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/step867_test.cpp

@@ -0,0 +1,44 @@
+// Step 867: Hint safety guardrails and audit fields (8 tests)
+#include "graduation/HintSafetyGuardrails.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(check_passes_valid);
+    auto r=HintSafetyGuardrails::check("H-1",0.8f,true,true);
+    C(r.passed,"passed");P();}
+void t2(){T(check_fails_authoritative);
+    auto r=HintSafetyGuardrails::check("H-1",0.8f,false,true);
+    C(!r.passed,"failed");P();}
+void t3(){T(check_fails_no_deterministic_policy);
+    auto r=HintSafetyGuardrails::check("H-1",0.8f,true,false);
+    C(!r.passed,"failed");P();}
+void t4(){T(violation_in_list);
+    auto r=HintSafetyGuardrails::check("H-1",0.8f,false,true);
+    C(!r.violations.empty(),"violations");P();}
+void t5(){T(hint_id_set);
+    auto r=HintSafetyGuardrails::check("H-99",0.8f,true,true);
+    C(r.hintId=="H-99","id");P();}
+void t6(){T(audit_record_from_check);
+    auto c=HintSafetyGuardrails::check("H-1",0.8f,true,true);
+    auto a=HintSafetyGuardrails::audit("H-1","py->cpp",c);
+    C(a.guardPassed,"passed");P();}
+void t7(){T(audit_guard_reason_on_fail);
+    auto c=HintSafetyGuardrails::check("H-1",0.8f,false,true);
+    auto a=HintSafetyGuardrails::audit("H-1","py->cpp",c);
+    C(!a.guardReason.empty(),"reason");P();}
+void t8(){T(to_json_has_guard_passed);
+    auto c=HintSafetyGuardrails::check("H-1",0.8f,true,true);
+    auto a=HintSafetyGuardrails::audit("H-1","py->cpp",c);
+    auto j=HintSafetyGuardrails::toJson(a);
+    C(j.contains("guard_passed"),"json");P();}
+
+int main(){
+    std::cout<<"Step 867: Hint safety guardrails\n";
+    t1();t2();t3();t4();t5();t6();t7();t8();
+    std::cout<<"\nResults: "<<p<<"/"<<(p+f)<<" passed\n";
+    return f?1:0;
+}