Fix SSE proxy: create Next.js route handlers for all streaming endpoints

Next.js rewrites() buffer HTTP responses and drop long-lived connections,
making SSE (text/event-stream) impossible. The backend never even received
the request (no log entry in API, ECONNRESET in web proxy logs).

Create dedicated route.ts files for all 3 SSE endpoints:
- /api/v1/ppt/outlines/stream/[id]
- /api/v1/ppt/presentation/stream/[id]
- /api/v1/ppt/jobs/[job_id]/stream

Each route forwards cookies for auth and returns backend's ReadableStream
directly as a Response, preventing any buffering. Sets X-Accel-Buffering: no
to also disable nginx buffering.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/app/api/v1/ppt/jobs/[job_id]/stream/route.ts

@@ -0,0 +1,44 @@
+/**
+ * SSE Proxy for job progress stream.
+ * Next.js rewrites() don't handle SSE (text/event-stream) — they buffer responses
+ * and drop long-lived connections. This route handler streams directly without buffering.
+ */
+import { NextRequest } from 'next/server';
+
+export const dynamic = 'force-dynamic';
+
+const API_URL = process.env.API_INTERNAL_URL || 'http://api:8000';
+
+export async function GET(
+  request: NextRequest,
+  { params }: { params: { job_id: string } }
+) {
+  try {
+    const backendResponse = await fetch(
+      `${API_URL}/api/v1/ppt/jobs/${params.job_id}/stream`,
+      {
+        headers: {
+          Cookie: request.headers.get('cookie') || '',
+          Accept: 'text/event-stream',
+          'Cache-Control': 'no-cache',
+        },
+      }
+    );
+
+    if (!backendResponse.ok || !backendResponse.body) {
+      return new Response(null, { status: backendResponse.status });
+    }
+
+    return new Response(backendResponse.body, {
+      headers: {
+        'Content-Type': 'text/event-stream',
+        'Cache-Control': 'no-cache, no-transform',
+        'X-Accel-Buffering': 'no',
+        'Connection': 'keep-alive',
+      },
+    });
+  } catch (error) {
+    console.error('[SSE] jobs/stream error:', error);
+    return new Response(null, { status: 502 });
+  }
+}

frontend/app/api/v1/ppt/outlines/stream/[id]/route.ts

@@ -0,0 +1,44 @@
+/**
+ * SSE Proxy for outline generation stream.
+ * Next.js rewrites() don't handle SSE (text/event-stream) — they buffer responses
+ * and drop long-lived connections. This route handler streams directly without buffering.
+ */
+import { NextRequest } from 'next/server';
+
+export const dynamic = 'force-dynamic';
+
+const API_URL = process.env.API_INTERNAL_URL || 'http://api:8000';
+
+export async function GET(
+  request: NextRequest,
+  { params }: { params: { id: string } }
+) {
+  try {
+    const backendResponse = await fetch(
+      `${API_URL}/api/v1/ppt/outlines/stream/${params.id}`,
+      {
+        headers: {
+          Cookie: request.headers.get('cookie') || '',
+          Accept: 'text/event-stream',
+          'Cache-Control': 'no-cache',
+        },
+      }
+    );
+
+    if (!backendResponse.ok || !backendResponse.body) {
+      return new Response(null, { status: backendResponse.status });
+    }
+
+    return new Response(backendResponse.body, {
+      headers: {
+        'Content-Type': 'text/event-stream',
+        'Cache-Control': 'no-cache, no-transform',
+        'X-Accel-Buffering': 'no',
+        'Connection': 'keep-alive',
+      },
+    });
+  } catch (error) {
+    console.error('[SSE] outlines/stream error:', error);
+    return new Response(null, { status: 502 });
+  }
+}

frontend/app/api/v1/ppt/presentation/stream/[id]/route.ts

@@ -0,0 +1,44 @@
+/**
+ * SSE Proxy for presentation generation stream.
+ * Next.js rewrites() don't handle SSE (text/event-stream) — they buffer responses
+ * and drop long-lived connections. This route handler streams directly without buffering.
+ */
+import { NextRequest } from 'next/server';
+
+export const dynamic = 'force-dynamic';
+
+const API_URL = process.env.API_INTERNAL_URL || 'http://api:8000';
+
+export async function GET(
+  request: NextRequest,
+  { params }: { params: { id: string } }
+) {
+  try {
+    const backendResponse = await fetch(
+      `${API_URL}/api/v1/ppt/presentation/stream/${params.id}`,
+      {
+        headers: {
+          Cookie: request.headers.get('cookie') || '',
+          Accept: 'text/event-stream',
+          'Cache-Control': 'no-cache',
+        },
+      }
+    );
+
+    if (!backendResponse.ok || !backendResponse.body) {
+      return new Response(null, { status: backendResponse.status });
+    }
+
+    return new Response(backendResponse.body, {
+      headers: {
+        'Content-Type': 'text/event-stream',
+        'Cache-Control': 'no-cache, no-transform',
+        'X-Accel-Buffering': 'no',
+        'Connection': 'keep-alive',
+      },
+    });
+  } catch (error) {
+    console.error('[SSE] presentation/stream error:', error);
+    return new Response(null, { status: 502 });
+  }
+}