feat: migrate graph snapshot handling to localStorage for improved persistence

src/lib/db.js

@@ -293,44 +293,52 @@ export function setSetting(key, value) {
 
 // ── Graph Snapshots ───────────────────────────────────────────────────────────
 //
-// A single "latest" snapshot is persisted in the settings collection before
-// every bulk graph write. This survives browser/tab close and lets the admin
-// roll back an AI analysis that produced unwanted results.
+// Stored in localStorage, not in PocketBase.
 //
-// The value is stored as a JSON string because the settings collection only
-// has a plain text `value` field. Large graphs (150+ topics) can produce
-// ~100 KB of JSON, which SQLite handles without issue.
+// The settings collection's `value` field is a plain text field designed for
+// small strings (model overrides, flags). A full graph snapshot can easily
+// reach 40–100 KB of JSON, which causes a 400 Bad Request from PocketBase.
+//
+// localStorage is the right choice here: the admin who clicks "Analyze" and
+// the admin who clicks "Restore" are always the same person, on the same
+// machine, in the same browser. Cross-device persistence is not required.
 
-const SNAPSHOT_KEY = 'graph_snapshot:latest';
+const SNAPSHOT_LS_KEY = 'respellion:graph_snapshot';
 
 /**
- * Persist the current graph state as a rollback point.
+ * Persist the current graph state as a rollback point in localStorage.
  * Called by useGraphData.bulkSave() before overwriting the graph.
  *
- * @param {object[]} topics    — the graph state to preserve
- * @param {object[]} relations — the graph state to preserve
+ * Silently no-ops if localStorage is unavailable (private browsing quota
+ * exceeded, etc.) — the snapshot is best-effort, not critical-path.
+ *
+ * @param {object[]} topics
+ * @param {object[]} relations
  */
-export async function saveGraphSnapshot(topics, relations) {
-  const payload = JSON.stringify({
-    ts: Date.now(),
-    topicCount: topics.length,
-    relationCount: relations.length,
-    topics,
-    relations,
-  });
-  return setSetting(SNAPSHOT_KEY, payload);
+export function saveGraphSnapshot(topics, relations) {
+  try {
+    localStorage.setItem(SNAPSHOT_LS_KEY, JSON.stringify({
+      ts: Date.now(),
+      topicCount: topics.length,
+      relationCount: relations.length,
+      topics,
+      relations,
+    }));
+  } catch {
+    // Storage quota exceeded or unavailable — skip silently.
+  }
 }
 
 /**
- * Read the latest snapshot back from PocketBase.
- * Returns null when no snapshot exists or the stored value is malformed.
+ * Read the latest snapshot from localStorage.
+ * Returns null when nothing is stored or the value is malformed.
  *
  * @returns {{ ts: number, topicCount: number, relationCount: number, topics: object[], relations: object[] } | null}
  */
-export async function getGraphSnapshot() {
-  const raw = await getSetting(SNAPSHOT_KEY, null);
-  if (!raw) return null;
+export function getGraphSnapshot() {
   try {
+    const raw = localStorage.getItem(SNAPSHOT_LS_KEY);
+    if (!raw) return null;
     return JSON.parse(raw);
   } catch {
     return null;
@@ -338,11 +346,13 @@ export async function getGraphSnapshot() {
 }
 
 /**
- * Delete the stored snapshot (e.g. after a successful restore so the
- * admin cannot accidentally restore twice).
+ * Remove the stored snapshot after a successful restore so the admin cannot
+ * accidentally restore twice.
  */
 export function clearGraphSnapshot() {
-  return setSetting(SNAPSHOT_KEY, '');
+  try {
+    localStorage.removeItem(SNAPSHOT_LS_KEY);
+  } catch { /* non-fatal */ }
 }
 
 // ── Curriculum Versions (v2) ──────────────────────────────────────────────────