feat(chat): add Edge TTS playback

src/app/api/tts/edge/route.ts

@@ -0,0 +1,76 @@
+import { NextResponse } from "next/server";
+import { Communicate } from "edge-tts-ts";
+
+export const runtime = "nodejs";
+export const dynamic = "force-dynamic";
+
+const DEFAULT_VOICE = process.env.EDGE_TTS_VOICE || "zh-CN-XiaoxiaoNeural";
+const MAX_TEXT_LENGTH = 12000;
+
+type EdgeTtsRequest = {
+  text?: unknown;
+  voice?: unknown;
+};
+
+const jsonError = (message: string, status: number) =>
+  NextResponse.json({ error: message }, { status });
+
+export async function POST(request: Request) {
+  let payload: EdgeTtsRequest;
+  try {
+    payload = (await request.json()) as EdgeTtsRequest;
+  } catch {
+    return jsonError("Invalid JSON body", 400);
+  }
+
+  const text = typeof payload.text === "string" ? payload.text.trim() : "";
+  if (!text) {
+    return jsonError("text is required", 400);
+  }
+  if (text.length > MAX_TEXT_LENGTH) {
+    return jsonError(`text must be ${MAX_TEXT_LENGTH} characters or fewer`, 413);
+  }
+
+  const voice =
+    typeof payload.voice === "string" && payload.voice.trim()
+      ? payload.voice.trim()
+      : DEFAULT_VOICE;
+
+  try {
+    const communicate = new Communicate(text, { voice });
+    const chunks: Uint8Array[] = [];
+    let byteLength = 0;
+
+    for await (const chunk of communicate.stream()) {
+      if (chunk.type !== "audio") continue;
+      chunks.push(chunk.data);
+      byteLength += chunk.data.byteLength;
+    }
+
+    if (byteLength === 0) {
+      return jsonError("Edge TTS returned empty audio", 502);
+    }
+
+    const audio = new Uint8Array(byteLength);
+    let offset = 0;
+    for (const chunk of chunks) {
+      audio.set(chunk, offset);
+      offset += chunk.byteLength;
+    }
+
+    const audioBuffer = audio.buffer.slice(
+      audio.byteOffset,
+      audio.byteOffset + audio.byteLength,
+    );
+
+    return new Response(audioBuffer, {
+      headers: {
+        "Content-Type": "audio/mpeg",
+        "Cache-Control": "no-store",
+      },
+    });
+  } catch (error) {
+    console.error("[EdgeTTS] Failed to synthesize speech:", error);
+    return jsonError("Failed to synthesize speech", 502);
+  }
+}