Sprint 63: Learned Adapter Hints (Non-Authoritative) — Steps 859-868

Implements the learned adapter hints layer with governance guardrails:
- HintFeatureExtractor: extract features from decision ledgers (step 859)
- HintModelInterface: pair-specific hint query interface (step 860)
- DeterministicFallback: safe fallback when hints unavailable (step 861)
- HintConfidencePacket: confidence bands and escalation logic (step 862)
- HintABHarness: A/B harness to measure hint effectiveness (step 863)
- HintRollbackControl: suppress and lift hint suppression per pair (step 864)
- whetstone_get_adapter_hints MCP tool (step 865)
- whetstone_set_hint_policy MCP tool (step 866)
- HintSafetyGuardrails: non-authoritative enforcement + audit (step 867)
- Sprint63IntegrationSummary (step 868)

All 10 steps passing (94 tests). Governance rule: learned hints may
suggest; deterministic policy decides.

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

editor/tests/step866_test.cpp

@@ -0,0 +1,64 @@
+// Step 866: whetstone_set_hint_policy 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_set_hint_policy") 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_set_hint_policy"},{"arguments",{{"policy","enabled"}}}}}});
+    auto res=nlohmann::json::parse(r["result"]["content"][0]["text"].get<std::string>());
+    C(!res["success"].get<bool>(),"fail");P();}
+
+void t3(){T(invalid_policy_fails);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/call"},{"params",{{"name","whetstone_set_hint_policy"},{"arguments",{{"pair_id","py->cpp"},{"policy","invalid"}}}}}});
+    auto res=nlohmann::json::parse(r["result"]["content"][0]["text"].get<std::string>());
+    C(!res["success"].get<bool>(),"fail");P();}
+
+void t4(){T(enabled_policy_succeeds);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/call"},{"params",{{"name","whetstone_set_hint_policy"},{"arguments",{{"pair_id","py->cpp"},{"policy","enabled"}}}}}});
+    auto res=nlohmann::json::parse(r["result"]["content"][0]["text"].get<std::string>());
+    C(res["success"].get<bool>(),"success");P();}
+
+void t5(){T(disabled_policy_succeeds);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/call"},{"params",{{"name","whetstone_set_hint_policy"},{"arguments",{{"pair_id","py->cpp"},{"policy","disabled"}}}}}});
+    auto res=nlohmann::json::parse(r["result"]["content"][0]["text"].get<std::string>());
+    C(res["success"].get<bool>(),"success");P();}
+
+void t6(){T(audit_only_policy_succeeds);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/call"},{"params",{{"name","whetstone_set_hint_policy"},{"arguments",{{"pair_id","py->cpp"},{"policy","audit_only"}}}}}});
+    auto res=nlohmann::json::parse(r["result"]["content"][0]["text"].get<std::string>());
+    C(res["success"].get<bool>(),"success");P();}
+
+void t7(){T(response_has_policy);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/call"},{"params",{{"name","whetstone_set_hint_policy"},{"arguments",{{"pair_id","py->cpp"},{"policy","enabled"}}}}}});
+    auto res=nlohmann::json::parse(r["result"]["content"][0]["text"].get<std::string>());
+    C(res["policy"]=="enabled","policy");P();}
+
+void t8(){T(response_has_pair_id);
+    MCPServer srv;
+    auto r=srv.handleRequest({{"jsonrpc","2.0"},{"id",1},{"method","tools/call"},{"params",{{"name","whetstone_set_hint_policy"},{"arguments",{{"pair_id","rust->go"},{"policy","disabled"}}}}}});
+    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 866: whetstone_set_hint_policy\n";
+    t1();t2();t3();t4();t5();t6();t7();t8();
+    std::cout<<"\nResults: "<<p<<"/"<<(p+f)<<" passed\n";
+    return f?1:0;
+}