Finish the mobile performance pass

- Cache the model catalog once per user and each conversation's setting
  separately; clear both on logout and after model saves
- Compress hashed assets asynchronously with a byte budget and set Vary
- Memoize message parsing and throttle selection reads
- Debounce draft writes to localStorage
- Keep the composer editor on the page and focused, as before
- Add a bundle budget check and run it in CI
- Show a loading block while sessions load and a workspace avatar in the
  mobile conversation header

src/utils/harness-cache.ts

@@ -0,0 +1,120 @@
+import { AppData } from "@/src/data/app-data";
+import type {
+    BotHarnessSettingsPayload,
+    HarnessCatalogPayload,
+} from "@/src/types";
+
+/**
+ * Bumped when a cached model payload changes shape, so an older cache is
+ * fetched again instead of read.
+ */
+const CacheVersion = 1;
+
+type CacheEnvelope<T> = {
+    v: number;
+    /**
+     * Unix ms it was fetched.
+     */
+    at: number;
+    data: T;
+};
+
+type UserKey = {
+    user_id: number | string;
+};
+
+type SettingsKey = UserKey & {
+    bot_id: number | string;
+    workspace_id?: number | null;
+};
+
+function catalogKey({ user_id }: UserKey) {
+    return `${AppData.HarnessCacheStorageKey}:catalog:${user_id}`;
+}
+
+function settingsKey({ user_id, bot_id, workspace_id }: SettingsKey) {
+    return `${AppData.HarnessCacheStorageKey}:settings:${user_id}:${bot_id}:${workspace_id || 0}`;
+}
+
+function read<T>(key: string): CacheEnvelope<T> | null {
+    try {
+        const cached = JSON.parse(localStorage.getItem(key) || "null");
+
+        return cached?.v == CacheVersion &&
+            typeof cached.at == "number" &&
+            Array.isArray(cached.data?.harnesses)
+            ? cached
+            : null;
+    } catch {
+        return null;
+    }
+}
+
+function write<T>(key: string, data: T) {
+    try {
+        localStorage.setItem(
+            key,
+            JSON.stringify({ v: CacheVersion, at: Date.now(), data } satisfies CacheEnvelope<T>),
+        );
+    } catch {}
+}
+
+/**
+ * The install-wide model catalog this user last fetched, from
+ * `localStorage`; null when there is none or it can't be read.
+ */
+export function readHarnessCatalogCache(key: UserKey) {
+    return read<HarnessCatalogPayload>(catalogKey(key));
+}
+
+export function writeHarnessCatalogCache({
+    user_id,
+    data,
+}: UserKey & { data: HarnessCatalogPayload }) {
+    write(catalogKey({ user_id }), data);
+}
+
+/**
+ * One conversation's model setting this user last fetched, from
+ * `localStorage`; null when there is none or it can't be read.
+ */
+export function readHarnessSettingsCache(key: SettingsKey) {
+    return read<BotHarnessSettingsPayload>(settingsKey(key));
+}
+
+export function writeHarnessSettingsCache({
+    user_id,
+    bot_id,
+    workspace_id,
+    data,
+}: SettingsKey & { data: BotHarnessSettingsPayload }) {
+    write(settingsKey({ user_id, bot_id, workspace_id }), data);
+}
+
+/**
+ * Drops every model cache, including the per-conversation keys an older
+ * version wrote. Called on logout and after model settings change
+ * elsewhere, so the modal can't show a stale pick.
+ */
+export function clearHarnessCache() {
+    const prefixes = [
+        AppData.HarnessCacheStorageKey,
+        AppData.LegacyHarnessOverviewStorageKey,
+    ];
+
+    try {
+        const keys: string[] = [];
+
+        for (let index = 0; index < localStorage.length; index++) {
+            const key = localStorage.key(index);
+
+            if (key) keys.push(key);
+        }
+
+        for (const key of keys) {
+            if (prefixes.some((prefix) => key.startsWith(prefix))) {
+                localStorage.removeItem(key);
+            }
+        }
+    } catch {}
+}