feat(confidence-engine): v0.60g1 list investigation summaries

Recover to clean v0.60f then implement only the storage listing contract.

- Add listInvestigations() to provider: enumerate by prefix, project lightweight summary (id, scenario, updatedAt, investigationRevision, reportExists, reportGeneratedFromRevision), sort by updatedAt desc
- Add application-facing wrapper in investigation-storage.js
- Add 8 deterministic tests covering all listing invariants (coexistence, correct IDs, lightweight projection, legacy exclusion, unrelated exclusion, independent update, ordering, malformed skip)
- Fix MockStorageMap WebStorage API compatibility (.length + .key(i))
- Portfolio NOT migrated — that is v0.60g2

lib/storage/investigation-storage.js

@@ -2,7 +2,7 @@
 // Owns the canonical identity contract: snapshot.id is the sole save identity.
 // Delegates to the concrete localStorage provider internally.
 
-import { loadInvestigation as _load, saveInvestigation as _save, clearInvestigation as _clear } from "./providers/local-storage.js";
+import { loadInvestigation as _load, saveInvestigation as _save, clearInvestigation as _clear, listInvestigations as _list } from "./providers/local-storage.js";
 
 /**
  * Canonical save contract: snapshot.id is the sole identity authority.
@@ -32,3 +32,11 @@ export function loadInvestigation(id) {
 export function clearInvestigation(id) {
   return _clear(id ?? undefined);
 }
+
+/**
+ * Lists all durable-ID Investigation records as lightweight summaries.
+ * Excludes legacy singleton, sessionStorage state, unrelated storage, malformed entries.
+ */
+export function listInvestigations() {
+  return _list();
+}

lib/storage/providers/local-storage.js

@@ -126,6 +126,55 @@ export function clearInvestigation(id) {
   }
 }
 
+// ── listInvestigations (durable-ID only) ───────────────────────
+
+/**
+ * Enumerates all durable-ID Investigation records and returns lightweight summaries.
+ * Skips malformed entries; excludes legacy singleton, sessionStorage state, unrelated keys.
+ */
+export function listInvestigations() {
+  const storage = _getTargetStorage();
+  if (!storage) return [];
+
+  const summaries = [];
+
+  for (let i = 0; i < storage.length; i++) {
+    const key = storage.key(i);
+    if (!key || !key.startsWith(INVESTIGATION_PREFIX)) continue;
+
+    try {
+      const raw = safeGet(storage, key);
+      if (!raw) continue;
+      const record = JSON.parse(raw);
+      if (!isPlainObject(record)) continue;
+      if (!record.id) continue;
+
+      summaries.push({
+        id: record.id,
+        scenario: record.scenario ?? null,
+        updatedAt: record.updatedAt ?? null,
+        investigationRevision: record.investigationRevision ?? 0,
+        reportExists: !!record.investigationReport,
+        reportGeneratedFromRevision: record.investigationReport
+          ? record.investigationReport.generatedFromRevision ?? null
+          : null,
+      });
+    } catch (_) {
+      // Malformed durable-ID entry — skip silently
+    }
+  }
+
+  summaries.sort((a, b) => {
+    const ta = a.updatedAt ?? "";
+    const tb = b.updatedAt ?? "";
+    if (ta > tb) return -1;
+    if (ta < tb) return 1;
+    return a.id > b.id ? -1 : 1;
+  });
+
+  return summaries;
+}
+
 // ── internals ────────────────────────────────────────────────────────
 
 function _persist(storage, key, value) {