Open write files with partial replacement writes

app/ServerUnit.js

@@ -73,7 +73,7 @@ class ServerUnit extends Unit {
         const placeholder = socket.session.temp_write_files?.[node.uuid] || await tmp.file()
         socket.session.temp_write_files[node.uuid] = placeholder
 
-        console.log('Upload placeholder!', placeholder)
+        console.log('Upload placeholder:', placeholder)
 
         const old_file = await node.uploaded_file()
         if ( old_file ) {
@@ -89,7 +89,7 @@ class ServerUnit extends Unit {
         console.log('write stream', stream)
         console.log('write data', { placeholder, position, length })
 
-        stream.pipe(fs.createWriteStream(placeholder.path, { start: position }))
+        stream.pipe(fs.createWriteStream(placeholder.path, { flags: 'r+', start: position }))
     }
 
     _bufferStream(stream) {