fix(core): resolve all 12 adversarial review findings

- Zeroize passwords in CLI prompts, handlers, and mount authentication
- Preserve carrier_node_id when recovering Slot 0 via recovery key
- Add --slot parameter to restore-header for targeted slot recovery
- Implement online_backup and restore_from_backup using SQLite Online Backup API
- Expose 'sanctum backup' and 'sanctum restore' CLI subcommands
- Fix inactivity auto-lock by removing touch() from PROPFIND metadata/read_dir
- Support O_APPEND by setting file cursor to file size on handle creation
- Prevent data loss by implementing Drop for CarrierFile to flush dirty blocks
- Optimize CSPRNG padding to only fill unwritten slack space
- Batch carrier initialization in 500-block transactions to prevent UI/CLI freeze
- Enforce 64-byte savings threshold for LZ4 compression
- Add WebClient service diagnostic hint for Windows net use mount errors
- Add unit and integration tests covering all new features

src/carrier.rs

@@ -178,10 +178,9 @@ pub fn write_carrier_block(
 
     let inner_ct_len = inner_ct.len() as u32;
 
-    // 2. Äußere Nutzlast vorbereiten: Exakt CHUNK_SIZE (1 MB) mit CSPRNG-Rauschen
+    // 2. Äußere Nutzlast vorbereiten: Exakt CHUNK_SIZE (1 MB)
     // Format: inner_nonce (12B) || inner_tag (16B) || inner_ct_len (4B LE) || inner_ct || CSPRNG-Padding
     let mut outer_plaintext = vec![0u8; CHUNK_SIZE];
-    OsRng.fill_bytes(&mut outer_plaintext);
 
     outer_plaintext[0..12].copy_from_slice(&inner_nonce);
     outer_plaintext[12..28].copy_from_slice(&inner_tag);
@@ -197,6 +196,11 @@ pub fn write_carrier_block(
     }
     outer_plaintext[32..ct_end].copy_from_slice(&inner_ct);
 
+    // Nur den ungenutzten Slack-Space mit kryptografischem Zufall auffüllen (~30x schneller als 1MB OsRng)
+    if ct_end < CHUNK_SIZE {
+        OsRng.fill_bytes(&mut outer_plaintext[ct_end..]);
+    }
+
     // 3. Äußere Schicht verschlüsseln (mit dek_outer = DEK_0)
     let (outer_ct, outer_nonce, outer_tag) = encrypt_chunk(
         dek_outer,
@@ -491,7 +495,7 @@ impl DavFileSystem for CarrierFs {
 
             drop(inner);
 
-            let file = CarrierFile::new(inode, self.inner.clone());
+            let file = CarrierFile::new(inode, self.inner.clone(), options.append);
             Ok(Box::new(file) as Box<dyn DavFile>)
         })
     }
@@ -502,7 +506,6 @@ impl DavFileSystem for CarrierFs {
         _meta: ReadDirMeta,
     ) -> FsFuture<'a, FsStream<Box<dyn DavDirEntry>>> {
         Box::pin(async move {
-            self.touch();
             let path_str = Self::path_to_str(path);
             let inner = self.inner.lock().unwrap();
 
@@ -537,9 +540,6 @@ impl DavFileSystem for CarrierFs {
     fn metadata<'a>(&'a self, path: &'a DavPath) -> FsFuture<'a, Box<dyn DavMetaData>> {
         Box::pin(async move {
             let path_str = Self::path_to_str(path);
-            if path_str != "/" && !path_str.is_empty() {
-                self.touch();
-            }
 
             let inner = self.inner.lock().unwrap();
             let node = inner.resolve_path(&path_str).ok_or(FsError::NotFound)?;
@@ -755,7 +755,7 @@ impl Debug for CarrierFile {
 }
 
 impl CarrierFile {
-    pub fn new(inode: CarrierInode, inner_fs: Arc<Mutex<CarrierFsInner>>) -> Self {
+    pub fn new(inode: CarrierInode, inner_fs: Arc<Mutex<CarrierFsInner>>, append: bool) -> Self {
         let meta = SanctumMetaData {
             is_dir: inode.is_dir,
             size: inode.size,
@@ -763,10 +763,12 @@ impl CarrierFile {
             modified_at: UNIX_EPOCH + Duration::from_secs(inode.modified_at),
         };
 
+        let cursor = if append { inode.size } else { 0 };
+
         Self {
             inode_id: inode.id,
             file_size: inode.size,
-            cursor: 0,
+            cursor,
             blocks: inode.blocks,
             inner_fs,
             meta,
@@ -991,3 +993,23 @@ impl DavFile for CarrierFile {
         })
     }
 }
+
+impl Drop for CarrierFile {
+    fn drop(&mut self) {
+        if let Err(e) = self.flush_cached_block() {
+            tracing::warn!("Fehler beim automatischen Flush im CarrierFile::drop: {:?}", e);
+        }
+        let now = SystemTime::now()
+            .duration_since(UNIX_EPOCH)
+            .map(|d| d.as_secs())
+            .unwrap_or(0);
+        if let Ok(mut inner) = self.inner_fs.lock() {
+            if let Some(inode) = inner.manifest.inodes.get_mut(&self.inode_id) {
+                inode.size = self.file_size;
+                inode.blocks = self.blocks.clone();
+                inode.modified_at = now;
+            }
+            let _ = inner.save_manifest();
+        }
+    }
+}