test(remote): a download whose size nobody sent does not invent one

`install_phase_caption` is shared by the switcher's progress bar and the
strip's, precisely so a user watching both is not told two different things —
which also means a wrong caption is wrong in two places at once.

A server that sends no `content-length` gives `total: None`. Rendering that
through the with-total string reads "12 MB / 12 MB" while the transfer is
still running: it claims the download has finished, and the bar beside it
disagrees. Nothing failed when the two arms were swapped.

Held now across all four phases — no fraction when the size is unknown, one
when it is, an upload always knowing its total, and restarting having no
fraction at all.

src/ui/remote_workspace.rs

@@ -3309,4 +3309,42 @@ mod tests {
             );
         });
     }
+
+    /// A download whose size the server never sent does not invent one.
+    ///
+    /// `install_phase_caption` is shared by the switcher's bar and the strip's
+    /// so a user watching both is not told two different things — which makes
+    /// a wrong caption wrong in two places at once. A `None` total rendered
+    /// through the with-total string reads "12 MB / 12 MB" while the transfer
+    /// is still running: it claims the download is finished, and the bar
+    /// beside it disagrees.
+    #[test]
+    fn a_download_with_no_known_total_says_so() {
+        use crate::daemon::install::InstallPhase;
+
+        let unknown = install_phase_caption(InstallPhase::Downloading {
+            done: 12_000_000,
+            total: None,
+        });
+        assert!(
+            !unknown.contains('/'),
+            "a size nobody sent must not appear as a fraction: {unknown}"
+        );
+
+        let known = install_phase_caption(InstallPhase::Downloading {
+            done: 6_000_000,
+            total: Some(12_000_000),
+        });
+        assert!(
+            known.contains('/'),
+            "a size the server did send is shown as a fraction: {known}"
+        );
+        assert_ne!(known, unknown, "the two phases do not read the same");
+
+        // An upload always knows its total; restarting has no fraction at all.
+        let copying = install_phase_caption(InstallPhase::Uploading { done: 1, total: 2 });
+        assert!(copying.contains('/'), "{copying}");
+        let restarting = install_phase_caption(InstallPhase::Restarting);
+        assert!(!restarting.contains('/'), "{restarting}");
+    }
 }