feat: 1-to-1 message render + web data-lake backend

frontend/src/lib/stores/accounts.svelte.ts

@@ -0,0 +1,66 @@
+import { browser } from "$app/environment";
+import { listAccounts } from "$lib/api/endpoints";
+import type { Account } from "$lib/api/types";
+
+const STORAGE_KEY = "bg.account";
+
+function readSelected(): number | null {
+  if (!browser) {
+    return null;
+  }
+  const stored = localStorage.getItem(STORAGE_KEY);
+  return stored === null ? null : Number(stored);
+}
+
+function createAccounts() {
+  let list = $state<Account[]>([]);
+  let selectedId = $state<number | null>(readSelected());
+  let loaded = $state(false);
+
+  const selected = $derived(
+    list.find((account) => account.account_id === selectedId) ?? null
+  );
+
+  function persist(id: number | null) {
+    if (!browser) {
+      return;
+    }
+    if (id === null) {
+      localStorage.removeItem(STORAGE_KEY);
+    } else {
+      localStorage.setItem(STORAGE_KEY, String(id));
+    }
+  }
+
+  return {
+    get list() {
+      return list;
+    },
+    get selectedId() {
+      return selectedId;
+    },
+    get selected() {
+      return selected;
+    },
+    get loaded() {
+      return loaded;
+    },
+    async load() {
+      list = await listAccounts();
+      loaded = true;
+      const exists = list.some((account) => account.account_id === selectedId);
+      if (!exists) {
+        const fallback =
+          list.find((account) => account.is_active) ?? list.at(0) ?? null;
+        selectedId = fallback ? fallback.account_id : null;
+        persist(selectedId);
+      }
+    },
+    select(id: number) {
+      selectedId = id;
+      persist(id);
+    },
+  };
+}
+
+export const accounts = createAccounts();