fix(ui): use test-connection endpoint for TTS credential validation

Update CredentialsSection to call /v1/tts/test-connection instead of
/v1/tts/synthesize - allows testing unsaved credentials before save.

ui/web/src/pages/tts/hooks/use-tts-config.ts

@@ -52,6 +52,22 @@ export interface SynthesizeParams {
   model_id?: string;
 }
 
+export interface TestConnectionParams {
+  provider: string;
+  api_key?: string;
+  api_base?: string;
+  voice_id?: string;
+  model_id?: string;
+  group_id?: string;
+}
+
+export interface TestConnectionResult {
+  success: boolean;
+  provider?: string;
+  latency_ms?: number;
+  error?: string;
+}
+
 export function useTtsConfig() {
   const ws = useWs();
   const http = useHttp();
@@ -114,5 +130,22 @@ export function useTtsConfig() {
     [http],
   );
 
-  return { tts, loading, saving, error, refresh: invalidate, save, synthesize };
+  // Test connection with unsaved credentials — uses ephemeral provider.
+  const testConnection = useCallback(
+    async (params: TestConnectionParams): Promise<TestConnectionResult> => {
+      const res = await fetch("/v1/tts/test-connection", {
+        method: "POST",
+        headers: { "Content-Type": "application/json", ...http.getAuthHeaders() },
+        body: JSON.stringify(params),
+      });
+      const data = (await res.json()) as TestConnectionResult;
+      if (!res.ok || !data.success) {
+        throw new Error(data.error || `Test failed (${res.status})`);
+      }
+      return data;
+    },
+    [http],
+  );
+
+  return { tts, loading, saving, error, refresh: invalidate, save, synthesize, testConnection };
 }

ui/web/src/pages/tts/sections/credentials-section.tsx

@@ -13,7 +13,7 @@ import { Label } from "@/components/ui/label";
 import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
 import { toast } from "@/stores/use-toast-store";
 import { getProviderDefinition } from "@/data/tts-providers";
-import type { TtsConfig, TtsProviderConfig, SynthesizeParams } from "../hooks/use-tts-config";
+import type { TtsConfig, TtsProviderConfig, TestConnectionParams, TestConnectionResult } from "../hooks/use-tts-config";
 
 interface Props {
   provider: string;
@@ -22,10 +22,10 @@ interface Props {
     providerKey: keyof Pick<TtsConfig, "openai" | "elevenlabs" | "edge" | "minimax">,
     patch: Partial<TtsProviderConfig>,
   ) => void;
-  synthesize: (params: SynthesizeParams) => Promise<Blob>;
+  testConnection: (params: TestConnectionParams) => Promise<TestConnectionResult>;
 }
 
-export function CredentialsSection({ provider, draft, onUpdate, synthesize }: Props) {
+export function CredentialsSection({ provider, draft, onUpdate, testConnection }: Props) {
   const { t } = useTranslation("tts");
   const [testing, setTesting] = useState(false);
 
@@ -36,8 +36,18 @@ export function CredentialsSection({ provider, draft, onUpdate, synthesize }: Pr
   const handleTestConnection = async () => {
     setTesting(true);
     try {
-      await synthesize({ text: "Hello, this is a connection test.", provider });
-      toast.success(t("testConnection.success", "Connection successful"));
+      // Build params from draft credentials — test with unsaved config
+      const cfg = draft[provider as keyof Pick<typeof draft, "openai" | "elevenlabs" | "minimax">];
+      const params: TestConnectionParams = {
+        provider,
+        api_key: cfg?.api_key,
+        api_base: cfg?.api_base || cfg?.base_url,
+        voice_id: cfg?.voice_id || cfg?.voice,
+        model_id: cfg?.model_id || cfg?.model,
+        group_id: (cfg as { group_id?: string })?.group_id,
+      };
+      const result = await testConnection(params);
+      toast.success(t("testConnection.success", "Connection successful"), `${result.latency_ms}ms`);
     } catch (err) {
       const msg = err instanceof Error ? err.message : String(err);
       toast.error(t("testConnection.failed", "Connection failed"), msg);

ui/web/src/pages/tts/tts-page.tsx

@@ -68,7 +68,7 @@ function modelPatch(provider: string, value: string): [ProviderKey, Partial<TtsP
 export function TtsPage() {
   const { t } = useTranslation("tts");
   const { t: tc } = useTranslation("common");
-  const { tts, loading, saving, error, refresh, save, synthesize } = useTtsConfig();
+  const { tts, loading, saving, error, refresh, save, synthesize, testConnection } = useTtsConfig();
   const spinning = useMinLoading(loading);
 
   const [draft, setDraft] = useState<TtsConfig>(tts);
@@ -138,7 +138,7 @@ export function TtsPage() {
           provider={draft.provider}
           draft={draft}
           onUpdate={updateProvider}
-          synthesize={synthesize}
+          testConnection={testConnection}
         />
       )}