diff --git a/sandbox-sidecar/src/runners/e2bRunner.ts b/sandbox-sidecar/src/runners/e2bRunner.ts
index cb163b0fd..3b7d30ae4 100644
--- a/sandbox-sidecar/src/runners/e2bRunner.ts
+++ b/sandbox-sidecar/src/runners/e2bRunner.ts
@@ -207,7 +207,15 @@ export class E2BSandboxRunner implements SandboxRunner {
     // Write the config archive
     const archivePath = `${workDir}/bundle.tar.gz`;
     const archiveBuffer = Buffer.from(job.payload.configArchive, "base64");
-    await sandbox.files.write(archivePath, archiveBuffer.buffer);
+    
+    // IMPORTANT: Extract exact-sized ArrayBuffer to avoid writing extra padding bytes
+    // archiveBuffer.buffer can include unused bytes if the Buffer is a slice/view of a larger ArrayBuffer
+    // This was causing intermittent "gzip: invalid header" errors
+    const exactBuffer = archiveBuffer.buffer.slice(
+      archiveBuffer.byteOffset,
+      archiveBuffer.byteOffset + archiveBuffer.byteLength
+    );
+    await sandbox.files.write(archivePath, exactBuffer);
 
     // Extract the archive (excluding any existing state files to avoid conflicts)
     // Use gunzip + tar separately for better compatibility across tar versions
diff --git a/ui/src/components/UnitCreateForm.tsx b/ui/src/components/UnitCreateForm.tsx
index 4d6b9dbc8..d49369b7f 100644
--- a/ui/src/components/UnitCreateForm.tsx
+++ b/ui/src/components/UnitCreateForm.tsx
@@ -35,8 +35,9 @@ export default function UnitCreateForm({
   const [isCreating, setIsCreating] = React.useState(false)
   const [error, setError] = React.useState<string | null>(null)
   
-  // Remote runs beta is now always enabled
-  const remoteRunsEnabled = true
+  // Remote runs are gated by localStorage flag for beta testing
+  // Set localStorage.setItem('REMOTE_RUNS', 'true') to enable
+  const remoteRunsEnabled = typeof window !== 'undefined' && localStorage.getItem('REMOTE_RUNS') === 'true'
 
   const handleCreate = async () => {
     if (!unitName.trim()) return