feat(tts): switch out retry for key:model rotation

app/api/tts/route.ts

@@ -10,9 +10,17 @@ const { DONATE_WIDGET_KEY, GEMINI_TTS_API_KEY } = process.env as Record<
   string
 >;
 
+const MODELS = [
+  "gemini-2.5-flash-preview-tts",
+  "gemini-3.1-flash-preview-tts",
+] as const;
 const API_KEYS = GEMINI_TTS_API_KEY.split(",")
   .map((k) => k.trim())
   .filter(Boolean);
+const POSSIBLE_CHOICES = MODELS.flatMap((m) =>
+  API_KEYS.map((k) => `${k}:${m}` as `${string}:${(typeof MODELS)[number]}`),
+);
+const MAX_TRIES = 10;
 
 const Schema = z.object({
   message: z.string().max(1000),
@@ -33,19 +41,33 @@ export async function GET(request: Request) {
 
   const textHash = hash(message).toString(36);
   const cached = await redis!.get(`tts:${textHash}`);
+  console.log(
+    `[TTS] ${textHash}:${cached ? "cached" : "fresh"} "${message.slice(0, 200)}${message.length > 200 ? "..." : ""}"`,
+  );
   if (cached)
     return new Response(pcmToWav(cached), {
       headers: { "Content-Type": "audio/wav" },
     });
 
   let audioData: string | undefined;
-
-  for (const apiKey of API_KEYS) {
+  let currentRotation = await redis!
+    .get("tts_key_rotation")
+    .then((e) => (e ? Number(e) : 0))
+    .catch(() => 0);
+  for (
+    let i = 0;
+    i < MAX_TRIES;
+    i++, currentRotation = (currentRotation + 1) % POSSIBLE_CHOICES.length
+  ) {
+    const [apiKey, model] = POSSIBLE_CHOICES[currentRotation].split(":");
+    console.log(
+      `[TTS] Trying key ${apiKey.slice(0, 8)}:${model} (${currentRotation}/${POSSIBLE_CHOICES} #${i + 1})...`,
+    );
     const client = new GoogleGenAI({ apiKey });
 
     try {
       const response = await client.models.generateContent({
-        model: "gemini-2.5-flash-preview-tts",
+        model,
         contents: [{ parts: [{ text: message }] }],
         config: {
           responseModalities: ["AUDIO"],
@@ -65,11 +87,13 @@ export async function GET(request: Request) {
       console.error(`TTS API key failed: ${apiKey.slice(0, 8)}...`, e);
     }
   }
+  console.log("[TTS] Got response?", audioData);
 
   if (!audioData)
     return Response.json({ error: "Response is empty" }, { status: 500 });
   queueMicrotask(() => {
     redis!.setex(`tts:${textHash}`, 604800, audioData);
+    redis!.setex("tts_key_rotation", 604800, `${currentRotation}`);
   });
   return new Response(pcmToWav(audioData), {
     headers: { "Content-Type": "audio/wav" },