feat(#85): IMP catalog builder invariant + VP runtime gate (u1~u7)

- u1: BuilderMissingError(FitError) — narrow exception aligned with pipeline catch
- u2: load_frame_contracts catalog invariant + VP skip + CatalogInvariantError
- u3a: audit CLI I1~I3 (partial existence / declared builder / registry membership)
- u3b: audit CLI I4 (slot_payload refs vs declared/generated payload keys)
- u4: lookup_v4_candidates VP filter (lookup_v4_all_judgments raw telemetry untouched)
- u5: catalog invariant regression coverage + temp non-VP failure fixtures
- u6: mdx04 VP routing fixture tests (sw_dependency_four_problems excluded from live)
- u7: tests/conftest.py env isolation + mdx03/mdx04/mdx05 subprocess smoke

Targeted 74 PASS (12.31s). Full regression 1063 PASS (87.70s). Audit CLI clean.

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

src/phase_z2_mapper.py

@@ -42,6 +42,22 @@ class FitError(Exception):
     """
 
 
+class BuilderMissingError(FitError):
+    """Contract.payload.builder ↔ PAYLOAD_BUILDERS registry mismatch.
+
+    FitError subclass — pipeline 의 기존 `except FitError` 경로가 그대로
+    adapter_needed 로 라우팅 (mdx04 hard crash 차단, IMP-#85 u1).
+    """
+
+
+class CatalogInvariantError(Exception):
+    """Catalog ↔ runtime registry drift detected at load time.
+
+    Boot-time invariant violation (IMP-#85 u2). Distinct from FitError:
+    runtime fallback 대상이 아니라 catalog wiring 결함 (fail-fast).
+    """
+
+
 # ─── Catalog loading ──────────────────────────────────────────────
 
 _CATALOG_CACHE: dict | None = None
@@ -50,7 +66,9 @@ _CATALOG_CACHE: dict | None = None
 def load_frame_contracts() -> dict:
     global _CATALOG_CACHE
     if _CATALOG_CACHE is None:
-        _CATALOG_CACHE = yaml.safe_load(CATALOG_PATH.read_text(encoding="utf-8")) or {}
+        catalog = yaml.safe_load(CATALOG_PATH.read_text(encoding="utf-8")) or {}
+        _check_catalog_builder_invariant(catalog)
+        _CATALOG_CACHE = catalog
     return _CATALOG_CACHE
 
 
@@ -686,6 +704,50 @@ PAYLOAD_BUILDERS: dict[str, Callable] = {
 }
 
 
+# ─── Catalog builder invariant (IMP-#85 u2) ──────────────────────
+
+def _check_catalog_builder_invariant(catalog: dict) -> None:
+    """Every non-`visual_pending` contract must declare a registered builder.
+
+    `visual_pending: true` contracts are scaffolding records whose builders
+    are tracked as VP backlog (별 axis IMP-04b / #42) — skipped here so the
+    catalog can keep declaring them without breaking boot.
+
+    Violations are aggregated and raised together so first-fix iteration sees
+    the full drift surface, not just the first row.
+
+    Raises:
+        CatalogInvariantError — when one or more live (non-VP) contracts
+            either omit `payload.builder` or reference a name absent from
+            `PAYLOAD_BUILDERS`.
+    """
+    violations: list[str] = []
+    for template_id, contract in catalog.items():
+        if not isinstance(contract, dict):
+            continue
+        if contract.get("visual_pending") is True:
+            continue
+        payload = contract.get("payload") or {}
+        builder_name = payload.get("builder") if isinstance(payload, dict) else None
+        if not builder_name:
+            violations.append(
+                f"Contract '{template_id}' (non-VP) missing payload.builder."
+            )
+            continue
+        if builder_name not in PAYLOAD_BUILDERS:
+            violations.append(
+                f"Contract '{template_id}' (non-VP) references payload.builder="
+                f"'{builder_name}' not in PAYLOAD_BUILDERS registry."
+            )
+    if violations:
+        raise CatalogInvariantError(
+            f"Catalog builder invariant violated "
+            f"({len(violations)} non-VP contract(s)):\n  - "
+            + "\n  - ".join(violations)
+            + f"\nRegistered builders: {sorted(PAYLOAD_BUILDERS.keys())}"
+        )
+
+
 # ─── Generic mapper (single dispatch via builder) ────────────────
 
 def _check_cardinality(contract: dict, units: list, section) -> None:
@@ -843,13 +905,13 @@ def map_with_contract(section, contract: dict) -> dict:
     payload_spec = contract["payload"]
     builder_name = payload_spec.get("builder")
     if not builder_name:
-        raise ValueError(
+        raise BuilderMissingError(
             f"Contract '{contract['template_id']}' missing payload.builder. "
             f"available: {sorted(PAYLOAD_BUILDERS.keys())}"
         )
     builder = PAYLOAD_BUILDERS.get(builder_name)
     if builder is None:
-        raise ValueError(
+        raise BuilderMissingError(
             f"Contract '{contract['template_id']}' references payload.builder="
             f"'{builder_name}' but PAYLOAD_BUILDERS has no such entry. "
             f"available: {sorted(PAYLOAD_BUILDERS.keys())}"