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/step871_test.cpp

@@ -0,0 +1,51 @@
+// Step 871: Compute/runtime cost estimator from prior runs (10 tests)
+#include "graduation/ComputeCostEstimator.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(no_history_no_data);
+    auto e=ComputeCostEstimator::estimate("py->cpp",{});
+    C(!e.hasHistory,"no history");P();}
+void t2(){T(with_history_has_data);
+    auto e=ComputeCostEstimator::estimate("py->cpp",{{"py->cpp",100,500}});
+    C(e.hasHistory,"history");P();}
+void t3(){T(pair_id_set);
+    auto e=ComputeCostEstimator::estimate("rust->go",{});
+    C(e.pairId=="rust->go","pairId");P();}
+void t4(){T(sample_count_correct);
+    std::vector<PriorRunRecord> h={{"py->cpp",100,500},{"py->cpp",200,600}};
+    auto e=ComputeCostEstimator::estimate("py->cpp",h);
+    C(e.sampleCount==2,"count");P();}
+void t5(){T(average_duration);
+    std::vector<PriorRunRecord> h={{"py->cpp",100,500},{"py->cpp",200,600}};
+    auto e=ComputeCostEstimator::estimate("py->cpp",h);
+    C(e.estimatedDurationMs==150.0f,"avg");P();}
+void t6(){T(average_tokens);
+    std::vector<PriorRunRecord> h={{"py->cpp",100,500},{"py->cpp",200,600}};
+    auto e=ComputeCostEstimator::estimate("py->cpp",h);
+    C(e.estimatedTokens==550.0f,"tokens");P();}
+void t7(){T(single_run);
+    auto e=ComputeCostEstimator::estimate("py->cpp",{{"py->cpp",300,900}});
+    C(e.estimatedDurationMs==300.0f,"single");P();}
+void t8(){T(zero_history_zero_estimate);
+    auto e=ComputeCostEstimator::estimate("py->cpp",{});
+    C(e.estimatedDurationMs==0.0f,"zero");P();}
+void t9(){T(to_json_has_history);
+    auto e=ComputeCostEstimator::estimate("py->cpp",{{"py->cpp",100,500}});
+    auto j=ComputeCostEstimator::toJson(e);
+    C(j.contains("has_history"),"json");P();}
+void t10(){T(to_json_has_sample_count);
+    auto e=ComputeCostEstimator::estimate("py->cpp",{{"py->cpp",100,500}});
+    auto j=ComputeCostEstimator::toJson(e);
+    C(j.contains("sample_count"),"count");P();}
+
+int main(){
+    std::cout<<"Step 871: Compute cost estimator\n";
+    t1();t2();t3();t4();t5();t6();t7();t8();t9();t10();
+    std::cout<<"\nResults: "<<p<<"/"<<(p+f)<<" passed\n";
+    return f?1:0;
+}