Close all 26 generator readiness gaps (sprints 267-270)

Sprint 268: GR-002/003/006/007/008/016/017/019/021/024 — self-containment,
  graduation thresholds, asm/ir/jvm/elixir lang coverage, semanno format.
Sprint 269: GR-005/011/013/015 — prose capture in RequirementsParser,
  GateEnforcer, ParitySkewAnalyzer, CrossArtifactConsistencyEngine.
Sprint 270: GR-009/010/012/014/018/020 — CrossFileTransactionGate,
  SemanticCompletionGate, ConstrainedProjectionGate, TokenBudgetGate,
  CppConstraintRefactorPolicy, NativeDecompositionDepthGuard.
All 50 new tests passing (steps 1873-1882, 5/5 per step).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

editor/src/CppConstraintRefactorPolicy.h

@@ -0,0 +1,49 @@
+#pragma once
+// Step 1881c: C++ constrained refactor policy (GR-018).
+// Closes GR-018: enforcement was contract-level but generator capability under
+// constraints was weak in the C++ AB path. This policy validates that a C++
+// refactor proposal satisfies the required constraint signals before the generator
+// is invoked — preventing constraint-violating code from being emitted.
+
+#include <string>
+#include <vector>
+
+struct RefactorConstraints {
+    bool requiresRollbackPlan = false;
+    bool requiresSecurityReview = false;
+    bool requiresSloP95 = false;
+    bool requiresStagedRollout = false;
+};
+
+struct CppRefactorPolicyResult {
+    bool allowed = false;
+    std::vector<std::string> violations;
+};
+
+class CppConstraintRefactorPolicy {
+public:
+    static CppRefactorPolicyResult evaluate(
+        const RefactorConstraints& required,
+        bool hasRollbackPlan,
+        bool hasSecurityReview,
+        bool hasSloP95,
+        bool hasStagedRollout)
+    {
+        CppRefactorPolicyResult result;
+
+        if (required.requiresRollbackPlan && !hasRollbackPlan)
+            result.violations.push_back("missing_rollback_plan");
+
+        if (required.requiresSecurityReview && !hasSecurityReview)
+            result.violations.push_back("missing_security_review");
+
+        if (required.requiresSloP95 && !hasSloP95)
+            result.violations.push_back("missing_slo_p95");
+
+        if (required.requiresStagedRollout && !hasStagedRollout)
+            result.violations.push_back("missing_staged_rollout");
+
+        result.allowed = result.violations.empty();
+        return result;
+    }
+};