fix(blobs): invalidate the file_id->blob_hash cache on content swaps

The read repository's hash_cache assumed blob hashes were immutable
per file_id, but update_file_content_from_temp remaps the SAME row to
a new hash via swap_blob_hash. After a WebDAV/NC PUT overwrite,
streaming downloads (>=10 MB tier, Range requests, video playback)
kept resolving the OLD blob for the 30 s TTI window — and because
every read refreshes the TTI, a polling client could pin the stale
mapping indefinitely, eventually turning into 500s once the old
blob's refcount hit zero and GC removed it.

The write repository now holds a shared handle to the same moka cache
(clones share storage) and invalidates the entry right after every
content swap and hard delete commits — covering every present and
future caller of the write port rather than one service path. Stale
doc comments claiming the mapping was immutable (and SHA-256) fixed.

https://claude.ai/code/session_01QxwJDHqQhbMkHK333QtMme

src/common/di.rs

@@ -380,6 +380,9 @@ impl AppServiceFactory {
                 db_pool.clone(),
                 core.dedup_service.clone(),
                 folder_repo_concrete.clone(),
+                // Shared blob-hash cache: the write side invalidates entries
+                // on content swaps/deletes so reads never serve stale blobs.
+                file_read_repository.blob_hash_cache(),
             ));
 
         // I18n repository — file-system backed, gated by the locale

src/infrastructure/repositories/pg/file_blob_read_repository.rs

@@ -59,8 +59,14 @@ pub struct FileBlobReadRepository {
     dedup: Arc<DedupService>,
     /// Lock-free cache: file_id → blob_hash.
     /// Populated by `get_file()` and `resolve_blob_hash()` (slow path).
-    /// Entries persist until TTI expiry (30 s idle) or capacity eviction —
-    /// safe because blob_hash is content-addressed and never mutated.
+    /// Entries persist until TTI expiry (30 s idle) or capacity eviction.
+    /// Content updates DO remap a file_id to a new hash in place
+    /// (`swap_blob_hash`), so the write repository shares this cache (see
+    /// [`Self::blob_hash_cache`]) and invalidates the entry on every
+    /// content swap and hard delete — without that, streaming downloads
+    /// kept serving the previous blob for the TTI window after a PUT
+    /// update (or 500'd once the old blob was garbage-collected), and
+    /// every read refreshed the TTI, extending the window indefinitely.
     hash_cache: Cache<String, String>,
 }
 
@@ -80,6 +86,14 @@ impl FileBlobReadRepository {
         }
     }
 
+    /// Shared handle to the file_id → blob_hash cache (moka clones share
+    /// the underlying storage). Handed to `FileBlobWriteRepository` at DI
+    /// time so content swaps and hard deletes invalidate the mapping the
+    /// moment they commit.
+    pub fn blob_hash_cache(&self) -> Cache<String, String> {
+        self.hash_cache.clone()
+    }
+
     /// Returns the user_id (owner) for a given file ID.
     /// Mirrors `FolderDbRepository::get_folder_user_id`.
     /// Used by the AuthorizationEngine for owner short-circuit.
@@ -157,9 +171,9 @@ impl FileBlobReadRepository {
     /// subsequent reads for the same file (e.g. Range Requests on a video,
     /// thumbnail + download, browser re-fetch) hit the cache instead of PG.
     ///
-    /// This is safe because `blob_hash` is content-addressed (SHA-256)
-    /// and never mutated — if the file's content changes, a new row with a
-    /// new `blob_hash` is created.
+    /// Staleness safety: content updates remap the file to a new hash in
+    /// place — the write repository invalidates this cache (shared via
+    /// [`Self::blob_hash_cache`]) right after every swap/delete commits.
     async fn resolve_blob_hash(&self, file_id: &str) -> Result<String, DomainError> {
         // Fast path: cached (lock-free read, refreshes TTI automatically)
         if let Some(hash) = self.hash_cache.get(file_id) {

src/infrastructure/repositories/pg/file_blob_write_repository.rs

@@ -7,6 +7,7 @@
 //! File paths are resolved by querying the materialized `storage.folders.path`
 //! column (O(1) per lookup), so no recursive CTEs are needed.
 
+use moka::sync::Cache;
 use sqlx::PgPool;
 use std::path::PathBuf;
 use std::sync::Arc;
@@ -26,6 +27,10 @@ pub struct FileBlobWriteRepository {
     pool: Arc<PgPool>,
     dedup: Arc<DedupService>,
     folder_repo: Arc<FolderDbRepository>,
+    /// Shared handle to `FileBlobReadRepository`'s file_id → blob_hash
+    /// cache. Content swaps and hard deletes invalidate the mapping here
+    /// so the read side can never serve a stale blob after a PUT update.
+    hash_cache: Cache<String, String>,
 }
 
 impl FileBlobWriteRepository {
@@ -33,11 +38,13 @@ impl FileBlobWriteRepository {
         pool: Arc<PgPool>,
         dedup: Arc<DedupService>,
         folder_repo: Arc<FolderDbRepository>,
+        hash_cache: Cache<String, String>,
     ) -> Self {
         Self {
             pool,
             dedup,
             folder_repo,
+            hash_cache,
         }
     }
 
@@ -54,6 +61,7 @@ impl FileBlobWriteRepository {
             ),
             dedup: Arc::new(DedupService::new_stub()),
             folder_repo: Arc::new(super::folder_db_repository::FolderDbRepository::new_stub()),
+            hash_cache: Cache::builder().max_capacity(10_000).build(),
         }
     }
 
@@ -502,6 +510,8 @@ impl FileWritePort for FileBlobWriteRepository {
             return Err(DomainError::not_found("File", id));
         }
 
+        // Drop the read-side file_id → blob_hash mapping for the dead row.
+        self.hash_cache.invalidate(id);
         Ok(())
     }
 
@@ -521,8 +531,14 @@ impl FileWritePort for FileBlobWriteRepository {
             .await?;
         let new_hash = dedup_result.hash().to_string();
 
-        self.swap_blob_hash(file_id, &new_hash, size as i64, modified_at)
-            .await
+        let swapped = self
+            .swap_blob_hash(file_id, &new_hash, size as i64, modified_at)
+            .await?;
+        // The file now maps to a different blob — drop the read-side cache
+        // entry so streaming downloads cannot serve the previous content
+        // for the rest of its TTI window.
+        self.hash_cache.invalidate(file_id);
+        Ok(swapped)
     }
 
     async fn register_file_deferred(