feat: self-improving skills loop — observe, inspect, amend, evaluate

- Add skill health observation layer (execution logging, success/failure tracking)
- Add skill health inspector (trace recurring failures across runs)
- Add amendify mechanism (propose SKILL.md patches from failure evidence)
- Add evaluation scaffolding (compare amended vs original performance)
- Wire into session-inspect CLI: skills:health, skills:amendify, skills:evaluate
- 1145/1145 tests passing (+3 new)

scripts/lib/skill-improvement/evaluate.js

@@ -0,0 +1,59 @@
+'use strict';
+
+const EVALUATION_SCHEMA_VERSION = 'ecc.skill-evaluation.v1';
+
+function roundRate(value) {
+  return Math.round(value * 1000) / 1000;
+}
+
+function summarize(records) {
+  const runs = records.length;
+  const successes = records.filter(record => record.outcome && record.outcome.success).length;
+  const failures = runs - successes;
+  return {
+    runs,
+    successes,
+    failures,
+    successRate: runs > 0 ? roundRate(successes / runs) : 0
+  };
+}
+
+function buildSkillEvaluationScaffold(skillId, records, options = {}) {
+  const minimumRunsPerVariant = options.minimumRunsPerVariant || 2;
+  const amendmentId = options.amendmentId || null;
+  const filtered = records.filter(record => record.skill && record.skill.id === skillId);
+  const baseline = filtered.filter(record => !record.run || record.run.variant !== 'amended');
+  const amended = filtered.filter(record => record.run && record.run.variant === 'amended')
+    .filter(record => !amendmentId || record.run.amendmentId === amendmentId);
+
+  const baselineSummary = summarize(baseline);
+  const amendedSummary = summarize(amended);
+  const delta = {
+    successRate: roundRate(amendedSummary.successRate - baselineSummary.successRate),
+    failures: amendedSummary.failures - baselineSummary.failures
+  };
+
+  let recommendation = 'insufficient-data';
+  if (baselineSummary.runs >= minimumRunsPerVariant && amendedSummary.runs >= minimumRunsPerVariant) {
+    recommendation = delta.successRate > 0 ? 'promote-amendment' : 'keep-baseline';
+  }
+
+  return {
+    schemaVersion: EVALUATION_SCHEMA_VERSION,
+    generatedAt: new Date().toISOString(),
+    skillId,
+    amendmentId,
+    gate: {
+      minimumRunsPerVariant
+    },
+    baseline: baselineSummary,
+    amended: amendedSummary,
+    delta,
+    recommendation
+  };
+}
+
+module.exports = {
+  EVALUATION_SCHEMA_VERSION,
+  buildSkillEvaluationScaffold
+};