Sprint 64: Cost-Aware Transpilation Planning — Steps 869-878

Adds cost modeling and budget enforcement for transpilation runs:
- PortingCostModel: LOC + ambiguity → compute/review/total cost + tier (step 869)
- ReviewEffortEstimator: ambiguity/risk → minutes + complexity label (step 870)
- ComputeCostEstimator: prior run history → avg duration/tokens (step 871)
- MultiPlanAlternativeGenerator: cheap/balanced/rigorous profiles (step 872)
- BudgetPolicyEnforcer: approve/requires_token/rejected decisions (step 873)
- CostQualityTradeoffReport: efficiency-based plan recommendation (step 874)
- whetstone_plan_transpilation_run MCP tool (step 875)
- whetstone_estimate_porting_cost MCP tool (step 876)
- CostTelemetryIntegration: cost error tracking + over-budget count (step 877)
- Sprint64IntegrationSummary (step 878)

All 10 steps passing (94 tests). Policy: over-budget plans require
explicit reviewer approval token.

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

editor/tests/step874_test.cpp

@@ -0,0 +1,50 @@
+// Step 874: Cost-vs-quality tradeoff report generator (8 tests)
+#include "graduation/CostQualityTradeoffReport.h"
+#include <iostream>
+static int p=0,f=0;
+#define T(n) { std::cout << "  " << #n << "... "; }
+#define P() { std::cout << "PASS\n"; ++p; }
+#define F(m) { std::cout << "FAIL: " << m << "\n"; ++f; }
+#define C(c,m) if(!(c)){F(m);return;}
+
+void t1(){T(pair_id_set);
+    auto r=CostQualityTradeoffReport::generate("py->cpp",
+        {{"cheap",0.2f},{"rigorous",0.8f}},{{"cheap",0.6f},{"rigorous",0.95f}});
+    C(r.pairId=="py->cpp","pairId");P();}
+void t2(){T(entries_count);
+    auto r=CostQualityTradeoffReport::generate("py->cpp",
+        {{"cheap",0.2f},{"balanced",0.5f}},{{"cheap",0.6f},{"balanced",0.8f}});
+    C(r.entries.size()==2,"size");P();}
+void t3(){T(recommended_profile_set);
+    auto r=CostQualityTradeoffReport::generate("py->cpp",
+        {{"cheap",0.2f},{"balanced",0.5f}},{{"cheap",0.6f},{"balanced",0.8f}});
+    C(!r.recommendedProfile.empty(),"rec");P();}
+void t4(){T(efficiency_computed);
+    auto r=CostQualityTradeoffReport::generate("py->cpp",
+        {{"cheap",0.2f}},{{"cheap",0.6f}});
+    C(r.entries[0].efficiency>0.0f,"eff");P();}
+void t5(){T(best_efficiency_recommended);
+    // cheap: 0.6/0.2 = 3.0, balanced: 0.8/0.5 = 1.6 → cheap wins
+    auto r=CostQualityTradeoffReport::generate("py->cpp",
+        {{"cheap",0.2f},{"balanced",0.5f}},{{"cheap",0.6f},{"balanced",0.8f}});
+    C(r.recommendedProfile=="cheap","cheap");P();}
+void t6(){T(to_json_has_entries);
+    auto r=CostQualityTradeoffReport::generate("py->cpp",
+        {{"cheap",0.2f}},{{"cheap",0.6f}});
+    auto j=CostQualityTradeoffReport::toJson(r);
+    C(j["entries"].is_array(),"entries");P();}
+void t7(){T(to_json_has_recommended);
+    auto r=CostQualityTradeoffReport::generate("py->cpp",
+        {{"cheap",0.2f}},{{"cheap",0.6f}});
+    auto j=CostQualityTradeoffReport::toJson(r);
+    C(j.contains("recommended_profile"),"rec");P();}
+void t8(){T(empty_plans_empty_entries);
+    auto r=CostQualityTradeoffReport::generate("py->cpp",{},{});
+    C(r.entries.empty(),"empty");P();}
+
+int main(){
+    std::cout<<"Step 874: Cost-vs-quality tradeoff report\n";
+    t1();t2();t3();t4();t5();t6();t7();t8();
+    std::cout<<"\nResults: "<<p<<"/"<<(p+f)<<" passed\n";
+    return f?1:0;
+}