ui: read persisted settings before the API key probe (#27365)

The route loads run ahead of the root layout script, so validateApiKey
read the settings store while it still held factory defaults and probed
/props without the stored key. initStores() now hands the same startup
promise to every caller and the chat loads await it before probing.

The one-time admin baseline no longer overwrites a key the user has
already set: on a first visit the config carries factory values only, so
a diverging key comes from the user and wins.

tools/ui/src/lib/stores/init.ts

@@ -1,10 +1,15 @@
 /**
- * Explicit store initialization, called once from the root layout.
+ * Explicit store initialization, run once and shared by every caller.
  *
  * Order matters: migrations run first because they rename and rewrite
  * localStorage keys, so every store that reads localStorage initializes
  * only after they complete. Constructors and module-level side effects
  * stay empty so import order can no longer change startup behavior.
+ *
+ * The returned promise resolves once the persisted state is in memory, which
+ * route loads await before reading settings: they run ahead of the root layout
+ * script. The conversation list loads in the background, awaited by the chat
+ * page that renders it.
  */
 
 // direct imports, not via the barrel, to avoid circular deps
@@ -16,19 +21,20 @@ import { versionStore } from './version.svelte';
 import { browser } from '$app/environment';
 import { MigrationService } from '$lib/services/migration.service';
 
-let started = false;
+let startup: Promise<void> | null = null;
 
-export async function initStores(): Promise<void> {
-	if (!browser || started) return;
+export function initStores(): Promise<void> {
+	if (!browser) return Promise.resolve();
 
-	started = true;
+	startup ??= (async () => {
+		await MigrationService.runAllMigrations();
 
-	await MigrationService.runAllMigrations();
+		settingsStore.initialize();
+		permissionsStore.initialize();
+		toolsStore.initialize();
+		void versionStore.initialize();
+		void conversationsStore.init();
+	})();
 
-	settingsStore.initialize();
-	permissionsStore.initialize();
-	toolsStore.initialize();
-	void versionStore.initialize();
-
-	await conversationsStore.init();
+	return startup;
 }

tools/ui/src/lib/stores/settings.svelte.ts

@@ -358,17 +358,24 @@ class SettingsStore {
 		// UI settings are the admin's defaults for new users: applied once on
 		// the first visit, never on later loads, so the user's config can
 		// diverge. "Reset to Default" is the explicit way back to the baseline.
+		// A first visit config carries factory values only, so a key that
+		// already diverges here was set by the user before the baseline could
+		// be reached, through the API key splash, and stays theirs.
 		if (uiSettings && this.isFirstVisit) {
 			this.isFirstVisit = false;
 
 			for (const [key, value] of Object.entries(uiSettings)) {
-				if (!this.userOverrides.has(key) && value !== undefined) {
-					setConfigValue(this.config, key, value);
+				if (value === undefined || this.userOverrides.has(key)) continue;
 
-					// theme lives in mode-watcher, not just in config -> propagate
-					if (key === SETTINGS_KEYS.THEME) {
-						setMode(value as ColorMode);
-					}
+				if (getConfigValue(this.config, key) !== getConfigValue(SETTING_CONFIG_DEFAULT, key)) {
+					continue;
+				}
+
+				setConfigValue(this.config, key, value);
+
+				// theme lives in mode-watcher, not just in config -> propagate
+				if (key === SETTINGS_KEYS.THEME) {
+					setMode(value as ColorMode);
 				}
 			}
 		}