refactor(file|folder): separate etag and blob_hash

src/application/adapters/webdav_adapter.rs

@@ -444,9 +444,11 @@ impl WebDavAdapter {
         xml_writer.write_event(Event::Text(BytesText::new(&modified_at.to_rfc2822())))?;
         xml_writer.write_event(Event::End(BytesEnd::new("D:getlastmodified")))?;
 
-        // Other standard properties
+        // ETag — routes through `FolderDto::etag` (= `Folder::etag()`)
+        // so every WebDAV emitter and HEAD response agree on a single
+        // value for the same folder.
         xml_writer.write_event(Event::Start(BytesStart::new("D:getetag")))?;
-        xml_writer.write_event(Event::Text(BytesText::new(&format!("\"{}\"", folder.id))))?;
+        xml_writer.write_event(Event::Text(BytesText::new(&format!("\"{}\"", folder.etag))))?;
         xml_writer.write_event(Event::End(BytesEnd::new("D:getetag")))?;
 
         // Content length (0 for directories)
@@ -505,9 +507,11 @@ impl WebDavAdapter {
         xml_writer.write_event(Event::Text(BytesText::new(&modified_at.to_rfc2822())))?;
         xml_writer.write_event(Event::End(BytesEnd::new("D:getlastmodified")))?;
 
-        // ETag
+        // ETag — routes through `FileDto::etag` (= `File::etag()`) so
+        // PROPFIND, GET, HEAD, PUT-response, and MOVE all emit
+        // byte-identical values for the same file.
         xml_writer.write_event(Event::Start(BytesStart::new("D:getetag")))?;
-        xml_writer.write_event(Event::Text(BytesText::new(&format!("\"{}\"", file.id))))?;
+        xml_writer.write_event(Event::Text(BytesText::new(&format!("\"{}\"", file.etag))))?;
         xml_writer.write_event(Event::End(BytesEnd::new("D:getetag")))?;
 
         Ok(())
@@ -589,7 +593,7 @@ impl WebDavAdapter {
                         xml_writer.write_event(Event::Start(BytesStart::new("D:getetag")))?;
                         xml_writer.write_event(Event::Text(BytesText::new(&format!(
                             "\"{}\"",
-                            folder.id
+                            folder.etag
                         ))))?;
                         xml_writer.write_event(Event::End(BytesEnd::new("D:getetag")))?;
                     }
@@ -685,7 +689,7 @@ impl WebDavAdapter {
                         xml_writer.write_event(Event::Start(BytesStart::new("D:getetag")))?;
                         xml_writer.write_event(Event::Text(BytesText::new(&format!(
                             "\"{}\"",
-                            file.id
+                            file.etag
                         ))))?;
                         xml_writer.write_event(Event::End(BytesEnd::new("D:getetag")))?;
                     }

src/application/dtos/file_dto.rs

@@ -62,14 +62,32 @@ pub struct FileDto {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub sort_date: Option<u64>,
 
-    /// Content-addressable ETag (= blob_hash). Changes on every content write.
-    /// Used for WebDAV/Nextcloud ETag headers. Omitted from REST API JSON.
-    #[serde(skip)]
+    /// Raw BLAKE3 content hash. Populated from `File::content_hash()`.
+    /// Exposed in REST JSON so API consumers can use it for
+    /// content-addressable URLs, dedup verification, and integrity
+    /// audits. Distinct from `etag` (which is an HTTP-only cache
+    /// token whose formula may grow to include `modified_at` etc.).
+    pub content_hash: String,
+
+    /// Opaque HTTP ETag. Populated from `File::etag()`. Used by
+    /// WebDAV/NextCloud handlers when emitting `ETag` headers and
+    /// also exposed in REST JSON so frontends can pass it back
+    /// through `If-Match` / `If-None-Match` on download / mutation
+    /// endpoints without a separate HEAD round-trip.
     pub etag: String,
 }
 
 impl From<File> for FileDto {
     fn from(file: File) -> Self {
+        // Compute the HTTP ETag BEFORE consuming the entity — once
+        // `File::etag()` folds modified_at (and possibly more) into
+        // the formula, this becomes more than a string clone and
+        // must run against a live entity, not against
+        // already-extracted parts. content_hash is just the blob
+        // hash; etag is the cache token derived from it.
+        let etag = file.etag().to_string();
+        let content_hash = file.content_hash().to_string();
+
         // Consume the entity by moving all fields — zero heap allocations
         // for id, name, path, folder_id, owner_id (previously 5× .to_string()).
         let parts = file.into_parts();
@@ -95,7 +113,8 @@ impl From<File> for FileDto {
             size_formatted,
             owner_id: parts.owner_id.map(|u| u.to_string()),
             sort_date: None,
-            etag: parts.etag,
+            content_hash,
+            etag,
         }
     }
 }
@@ -150,6 +169,7 @@ impl FileDto {
             category: Arc::from("Document"),
             size_formatted: "0 Bytes".to_string(),
             owner_id: None,
+            content_hash: String::new(),
             etag: String::new(),
             sort_date: None,
         }

src/application/dtos/folder_dto.rs

@@ -73,11 +73,19 @@ pub struct FolderDto {
     /// Human-readable category (always "Folder")
     #[schema(value_type = String)]
     pub category: Arc<str>,
+
+    /// Opaque ETag for HTTP responses. Populated from `Folder::etag()`
+    /// at conversion time so every WebDAV / NextCloud handler emits
+    /// the same value, and exposed in REST JSON so the frontend can
+    /// pass it back through `If-Match` on rename / move endpoints
+    /// without a separate HEAD round-trip.
+    pub etag: String,
 }
 
 impl From<Folder> for FolderDto {
     fn from(folder: Folder) -> Self {
         let is_root = folder.parent_id().is_none();
+        let etag = folder.etag().to_string();
 
         Self {
             id: folder.id().to_string(),
@@ -91,6 +99,7 @@ impl From<Folder> for FolderDto {
             icon_class: Arc::from("fas fa-folder"),
             icon_special_class: Arc::from("folder-icon"),
             category: Arc::from("Folder"),
+            etag,
         }
     }
 }
@@ -141,6 +150,7 @@ impl FolderDto {
             icon_class: Arc::from("fas fa-folder"),
             icon_special_class: Arc::from("folder-icon"),
             category: Arc::from("Folder"),
+            etag: String::new(),
         }
     }
 }

src/application/services/trash_service.rs

@@ -809,8 +809,10 @@ fn build_trash_cursor(row: &TrashResourceRow, order_by: &str, reverse: bool) ->
 fn row_to_item_dto(row: TrashResourceRow) -> TrashResourceItemDto {
     let path = row.path.clone().unwrap_or_default();
     if row.resource_type == "folder" {
+        let resource_id = row.resource_id.to_string();
         let dto = FolderDto {
-            id: row.resource_id.to_string(),
+            etag: resource_id.clone(),
+            id: resource_id,
             name: row.name.clone(),
             path,
             parent_id: row.parent_id.map(|u| u.to_string()),
@@ -834,6 +836,8 @@ fn row_to_item_dto(row: TrashResourceRow) -> TrashResourceItemDto {
             .as_deref()
             .unwrap_or("application/octet-stream");
         let size_bytes = row.size.max(0) as u64;
+        // Trash listing row doesn't carry blob_hash either; trashed
+        // items aren't ETag-conditional in the UI.
         let dto = FileDto {
             id: row.resource_id.to_string(),
             name: row.name.clone(),
@@ -849,6 +853,7 @@ fn row_to_item_dto(row: TrashResourceRow) -> TrashResourceItemDto {
             size_formatted: format_file_size(size_bytes),
             owner_id: Some(row.owner_id.to_string()),
             sort_date: None,
+            content_hash: String::new(),
             etag: String::new(),
         };
         TrashResourceItemDto {

src/domain/entities/file.rs

@@ -21,7 +21,8 @@ pub struct FileParts {
     pub created_at: u64,
     pub modified_at: u64,
     pub owner_id: Option<Uuid>,
-    pub etag: String,
+    /// BLAKE3 content hash. See [`File::content_hash`] for semantics.
+    pub blob_hash: String,
 }
 
 /**
@@ -66,8 +67,14 @@ pub struct File {
     /// Owner user ID (from storage.files.user_id)
     owner_id: Option<Uuid>,
 
-    /// Content-addressable ETag (= blob_hash). Changes on every content write.
-    etag: String,
+    /// BLAKE3 content hash. Stable across renames/moves, changes only
+    /// when the file's content bytes change. Source of truth for both
+    /// content-addressable storage and the HTTP ETag (via
+    /// [`File::etag`]). Exposed publicly via [`File::content_hash`]
+    /// so the REST API can surface it as a distinct concept from the
+    /// ETag (the ETag formula may grow to include `modified_at` etc.,
+    /// but `content_hash` remains the raw hash).
+    blob_hash: String,
 }
 
 // We no longer need this module, now we use a String directly
@@ -85,7 +92,7 @@ impl Default for File {
             created_at: 0,
             modified_at: 0,
             owner_id: None,
-            etag: String::new(),
+            blob_hash: String::new(),
         }
     }
 }
@@ -123,7 +130,7 @@ impl File {
             created_at: now,
             modified_at: now,
             owner_id: None,
-            etag: String::new(),
+            blob_hash: String::new(),
         })
     }
 
@@ -154,7 +161,7 @@ impl File {
             created_at,
             modified_at,
             owner_id: None,
-            etag: String::new(),
+            blob_hash: String::new(),
         })
     }
 
@@ -170,7 +177,7 @@ impl File {
         modified_at: u64,
         owner_id: Option<Uuid>,
     ) -> FileResult<Self> {
-        Self::with_timestamps_and_etag(
+        Self::with_timestamps_and_blob_hash(
             id,
             name,
             storage_path,
@@ -185,7 +192,7 @@ impl File {
     }
 
     #[allow(clippy::too_many_arguments)]
-    pub fn with_timestamps_and_etag(
+    pub fn with_timestamps_and_blob_hash(
         id: String,
         name: String,
         storage_path: StoragePath,
@@ -195,7 +202,7 @@ impl File {
         created_at: u64,
         modified_at: u64,
         owner_id: Option<Uuid>,
-        etag: String,
+        blob_hash: String,
     ) -> FileResult<Self> {
         if let Err(reason) = validate_storage_name(&name) {
             return Err(FileError::InvalidFileName(format!("{name}: {reason}")));
@@ -215,7 +222,7 @@ impl File {
             created_at,
             modified_at,
             owner_id,
-            etag,
+            blob_hash,
         })
     }
 
@@ -235,12 +242,44 @@ impl File {
             created_at: self.created_at,
             modified_at: self.modified_at,
             owner_id: self.owner_id,
-            etag: self.etag,
+            blob_hash: self.blob_hash,
         }
     }
 
+    /// Raw BLAKE3 content hash — the cryptographic identity of the
+    /// file's bytes. Stable across renames, moves, and metadata
+    /// updates. Changes only when the underlying content changes.
+    ///
+    /// This is **distinct from [`File::etag`]**: the ETag is an HTTP
+    /// cache token that may incorporate non-content signals (mtime,
+    /// permissions, …) in future revisions; `content_hash` is the
+    /// raw hash, suitable for content-addressable URLs, dedup
+    /// verification, and integrity audits. Keep both accessible —
+    /// the API layer can choose to expose `content_hash` even when
+    /// `etag` grows additional inputs.
+    pub fn content_hash(&self) -> &str {
+        &self.blob_hash
+    }
+
+    /// Opaque HTTP ETag string (raw, NOT HTTP-quoted). Handlers wrap
+    /// in `"…"` themselves at the HTTP boundary.
+    ///
+    /// **Current formula**: equal to [`File::content_hash`] —
+    /// content-addressable BLAKE3. Stable across renames, changes on
+    /// every content write. Every handler that emits a file ETag
+    /// header MUST route through this method (or the matching
+    /// [`FileDto::etag`] field populated from it) so `GET`, `HEAD`,
+    /// `PROPFIND`, `PUT` response, and `MOVE` all return
+    /// byte-identical values for the same file.
+    ///
+    /// A follow-up PR will fold `modified_at` into the formula
+    /// (`{blob_hash[..16]}-{modified_at}`) so a `x-oc-mtime`-only
+    /// update (NextCloud preserves client mtime) invalidates client
+    /// caches even when the content bytes are unchanged. At that
+    /// point `etag()` and `content_hash()` diverge — that is the
+    /// reason they are exposed as two separate methods today.
     pub fn etag(&self) -> &str {
-        &self.etag
+        self.content_hash()
     }
 
     // Getters
@@ -310,7 +349,7 @@ impl File {
             created_at,
             modified_at,
             owner_id: None,
-            etag: String::new(),
+            blob_hash: String::new(),
         }
     }
 
@@ -348,7 +387,7 @@ impl File {
             created_at: self.created_at,
             modified_at: now,
             owner_id: self.owner_id,
-            etag: self.etag.clone(),
+            blob_hash: self.blob_hash.clone(),
         })
     }
 
@@ -383,7 +422,7 @@ impl File {
             created_at: self.created_at,
             modified_at: now,
             owner_id: self.owner_id,
-            etag: self.etag.clone(),
+            blob_hash: self.blob_hash.clone(),
         })
     }
 
@@ -405,7 +444,7 @@ impl File {
             created_at: self.created_at,
             modified_at: now,
             owner_id: self.owner_id,
-            etag: self.etag.clone(),
+            blob_hash: self.blob_hash.clone(),
         }
     }
 }
@@ -467,4 +506,53 @@ mod tests {
         assert_eq!(renamed.name(), "newname.txt");
         assert_eq!(renamed.id(), "123"); // The ID does not change
     }
+
+    /// Today `etag()` and `content_hash()` return the same string
+    /// (the v1 formula is identity); the test exists to catch a
+    /// future change that accidentally lets them disagree when they
+    /// should match. PR 2 will deliberately make them diverge.
+    #[test]
+    fn test_etag_currently_equals_content_hash() {
+        let file = File::with_timestamps_and_blob_hash(
+            "id-1".to_string(),
+            "file.txt".to_string(),
+            StoragePath::from_string("/file.txt"),
+            42,
+            "text/plain".to_string(),
+            None,
+            1_000,
+            2_000,
+            None,
+            "abcdef0123456789".to_string(),
+        )
+        .unwrap();
+
+        assert_eq!(file.content_hash(), "abcdef0123456789");
+        assert_eq!(file.etag(), file.content_hash());
+    }
+
+    /// Renames must NOT change the content identity. Both `etag()`
+    /// and `content_hash()` are derived from `blob_hash`, which is
+    /// preserved across `with_name`. If a future refactor drops
+    /// `blob_hash` from the rename builder, this test catches it.
+    #[test]
+    fn test_etag_stable_across_rename() {
+        let file = File::with_timestamps_and_blob_hash(
+            "id-1".to_string(),
+            "file.txt".to_string(),
+            StoragePath::from_string("/file.txt"),
+            42,
+            "text/plain".to_string(),
+            None,
+            1_000,
+            2_000,
+            None,
+            "stable-hash".to_string(),
+        )
+        .unwrap();
+
+        let renamed = file.with_name("renamed.txt".to_string()).unwrap();
+        assert_eq!(renamed.etag(), "stable-hash");
+        assert_eq!(renamed.content_hash(), "stable-hash");
+    }
 }

src/domain/entities/folder.rs

@@ -178,6 +178,29 @@ impl Folder {
         self.owner_id
     }
 
+    /// Opaque ETag string (raw, NOT HTTP-quoted). Handlers wrap in
+    /// `"…"` themselves at the HTTP boundary.
+    ///
+    /// **Current formula**: the folder's UUID — stable for the life of
+    /// the row, does NOT change when descendants are added/modified/
+    /// deleted. This matches today's behaviour in every existing
+    /// folder ETag emission site and is the de-facto v1 contract.
+    ///
+    /// **Known limitation**: NextCloud's sync engine relies on a
+    /// collection's ETag changing whenever any descendant changes —
+    /// that's the signal it uses to decide "recurse into this folder
+    /// to find what's new". A constant ETag breaks NC's incremental
+    /// sync (forces periodic deep recrawl).
+    ///
+    /// A follow-up PR will introduce `storage.folders.tree_modified_at`
+    /// (bumped by trigger on any descendant write) and switch this
+    /// method to `format!("{}-{}", id_short, tree_modified_at)`. That
+    /// PR will be ETag-breaking — all clients re-walk once — so it's
+    /// kept separate from this refactor.
+    pub fn etag(&self) -> &str {
+        &self.id
+    }
+
     /// Creates a new Folder instance from a DTO
     /// This function is primarily for conversions in batch handlers
     pub fn from_dto(

src/infrastructure/repositories/pg/file_blob_read_repository.rs

@@ -131,11 +131,11 @@ impl FileBlobReadRepository {
         mime_type: String,
         created_at: i64,
         modified_at: i64,
-        etag: String,
+        blob_hash: String,
         owner_id: Option<Uuid>,
     ) -> Result<File, DomainError> {
         let storage_path = Self::make_file_path(folder_path.as_deref(), &name);
-        File::with_timestamps_and_etag(
+        File::with_timestamps_and_blob_hash(
             id,
             name,
             storage_path,
@@ -145,7 +145,7 @@ impl FileBlobReadRepository {
             created_at as u64,
             modified_at as u64,
             owner_id,
-            etag,
+            blob_hash,
         )
         .map_err(|e| DomainError::internal_error("FileBlobRead", format!("entity: {e}")))
     }
@@ -226,9 +226,9 @@ impl FileBlobReadRepository {
         let mut files = Vec::with_capacity(rows.len());
         let mut sort_dates = Vec::with_capacity(rows.len());
 
-        for (id, name, fid, fpath, size, mime, ca, ma, etag, uid, sd) in rows {
+        for (id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid, sd) in rows {
             files.push(Self::row_to_file(
-                id, name, fid, fpath, size, mime, ca, ma, etag, uid,
+                id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid,
             )?);
             sort_dates.push(sd);
         }
@@ -410,9 +410,11 @@ impl FileReadPort for FileBlobReadRepository {
         .map_err(|e| DomainError::internal_error("FileBlobRead", format!("list: {e}")))?;
 
         rows.into_iter()
-            .map(|(id, name, fid, fpath, size, mime, ca, ma, etag, uid)| {
-                Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, etag, uid)
-            })
+            .map(
+                |(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid)| {
+                    Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid)
+                },
+            )
             .collect()
     }
 
@@ -466,9 +468,11 @@ impl FileReadPort for FileBlobReadRepository {
         .map_err(|e| DomainError::internal_error("FileBlobRead", format!("list_for_owner: {e}")))?;
 
         rows.into_iter()
-            .map(|(id, name, fid, fpath, size, mime, ca, ma, etag, uid)| {
-                Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, etag, uid)
-            })
+            .map(
+                |(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid)| {
+                    Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid)
+                },
+            )
             .collect()
     }
 
@@ -532,9 +536,11 @@ impl FileReadPort for FileBlobReadRepository {
         .map_err(|e| DomainError::internal_error("FileBlobRead", format!("list_batch: {e}")))?;
 
         rows.into_iter()
-            .map(|(id, name, fid, fpath, size, mime, ca, ma, etag, uid)| {
-                Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, etag, uid)
-            })
+            .map(
+                |(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid)| {
+                    Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid)
+                },
+            )
             .collect()
     }
 
@@ -598,9 +604,11 @@ impl FileReadPort for FileBlobReadRepository {
         })?;
 
         rows.into_iter()
-            .map(|(id, name, fid, fpath, size, mime, ca, ma, etag, uid)| {
-                Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, etag, uid)
-            })
+            .map(
+                |(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid)| {
+                    Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid)
+                },
+            )
             .collect()
     }
 
@@ -815,9 +823,9 @@ impl FileReadPort for FileBlobReadRepository {
             while let Some(row) = row_stream.try_next().await.map_err(|e| {
                 DomainError::internal_error("FileBlobRead", format!("subtree stream: {e}"))
             })? {
-                let (id, name, fid, fpath, size, mime, ca, ma, etag, uid) = row;
+                let (id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid) = row;
                 let file = FileBlobReadRepository::row_to_file(
-                    id, name, fid, fpath, size, mime, ca, ma, etag, uid,
+                    id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid,
                 )?;
                 yield file;
             }
@@ -930,8 +938,8 @@ impl FileReadPort for FileBlobReadRepository {
         let files = rows
             .into_iter()
             .map(
-                |(id, name, fid, fpath, size, mime, ca, ma, etag, uid, _total)| {
-                    Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, etag, uid)
+                |(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid, _total)| {
+                    Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid)
                 },
             )
             .collect::<Result<Vec<_>, _>>()
@@ -1116,8 +1124,8 @@ impl FileReadPort for FileBlobReadRepository {
         let files = rows
             .into_iter()
             .map(
-                |(id, name, fid, fpath, size, mime, ca, ma, etag, uid, _total)| {
-                    Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, etag, uid)
+                |(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid, _total)| {
+                    Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid)
                 },
             )
             .collect::<Result<Vec<_>, _>>()
@@ -1212,9 +1220,11 @@ impl FileReadPort for FileBlobReadRepository {
         .map_err(|e| DomainError::internal_error("FileBlobRead", format!("suggest: {e}")))?;
 
         rows.into_iter()
-            .map(|(id, name, fid, fpath, size, mime, ca, ma, etag, uid)| {
-                Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, etag, uid)
-            })
+            .map(
+                |(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid)| {
+                    Self::row_to_file(id, name, fid, fpath, size, mime, ca, ma, blob_hash, uid)
+                },
+            )
             .collect()
     }
 }

src/infrastructure/repositories/pg/file_blob_write_repository.rs

@@ -101,10 +101,10 @@ impl FileBlobWriteRepository {
         created_at: i64,
         modified_at: i64,
         owner_id: Option<Uuid>,
-        etag: String,
+        blob_hash: String,
     ) -> Result<File, DomainError> {
         let storage_path = Self::make_file_path(folder_path.as_deref(), &name);
-        File::with_timestamps_and_etag(
+        File::with_timestamps_and_blob_hash(
             id,
             name,
             storage_path,
@@ -114,7 +114,7 @@ impl FileBlobWriteRepository {
             created_at as u64,
             modified_at as u64,
             owner_id,
-            etag,
+            blob_hash,
         )
         .map_err(|e| DomainError::internal_error("FileBlobWrite", format!("entity: {e}")))
     }

src/infrastructure/services/path_resolver_service.rs

@@ -145,6 +145,7 @@ impl PathResolverService {
 
         match resource_type.as_str() {
             "folder" => Ok(ResolvedResource::Folder(FolderDto {
+                etag: id.clone(),
                 id,
                 name: name.clone(),
                 path: res_path,
@@ -160,6 +161,11 @@ impl PathResolverService {
             _ => {
                 let mime = mime_type.unwrap_or_else(|| "application/octet-stream".to_string());
                 let sz = size.unwrap_or(0) as u64;
+                // `content_hash`/`etag` are empty here: this resolver
+                // path doesn't select `blob_hash` from SQL — callers
+                // are doing existence/type discrimination, not ETag
+                // emission. If a caller ever needs an ETag from this
+                // codepath, widen the SELECT and populate properly.
                 Ok(ResolvedResource::File(FileDto {
                     id,
                     name: name.clone(),
@@ -175,6 +181,7 @@ impl PathResolverService {
                     size_formatted: format_file_size(sz),
                     owner_id: uid,
                     sort_date: None,
+                    content_hash: String::new(),
                     etag: String::new(),
                 }))
             }

src/interfaces/api/handlers/favorites_handler.rs

@@ -253,8 +253,10 @@ pub async fn list_favorites_resources(
                     };
 
                     if row.resource_type == "folder" {
+                        let resource_id = row.resource_id.to_string();
                         let dto = FolderDto {
-                            id: row.resource_id.to_string(),
+                            etag: resource_id.clone(),
+                            id: resource_id,
                             name: row.name.clone(),
                             path,
                             parent_id: row.parent_id.map(|u| u.to_string()),
@@ -277,6 +279,12 @@ pub async fn list_favorites_resources(
                             .as_deref()
                             .unwrap_or("application/octet-stream");
                         let size_bytes = row.size.max(0) as u64;
+                        // The favorites list query doesn't select
+                        // `blob_hash` — favorites UI displays metadata
+                        // only and doesn't trigger ETag-conditional
+                        // requests against these rows. If a caller
+                        // ever needs the content hash here, widen the
+                        // favorites SQL.
                         let dto = FileDto {
                             id: row.resource_id.to_string(),
                             name: row.name.clone(),
@@ -294,6 +302,7 @@ pub async fn list_favorites_resources(
                             size_formatted: format_file_size(size_bytes),
                             owner_id: Some(row.owner_id.to_string()),
                             sort_date: None,
+                            content_hash: String::new(),
                             etag: String::new(),
                         };
                         FavoritesResourceItemDto {

src/interfaces/api/handlers/folder_handler.rs

@@ -692,8 +692,10 @@ pub async fn list_folder_resources(
                 .into_iter()
                 .map(|row| {
                     if row.resource_type == "folder" {
+                        let resource_id = row.id.to_string();
                         let dto = FolderDto {
-                            id: row.id.to_string(),
+                            etag: resource_id.clone(),
+                            id: resource_id,
                             name: row.name.clone(),
                             path: String::new(), // cleared — share recipients must not see hierarchy
                             parent_id: row.parent_id.map(|u| u.to_string()),
@@ -715,6 +717,14 @@ pub async fn list_folder_resources(
                             .as_deref()
                             .unwrap_or("application/octet-stream");
                         let size_bytes = row.size.max(0) as u64;
+                        // `FolderResourceRow` (the UNION ALL row used
+                        // by this listing) doesn't carry `blob_hash`,
+                        // so neither `content_hash` nor `etag` can be
+                        // populated here without widening the SQL. The
+                        // REST file-listing UI doesn't issue
+                        // conditional requests against these rows —
+                        // file download / WebDAV PROPFIND go through
+                        // paths that DO carry the hash.
                         let dto = FileDto {
                             id: row.id.to_string(),
                             name: row.name.clone(),
@@ -730,6 +740,7 @@ pub async fn list_folder_resources(
                             size_formatted: format_file_size(size_bytes),
                             owner_id: Some(row.owner_id.to_string()),
                             sort_date: None,
+                            content_hash: String::new(),
                             etag: String::new(),
                         };
                         FolderResourceItemDto {

src/interfaces/api/handlers/recent_handler.rs

@@ -283,8 +283,10 @@ pub async fn list_recent_resources(
                     };
 
                     if row.resource_type == "folder" {
+                        let resource_id = row.resource_id.to_string();
                         let dto = FolderDto {
-                            id: row.resource_id.to_string(),
+                            etag: resource_id.clone(),
+                            id: resource_id,
                             name: row.name.clone(),
                             path,
                             parent_id: row.parent_id.map(|u| u.to_string()),
@@ -307,6 +309,8 @@ pub async fn list_recent_resources(
                             .as_deref()
                             .unwrap_or("application/octet-stream");
                         let size_bytes = row.size.max(0) as u64;
+                        // Recents listing row doesn't carry blob_hash
+                        // (same reason as folder_handler / favorites).
                         let dto = FileDto {
                             id: row.resource_id.to_string(),
                             name: row.name.clone(),
@@ -324,6 +328,7 @@ pub async fn list_recent_resources(
                             size_formatted: format_file_size(size_bytes),
                             owner_id: Some(row.owner_id.to_string()),
                             sort_date: None,
+                            content_hash: String::new(),
                             etag: String::new(),
                         };
                         RecentResourceItemDto {

src/interfaces/api/handlers/webdav_handler.rs

@@ -353,6 +353,7 @@ async fn handle_propfind(
         // Root folder
         let root_folder = FolderDto {
             id: "root".to_string(),
+            etag: "root".to_string(),
             name: "".to_string(),
             path: "".to_string(),
             parent_id: None,
@@ -706,7 +707,7 @@ async fn handle_get(
         .status(StatusCode::OK)
         .header(header::CONTENT_TYPE, &*file.mime_type)
         .header(header::CONTENT_LENGTH, file.size)
-        .header(header::ETAG, format!("\"{}\"", file.id))
+        .header(header::ETAG, format!("\"{}\"", file.etag))
         .header(
             header::LAST_MODIFIED,
             chrono::DateTime::<Utc>::from_timestamp(file.created_at as i64, 0)
@@ -747,7 +748,7 @@ async fn handle_head(
                     .status(StatusCode::OK)
                     .header(header::CONTENT_TYPE, "httpd/unix-directory")
                     .header(header::CONTENT_LENGTH, 0)
-                    .header(header::ETAG, format!("\"{}\"", folder.id))
+                    .header(header::ETAG, format!("\"{}\"", folder.etag))
                     .body(Body::empty())
                     .unwrap());
             }
@@ -756,7 +757,7 @@ async fn handle_head(
                     .status(StatusCode::OK)
                     .header(header::CONTENT_TYPE, &*file.mime_type)
                     .header(header::CONTENT_LENGTH, file.size)
-                    .header(header::ETAG, format!("\"{}\"", file.id))
+                    .header(header::ETAG, format!("\"{}\"", file.etag))
                     .header(
                         header::LAST_MODIFIED,
                         chrono::DateTime::<Utc>::from_timestamp(file.created_at as i64, 0)
@@ -777,7 +778,7 @@ async fn handle_head(
             .status(StatusCode::OK)
             .header(header::CONTENT_TYPE, "httpd/unix-directory")
             .header(header::CONTENT_LENGTH, 0)
-            .header(header::ETAG, format!("\"{}\"", folder.id))
+            .header(header::ETAG, format!("\"{}\"", folder.etag))
             .body(Body::empty())
             .unwrap());
     }
@@ -793,7 +794,7 @@ async fn handle_head(
         .status(StatusCode::OK)
         .header(header::CONTENT_TYPE, &*file.mime_type)
         .header(header::CONTENT_LENGTH, file.size)
-        .header(header::ETAG, format!("\"{}\"", file.id))
+        .header(header::ETAG, format!("\"{}\"", file.etag))
         .header(
             header::LAST_MODIFIED,
             chrono::DateTime::<Utc>::from_timestamp(file.created_at as i64, 0)

src/interfaces/nextcloud/report_handler.rs

@@ -250,6 +250,9 @@ async fn handle_search(
 
 /// Build a `FileDto` from a search file result.
 fn file_dto_from_search(fr: &crate::application::dtos::search_dto::SearchFileResultDto) -> FileDto {
+    // `SearchFileResultDto` doesn't carry `blob_hash`; the SEARCH /
+    // REPORT XML emitter doesn't read `content_hash` or `etag` off
+    // these DTOs anyway, so leaving them empty here is correct.
     FileDto {
         id: fr.id.clone(),
         name: fr.name.clone(),
@@ -267,6 +270,7 @@ fn file_dto_from_search(fr: &crate::application::dtos::search_dto::SearchFileRes
         size_formatted: format_file_size(fr.size),
         owner_id: None,
         sort_date: None,
+        content_hash: String::new(),
         etag: String::new(),
     }
 }
@@ -276,6 +280,7 @@ fn folder_dto_from_search(
     sr: &crate::application::dtos::search_dto::SearchFolderResultDto,
 ) -> FolderDto {
     FolderDto {
+        etag: sr.id.clone(),
         id: sr.id.clone(),
         name: sr.name.clone(),
         path: sr.path.clone(),

src/interfaces/nextcloud/webdav_handler.rs

@@ -348,11 +348,18 @@ async fn handle_get(
         chrono::DateTime::<Utc>::from_timestamp(timestamp_to_i64(file.modified_at), 0)
             .unwrap_or_else(Utc::now);
 
+    // ETag comes from `FileDto::etag` (populated from `File::etag()`
+    // in the `From<File>` impl) — single source of truth, so GET,
+    // HEAD, PUT-response, MOVE, and PROPFIND all emit byte-identical
+    // values for the same file. NC's sync engine compares cached
+    // PROPFIND ETags against GET/HEAD responses; using `file.id` here
+    // (a UUID) while PROPFIND emitted the blob hash made NC see
+    // every file as "remotely changed" on first descent.
     Ok(Response::builder()
         .status(StatusCode::OK)
         .header(header::CONTENT_TYPE, file.mime_type.as_ref())
         .header(header::CONTENT_LENGTH, file.size)
-        .header(header::ETAG, format!("\"{}\"", file.id))
+        .header(header::ETAG, format!("\"{}\"", file.etag))
         .header(header::LAST_MODIFIED, modified_at.to_rfc2822())
         .body(Body::from_stream(std::pin::Pin::from(stream)))
         .unwrap())
@@ -400,11 +407,14 @@ async fn handle_head(
         chrono::DateTime::<Utc>::from_timestamp(timestamp_to_i64(file.modified_at), 0)
             .unwrap_or_else(Utc::now);
 
+    // ETag comes from `FileDto::etag` — see the same comment block on
+    // the GET handler. HEAD and GET must agree byte-for-byte; pulling
+    // both from the same DTO field guarantees that.
     Ok(Response::builder()
         .status(StatusCode::OK)
         .header(header::CONTENT_TYPE, file.mime_type.as_ref())
         .header(header::CONTENT_LENGTH, file.size)
-        .header(header::ETAG, format!("\"{}\"", file.id))
+        .header(header::ETAG, format!("\"{}\"", file.etag))
         .header(header::LAST_MODIFIED, modified_at.to_rfc2822())
         .body(Body::empty())
         .unwrap())
@@ -850,9 +860,13 @@ async fn handle_move(
         let dest_internal = nc_to_internal_path(&user.username, &dest_subpath)?;
         let mut builder = Response::builder().status(StatusCode::CREATED);
         if let Ok(moved) = file_service.get_file_by_path(&dest_internal).await {
+            // Route through `FileDto::etag` so the MOVE response
+            // matches what a subsequent PROPFIND on the destination
+            // will return — `moved.id` (UUID) would differ from the
+            // blob hash and trigger NC's "remote changed" detection.
             builder = builder
-                .header(header::ETAG, format!("\"{}\"", moved.id))
-                .header("oc-etag", format!("\"{}\"", moved.id));
+                .header(header::ETAG, format!("\"{}\"", moved.etag))
+                .header("oc-etag", format!("\"{}\"", moved.etag));
         }
 
         return Ok(builder.body(Body::empty()).unwrap());
@@ -1094,7 +1108,10 @@ pub fn write_folder_response<W: std::io::Write>(
             .unwrap_or_else(Utc::now);
 
     write_text_element(xml, "d:getlastmodified", &modified_at.to_rfc2822())?;
-    write_text_element(xml, "d:getetag", &format!("\"{}\"", folder.id))?;
+    // Route through `FolderDto::etag` (= `Folder::etag()`, currently
+    // the folder UUID — see the entity for the documented v1 formula
+    // and the follow-up plan to make it descendant-aware).
+    write_text_element(xml, "d:getetag", &format!("\"{}\"", folder.etag))?;
     write_text_element(xml, "d:getcontenttype", "httpd/unix-directory")?;
     write_text_element(xml, "d:getcontentlength", "0")?;
     write_text_element(xml, "d:creationdate", &created_at.to_rfc3339())?;

static/js/core/types.js

@@ -25,6 +25,7 @@
  * @property {string} owner_id
  * @property {string|null} parent_id the folder parent (null if is_root)
  * @property {string} path the full path
+ * @property {string} etag opaque HTTP ETag, for If-Match / If-None-Match
  */
 
 //FIXME: rename into FileItem
@@ -44,6 +45,8 @@
  * @property {number} size
  * @property {string} size_formatted
  * @property {number} sort_date
+ * @property {string} etag opaque HTTP ETag, for If-Match / If-None-Match
+ * @property {string} content_hash raw BLAKE3 content hash, for dedup checks
  */
 
 /**

static/js/views/favorites/favoritesView.js

@@ -377,7 +377,8 @@ const favoritesView = {
                         sort_date: toSecs(item.favorited_at),
                         icon_class: f.icon_class,
                         icon_special_class: f.icon_special_class ?? '',
-                        category: 'Folder'
+                        category: 'Folder',
+                        etag: ''
                     })
                 );
             } else if (item.resource_type === 'file') {
@@ -397,7 +398,9 @@ const favoritesView = {
                         sort_date: toSecs(item.favorited_at),
                         icon_class: f.icon_class,
                         icon_special_class: f.icon_special_class ?? '',
-                        category: f.category
+                        category: f.category,
+                        etag: '',
+                        content_hash: ''
                     })
                 );
             }

static/js/views/recent/recentView.js

@@ -384,7 +384,8 @@ const recentView = {
                         sort_date: toSecs(item.accessed_at),
                         icon_class: f.icon_class,
                         icon_special_class: f.icon_special_class ?? '',
-                        category: 'Folder'
+                        category: 'Folder',
+                        etag: ''
                     })
                 );
             } else if (item.resource_type === 'file') {
@@ -404,7 +405,9 @@ const recentView = {
                         sort_date: toSecs(item.accessed_at),
                         icon_class: f.icon_class,
                         icon_special_class: f.icon_special_class ?? '',
-                        category: f.category
+                        category: f.category,
+                        etag: '',
+                        content_hash: ''
                     })
                 );
             }

static/js/views/sharedWithMe/sharedWithMeView.js

@@ -386,7 +386,8 @@ const sharedWithMeView = {
                         sort_date: grantedAtSecs(item.granted_at),
                         icon_class: f.icon_class,
                         icon_special_class: f.icon_special_class ?? '',
-                        category: 'folder'
+                        category: 'folder',
+                        etag: ''
                     })
                 );
             } else if (item.resource_type === 'file') {
@@ -406,7 +407,9 @@ const sharedWithMeView = {
                         sort_date: grantedAtSecs(item.granted_at),
                         icon_class: f.icon_class,
                         icon_special_class: f.icon_special_class ?? '',
-                        category: f.category
+                        category: f.category,
+                        etag: '',
+                        content_hash: ''
                     })
                 );
             }

static/js/views/trash/trashView.js

@@ -393,7 +393,8 @@ const trashView = {
                         deletion_date: item.deletion_date,
                         icon_class: f.icon_class,
                         icon_special_class: f.icon_special_class ?? '',
-                        category: 'Folder'
+                        category: 'Folder',
+                        etag: ''
                     })
                 );
             } else if (item.resource_type === 'file') {
@@ -417,7 +418,9 @@ const trashView = {
                         deletion_date: item.deletion_date,
                         icon_class: f.icon_class,
                         icon_special_class: f.icon_special_class ?? '',
-                        category: f.category
+                        category: f.category,
+                        etag: '',
+                        content_hash: ''
                     })
                 );
             }