            '{"project_id": "P1", "measure": "m", '
+            '"affected_items": [{"code": "EL", "quantity": 1.0, "unit_cost": Infinity}], '
+            '"claimed_saving_nok": 100}',
+            encoding="utf-8",
+        )
+        with pytest.raises(ValidationError):
+            load_validator_input(tmp_path)