fix(vfs): V-06 — sparse writes zero-fill gaps between previous end of file and seek offset

src/carrier.rs

@@ -1057,6 +1057,34 @@ impl DavFile for CarrierFile {
     fn write_bytes(&mut self, buf: Bytes) -> FsFuture<'_, ()> {
         self.touch();
         Box::pin(async move {
+            // V-06: Sparse Writes — Lücke zwischen bisherigem Dateiende und Cursor mit Nullen füllen
+            if self.cursor > self.file_size {
+                let target = self.cursor;
+                while self.file_size < target {
+                    let block_idx = (self.file_size / CARRIER_BLOCK_PAYLOAD_SIZE as u64) as usize;
+                    let offset_in_block = (self.file_size % CARRIER_BLOCK_PAYLOAD_SIZE as u64) as usize;
+                    let space_in_block = CARRIER_BLOCK_PAYLOAD_SIZE - offset_in_block;
+                    let to_pad = ((target - self.file_size) as usize).min(space_in_block);
+
+                    let block_data = self.ensure_block_loaded(block_idx)?;
+                    if block_data.len() < offset_in_block + to_pad {
+                        block_data.resize(offset_in_block + to_pad, 0);
+                    }
+
+                    let mut is_full = false;
+                    if let Some((_, ref d, ref mut dirty)) = self.cached_block {
+                        *dirty = true;
+                        is_full = d.len() >= CARRIER_BLOCK_PAYLOAD_SIZE;
+                    }
+
+                    self.file_size += to_pad as u64;
+
+                    if is_full {
+                        self.flush_cached_block()?;
+                    }
+                }
+            }
+
             let mut src = &buf[..];
 
             while !src.is_empty() {