Docs: warn bare-metal users about stale files when upgrading (#13296)

docs/administration.md

@@ -151,6 +151,23 @@ the background.
 
 ### Bare Metal Route {#bare-metal-updating}
 
+!!! warning
+
+    Extracting a new release archive on top of an existing installation
+    (e.g. `tar -xf paperless-ngx-vX.Y.Z.tar.xz -C /opt/paperless`) only adds
+    and overwrites files -- it does not remove files that were deleted in
+    the new release. Leftover files from an old version, such as
+    superseded database migrations, can remain on disk and cause errors
+    like `NodeNotFoundError` during `manage.py migrate`.
+
+    Before unpacking a new release over an existing bare-metal
+    installation, remove the previous source tree first (everything
+    except your `media`, `data`, and `consume` directories and your
+    `paperless.conf`/`.env`), or unpack into a fresh directory and move
+    your persistent data and configuration over. Installations updated via
+    `git pull` on a clean checkout are not affected, since Git removes
+    files that no longer exist upstream.
+
 After grabbing the new release and unpacking the contents, do the
 following:
 

docs/setup.md

@@ -262,6 +262,14 @@ to a positive number to enable polling and disable native filesystem notificatio
     and copy the contents to the home directory of the user you created
     earlier (`/opt/paperless`).
 
+    !!! note
+
+        If you are updating an existing bare-metal installation rather than
+        installing for the first time, see the
+        [bare metal update instructions](administration.md#bare-metal-updating)
+        instead -- extracting a new release on top of an old one can leave
+        behind stale files from the previous version.
+
     Optional: If you cloned the Git repository, you will need to
     compile the frontend yourself. See [here](development.md#front-end-development)
     and use the `build` step, not `serve`.