feat(harness): add information gain stop and audit

src/main/java/com/superbiz/agent/harness/progress/DiagnosisProgressSnapshot.java

@@ -0,0 +1,26 @@
+package com.superbiz.agent.harness.progress;
+
+import com.superbiz.agent.harness.contract.SafeFallback;
+
+import java.util.List;
+
+public record DiagnosisProgressSnapshot(
+        List<SafeFallback.VerifiedSource> verifiedSources,
+        List<SafeFallback.ObservedFact> observedFacts,
+        List<String> limitations,
+        DiagnosisStopReason stopReason) {
+
+    public DiagnosisProgressSnapshot {
+        verifiedSources = verifiedSources == null ? List.of() : List.copyOf(verifiedSources);
+        observedFacts = observedFacts == null ? List.of() : List.copyOf(observedFacts);
+        limitations = limitations == null ? List.of() : List.copyOf(limitations);
+    }
+
+    public static DiagnosisProgressSnapshot empty() {
+        return new DiagnosisProgressSnapshot(List.of(), List.of(), List.of(), null);
+    }
+
+    public boolean hasObservedFacts() {
+        return !observedFacts.isEmpty();
+    }
+}