fix+test: check hash ref count on copy-on-write (a duplicated beeing updated)

src/application/ports/blob_lifecycle.rs

@@ -0,0 +1,21 @@
+use std::future::Future;
+use std::pin::Pin;
+
+/// Observer notified by [`DedupService`] when a blob's ref_count reaches zero
+/// and it is permanently removed from storage.
+///
+/// Implement this trait on any service that needs to react to blob deletion
+/// (e.g. thumbnail cleanup, CDN invalidation, audit logging).  Register with
+/// [`DedupService::add_blob_hook`] during DI wiring.
+///
+/// The boxed-future return keeps the trait dyn-compatible so multiple
+/// implementations can be stored as `Vec<Arc<dyn BlobDeletionHook>>`.
+pub trait BlobDeletionHook: Send + Sync {
+    /// Called after the blob file has been removed from disk.
+    /// `blob_hash` is the BLAKE3 hex string identifying the blob.
+    /// Must be best-effort — must not propagate errors.
+    fn on_blob_deleted<'a>(
+        &'a self,
+        blob_hash: &'a str,
+    ) -> Pin<Box<dyn Future<Output = ()> + Send + 'a>>;
+}

src/application/services/trash_service.rs

@@ -61,6 +61,7 @@ pub struct TrashService {
 }
 
 impl TrashService {
+    #[allow(clippy::too_many_arguments)]
     pub fn new(
         trash_repository: Arc<TrashDbRepository>,
         file_read_port: Arc<FileBlobReadRepository>,