feat(confidence-engine): use server investigation persistence

lib/storage/providers/server-http.js

@@ -0,0 +1,41 @@
+async function request(path, options) {
+  const response = await fetch(path, options);
+  const body = await response.json().catch(() => ({}));
+  if (!response.ok) {
+    throw new Error(body.error || "Investigation persistence request failed");
+  }
+  return body;
+}
+
+export async function saveInvestigation(snapshot, id) {
+  const body = await request("/api/investigations", {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify({ id, snapshot }),
+  });
+  return body.snapshot ?? null;
+}
+
+export async function loadInvestigation(id) {
+  const url = `/api/investigations/${encodeURIComponent(id)}`;
+  const response = await fetch(url);
+  if (!response.ok) {
+    if (response.status === 404) return null;
+    const body = await response.json().catch(() => ({}));
+    throw new Error(body.error || "Investigation persistence request failed");
+  }
+  const body = await response.json();
+  return body.snapshot ?? null;
+}
+
+export async function listInvestigations() {
+  const body = await request("/api/investigations");
+  return body.investigations ?? [];
+}
+
+export async function restartInvestigation(id) {
+  const body = await request(`/api/investigations/${encodeURIComponent(id)}/restart`, {
+    method: "POST",
+  });
+  return body.snapshot ?? null;
+}