feat(validator): S6 — deterministic backbone: typed IR, golden-frozen validator, provenance stamp

TDD from method-spec alone (§3 Step 4, §7, §9), golden.json as the only
ground truth: ir.py (construction invariants, fail-fast bundle loader),
validator.py (closed-form feasibility bound 0.30·Σ + Monte Carlo seed
20260624/512 samples/inclusive quantiles — reproduces every frozen golden
field; Rejection as a distinct unconsumable type), provenance.py (stamp
mirroring ONLY the deterministic validator). Mutation controls + seed-detach
proof (§11); 45/45 green without an API key; ruff + mypy --strict clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QdSfQdND84oeq2mbjueLTS

tests/test_ir.py

@@ -0,0 +1,86 @@
+"""Typed cost-IR tests (method-spec §7.1).
+
+Schema invariants are enforced at IR construction, so a malformed proposal can never
+exist as a value (§3 Step 2). Loading the IR projection from a bundle is FAIL-FAST:
+a missing file raises (required input — contrast the tolerant inbox, §5). Pure
+config/file-layer — no model client, no API key, no network.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Any
+
+import pytest
+from pydantic import ValidationError
+
+from portfolio_optimiser_claude.ir import SavingsProposal, load_validator_input
+
+BUNDLE = Path(__file__).resolve().parents[1] / "shared" / "examples" / "bygg-energi-mikro"
+
+VALID: dict[str, Any] = {
+    "project_id": "P1",
+    "measure": "LED retrofit",
+    "affected_items": [{"code": "EL", "quantity": 1000, "unit_cost": 1.0}],
+    "claimed_saving_nok": 200,
+    "assumptions": {"EL": [0.8, 1.2]},
+}
+
+
+def build(**overrides: Any) -> SavingsProposal:
+    return SavingsProposal(**{**VALID, **overrides})
+
+
+class TestSchemaInvariants:
+    """§7.1: invariants hold at construction — a schema error, never a validator call."""
+
+    def test_valid_proposal_constructs(self) -> None:
+        proposal = build()
+        assert proposal.project_id == "P1"
+        assert proposal.assumptions["EL"] == (0.8, 1.2)
+
+    def test_empty_affected_items_rejected(self) -> None:
+        with pytest.raises(ValidationError):
+            build(affected_items=[])
+
+    def test_negative_quantity_rejected(self) -> None:
+        with pytest.raises(ValidationError):
+            build(affected_items=[{"code": "EL", "quantity": -1, "unit_cost": 1.0}])
+
+    @pytest.mark.parametrize("bad", [0, -0.5])
+    def test_nonpositive_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", [0, -100])
+    def test_nonpositive_claimed_saving_rejected(self, bad: float) -> None:
+        with pytest.raises(ValidationError):
+            build(claimed_saving_nok=bad)
+
+    def test_claim_above_affected_total_is_schema_error(self) -> None:
+        # The claimed saving MUST NOT exceed the affected items' own total
+        # (Σ quantity·unit_cost = 1000) — a schema error, not a validator rejection.
+        with pytest.raises(ValidationError):
+            build(claimed_saving_nok=1001)
+
+    def test_claim_equal_to_affected_total_allowed(self) -> None:
+        assert build(claimed_saving_nok=1000).claimed_saving_nok == 1000
+
+    def test_assumptions_default_to_empty(self) -> None:
+        # Empty assumptions = degenerate band, no spread (§7.1).
+        proposal = build(assumptions={})
+        assert proposal.assumptions == {}
+
+
+class TestFailFastLoader:
+    """§7.1: the IR projection is required input — a missing file raises."""
+
+    def test_loads_shared_bundle_projection_unchanged(self) -> None:
+        proposal = load_validator_input(BUNDLE)
+        assert proposal.project_id == "BYGG-KONTOR-NORD"
+        assert [item.code for item in proposal.affected_items] == ["ENERGI-TOTAL-EL"]
+        assert proposal.assumptions["ENERGI-TOTAL-EL"] == (0.70, 1.40)
+
+    def test_missing_projection_raises(self, tmp_path: Path) -> None:
+        with pytest.raises(FileNotFoundError):
+            load_validator_input(tmp_path)