Wire SW update prompt and request persistent storage (M6, web.dev)

src/app/infrastructure/storage-persist.ts

@@ -0,0 +1,45 @@
+/**
+ * Persistent-storage request (web.dev → council; see reference/principles/web-dev.md).
+ *
+ * By default browser storage is **best-effort**: under storage pressure the
+ * browser may evict the whole origin's IndexedDB + Cache API data. For a
+ * local-first app whose workspace lives only in the browser, that is data loss.
+ * `navigator.storage.persist()` asks the browser not to evict us.
+ *
+ * Behaviour per web.dev guidance:
+ *   - feature-detect; do nothing where the API is absent (never throw),
+ *   - check `persisted()` first and request **at most once** — don't nag,
+ *   - stay silent on denial: Chromium decides automatically from heuristics
+ *     (installed / engagement / notifications), and there is nothing the user
+ *     can act on, so no toast.
+ *
+ * Browser-only; the rest of the app reaches it through `orchestration/pwa`.
+ */
+
+export type PersistResult =
+  | { supported: false }
+  | { supported: true; persisted: boolean; alreadyPersisted: boolean };
+
+/**
+ * Ensure persistent storage, requesting it once if not already granted.
+ * Resolves to the outcome; never rejects.
+ */
+export async function requestPersistentStorage(): Promise<PersistResult> {
+  const storage = typeof navigator !== 'undefined' ? navigator.storage : undefined;
+  if (
+    !storage ||
+    typeof storage.persist !== 'function' ||
+    typeof storage.persisted !== 'function'
+  ) {
+    return { supported: false };
+  }
+  try {
+    const alreadyPersisted = await storage.persisted();
+    if (alreadyPersisted) return { supported: true, persisted: true, alreadyPersisted: true };
+    const persisted = await storage.persist();
+    return { supported: true, persisted, alreadyPersisted: false };
+  } catch {
+    // A rejected request is not actionable by the user — report not-persisted.
+    return { supported: true, persisted: false, alreadyPersisted: false };
+  }
+}