chore: import upstream snapshot with attribution

app/api/upload-binary/route.js

@@ -0,0 +1,53 @@
+import { NextResponse } from 'next/server';
+import { validateUploadProxyTarget } from '../../../src/lib/uploadProxyTarget';
+
+export async function POST(request) {
+    try {
+        const formData = await request.formData();
+
+        // Extract the original S3 target URL we injected earlier
+        const targetUrl = formData.get('x-proxy-target-url');
+
+        if (!targetUrl) {
+            return NextResponse.json({ error: 'Missing proxy target URL' }, { status: 400 });
+        }
+
+        const validatedTarget = validateUploadProxyTarget(targetUrl);
+        if (!validatedTarget.ok) {
+            return NextResponse.json(
+                { error: 'Invalid upload target', reason: validatedTarget.reason },
+                { status: 400 }
+            );
+        }
+
+        // Reconstruct the FormData for S3 (excluding our internal proxy marker)
+        const s3FormData = new FormData();
+        
+        // S3 is very sensitive to field ordering. We must ensure 'file' is likely last
+        // or at least that all signature fields come before what S3 expects.
+        // The original library code appends 'file' last, so iterating should preserve that.
+        for (const [key, value] of formData.entries()) {
+            if (key !== 'x-proxy-target-url') {
+                s3FormData.append(key, value);
+            }
+        }
+
+        // Perform the server-to-server POST to S3
+        // This bypasses browser CORS/Preflight security entirely
+        const s3Response = await fetch(validatedTarget.url, {
+            method: 'POST',
+            body: s3FormData,
+        });
+
+        if (s3Response.ok || s3Response.status === 204) {
+            return new Response(null, { status: 204 });
+        } else {
+            const errorText = await s3Response.text();
+            console.error('S3 Proxy Error:', errorText);
+            return new Response(errorText, { status: s3Response.status });
+        }
+    } catch (error) {
+        console.error('Upload Proxy Exception:', error);
+        return NextResponse.json({ error: error.message }, { status: 500 });
+    }
+}