fix: prevent SSE listener leak in console-logs stream (#751)

The ReadableStream cancel() callback is not reliably invoked on client
disconnect under Next.js, causing emitter listeners (line/clear) and the
keepalive interval to accumulate, eventually triggering
MaxListenersExceededWarning.

Use request.signal as the primary disconnect trigger, with cancel() and
enqueue failures as fallbacks. Cleanup is idempotent via state.closed.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/api/translator/console-logs/stream/route.js

@@ -4,10 +4,23 @@ export const dynamic = "force-dynamic";
 
 initConsoleLogCapture();
 
-export async function GET() {
+export async function GET(request) {
   const encoder = new TextEncoder();
   const emitter = getConsoleEmitter();
-  const state = { closed: false, send: null, keepalive: null };
+  const state = { closed: false, send: null, sendClear: null, keepalive: null };
+
+  // Idempotent: safe to call from request.signal abort, cancel(), or enqueue failure.
+  const cleanup = () => {
+    if (state.closed) return;
+    state.closed = true;
+    if (state.send) emitter.off("line", state.send);
+    if (state.sendClear) emitter.off("clear", state.sendClear);
+    if (state.keepalive) clearInterval(state.keepalive);
+  };
+
+  // request.signal fires reliably on client disconnect; ReadableStream.cancel()
+  // is not always invoked in Next.js, which caused listeners to accumulate.
+  request.signal.addEventListener("abort", cleanup, { once: true });
 
   const stream = new ReadableStream({
     start(controller) {
@@ -23,7 +36,7 @@ export async function GET() {
         try {
           controller.enqueue(encoder.encode(`data: ${JSON.stringify({ type: "line", line })}\n\n`));
         } catch {
-          state.closed = true;
+          cleanup();
         }
       };
 
@@ -33,7 +46,7 @@ export async function GET() {
         try {
           controller.enqueue(encoder.encode(`data: ${JSON.stringify({ type: "clear" })}\n\n`));
         } catch {
-          state.closed = true;
+          cleanup();
         }
       };
 
@@ -46,17 +59,13 @@ export async function GET() {
         try {
           controller.enqueue(encoder.encode(": ping\n\n"));
         } catch {
-          state.closed = true;
-          clearInterval(state.keepalive);
+          cleanup();
         }
       }, 25000);
     },
 
     cancel() {
-      state.closed = true;
-      emitter.off("line", state.send);
-      emitter.off("clear", state.sendClear);
-      clearInterval(state.keepalive);
+      cleanup();
     },
   });