Scene Manager: request publishes missing on this site

- Request (globe) on casting rows and loaded assets whose latest publish
  is not on this site, and Request Missing for all of them, through the
  new wtdcmds command wtd_request_revisions. Requested publishes show
  "requested, waiting for the download".
- The version picker requests a version that is not on this site.
- A 404 explains that the session is gone or wtdcmds is too old.
- Fake server: car (vehicles) with a publish not on this site,
  wtd_request_revisions and /_test/download; 45 checks.
- Tested live: car_paul modeling.blend v001 -> Requested.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -346,8 +346,11 @@ Lists the assets cast in the shot, with how many instances are loaded out of how
 | ✔ | Loaded. |
 | Import arrow | Not loaded (or fewer instances than cast): click it to load this asset only. |
 | ⚠ red | Cannot be loaded, with the reason from Libreflow: not found in the flow, no published file, or nothing available on this site yet. |
+| Globe | The latest publish is not on this site: click it to request it (see below). |
+| Hourglass | Requested, waiting for the download. |
 
 - **Load Missing** links every cast asset that is not loaded yet, and adds the missing instances. Running it again only adds what is missing.
+- **Request Missing** (shown when needed) asks Libreflow to download, on this site, the latest publish of every cast or loaded asset that is not here yet: the same as **Request** in Libreflow (from the exchange site, or from the site that published it). The download is done by the Libreflow sync: click **Refresh** later, then load or update.
 - **Refresh** reads the casting and the versions again.
 - **Loaded, no longer cast** lists assets loaded earlier that the shot's casting no longer contains.
 
@@ -364,9 +367,9 @@ All of these can be changed in the [Configuration](#configuration).
 
 Lists everything the Scene Manager loaded, one line per asset, with its version:
 
-- The version is **red** when it is not the latest publish. The line under it says either "v004 available" (click the update icon), or "v004 published, not available on this site yet" (wait for the download).
+- The version is **red** when it is not the latest publish. The line under it says either "v004 available" (click the update icon), or "v004 published, not available on this site yet" (click the globe to request it, then "v004 requested, waiting for the download").
 - **Arrow**: shows the asset's instances, each with a button to select its objects and one to remove it.
-- **Menu icon**: pick another published version, for example to roll back. Versions not on this site are marked and cannot be picked.
+- **Menu icon**: pick another published version, for example to roll back. Versions not on this site are marked: picking one requests it; pick it again once it is downloaded.
 - **✕**: removes the asset entirely: all its instances and the link to its file.
 - **Update All** / **Update Selected**: switch all the loaded assets (or the ones of the selected objects) to their latest available publish.
 - **Remove Selected**: removes the instances of the selected objects.
@@ -463,7 +466,10 @@ Start Libreflow (with the `wtdcmds` extension), then click the refresh icon of t
 Its red line says why. "No file matching..." means none of its files matches `SCENE_MANAGER_FILE_PATTERNS`. "No collection named..." means the file has none of `COL_<asset>`, `<asset>` or `environments`, and several top-level collections: rename the published collection, or add its name to `SCENE_MANAGER_COLLECTION_NAMES`.
 
 **Scene Manager: the version stays red after Update.**
-The newer version is published but not downloaded on this site yet. Wait for the sync, then update again.
+The newer version is published but not downloaded on this site yet. Request it (globe icon) if it is not requested yet, wait for the sync, then refresh and update again.
+
+**Scene Manager: "...its wtdcmds extension is too old".**
+Libreflow runs an older `wtdcmds` without the command (e.g. requests). Update the extension and restart Libreflow.
 
 **Shot Viewer: playback only plays one shot.**
 **Loop Shot** is on. Untick it to play the whole sequence.