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/step876_test.cpp

@@ -0,0 +1,64 @@
+// Step 876: whetstone_estimate_porting_cost MCP tool (8 tests)
+#include "MCPServer.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(tool_registered);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/list"},{"params",{}}});
+    bool found=false;
+    for(auto& t:r["result"]["tools"]) if(t["name"]=="whetstone_estimate_porting_cost") found=true;
+    C(found,"tool found");P();}
+
+void t2(){T(no_pair_id_fails);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/call"},{"params",{{"name","whetstone_estimate_porting_cost"},{"arguments",nlohmann::json::object()}}}});
+    auto res=nlohmann::json::parse(r["result"]["content"][0]["text"].get<std::string>());
+    C(!res["success"].get<bool>(),"fail");P();}
+
+void t3(){T(valid_pair_succeeds);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/call"},{"params",{{"name","whetstone_estimate_porting_cost"},{"arguments",{{"pair_id","py->cpp"}}}}}});
+    auto res=nlohmann::json::parse(r["result"]["content"][0]["text"].get<std::string>());
+    C(res["success"].get<bool>(),"success");P();}
+
+void t4(){T(tier_field_present);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/call"},{"params",{{"name","whetstone_estimate_porting_cost"},{"arguments",{{"pair_id","py->cpp"}}}}}});
+    auto res=nlohmann::json::parse(r["result"]["content"][0]["text"].get<std::string>());
+    C(res.contains("tier"),"tier");P();}
+
+void t5(){T(total_cost_present);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/call"},{"params",{{"name","whetstone_estimate_porting_cost"},{"arguments",{{"pair_id","py->cpp"}}}}}});
+    auto res=nlohmann::json::parse(r["result"]["content"][0]["text"].get<std::string>());
+    C(res.contains("total_cost"),"total");P();}
+
+void t6(){T(high_loc_high_compute);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/call"},{"params",{{"name","whetstone_estimate_porting_cost"},{"arguments",{{"pair_id","py->cpp"},{"lines_of_code",5000},{"ambiguity_score",0.9}}}}}});
+    auto res=nlohmann::json::parse(r["result"]["content"][0]["text"].get<std::string>());
+    C(res["tier"]=="high","high");P();}
+
+void t7(){T(low_loc_low_tier);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/call"},{"params",{{"name","whetstone_estimate_porting_cost"},{"arguments",{{"pair_id","py->cpp"},{"lines_of_code",10},{"ambiguity_score",0.0}}}}}});
+    auto res=nlohmann::json::parse(r["result"]["content"][0]["text"].get<std::string>());
+    C(res["tier"]=="low","low");P();}
+
+void t8(){T(pair_id_in_response);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/call"},{"params",{{"name","whetstone_estimate_porting_cost"},{"arguments",{{"pair_id","rust->go"}}}}}});
+    auto res=nlohmann::json::parse(r["result"]["content"][0]["text"].get<std::string>());
+    C(res["pair_id"]=="rust->go","pair_id");P();}
+
+int main(){
+    std::cout<<"Step 876: whetstone_estimate_porting_cost\n";
+    t1();t2();t3();t4();t5();t6();t7();t8();
+    std::cout<<"\nResults: "<<p<<"/"<<(p+f)<<" passed\n";
+    return f?1:0;
+}