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_validator.py

@@ -8,6 +8,7 @@ in its reason, and NO percentiles — so it can never be consumed as validated.
 from __future__ import annotations
 
 import pytest
+from pydantic import ValidationError
 
 from portfolio_optimiser_claude.ir import SavingsProposal
 from portfolio_optimiser_claude.validator import (
@@ -63,3 +64,19 @@ class TestRejectionIsUnconsumable:
         assert isinstance(outcome, Rejection)
         for field in ("p10", "p50", "p90", "validates"):
             assert not hasattr(outcome, field)
+
+
+class TestValidatorCannotBeVacuouslyCleared:
+    """R-2: the review's run proof — ``unit_cost: Infinity`` used to reach the
+    validator and clear it with ``ValidatedProposal(validates=True, p90=inf)``.
+    The IR schema now refuses non-finite numbers, so no proposal the validator
+    can receive carries them (§3 Step 4 stays blocking, never vacuous)."""
+
+    def test_r2_infinity_proposal_cannot_exist(self) -> None:
+        with pytest.raises(ValidationError):
+            SavingsProposal(
+                project_id="P1",
+                measure="m",
+                affected_items=[{"code": "EL", "quantity": 1.0, "unit_cost": float("inf")}],
+                claimed_saving_nok=1e12,
+            )