tlc: Sprint 3 C15 — TarVfs::open rejects empty/garbage archives

The tar crate returns an empty iterator (without erroring) for
both zero-byte files and files that aren't valid tar archives.
TarVfs::open() previously succeeded in both cases, producing an
'unbrowsable' archive the user couldn't navigate.

Fix:
  TarVfs::open() now checks entries.is_empty() after list() and
  returns VfsError::Other('empty tar archive') when empty. This
  covers both truly empty files (corrupt/truncated) and garbage
  bytes (e.g., text mistakenly saved with .tar extension).

Tests (2 new in vfs::tar::tests):
  - tar_vfs_open_empty_file_errors
  - tar_vfs_open_garbage_bytes_errors

Total: 1281 passing (was 1279; +2 new).

local/recipes/tui/tlc/source/src/vfs/tar.rs

@@ -119,6 +119,13 @@ impl TarVfs {
             kinds: HashMap::new(),
         };
         me.list()?;
+        // An empty tar (zero entries) usually indicates a corrupt or
+        // truncated archive; the tar crate returns an empty
+        // iterator without erroring. Surface this as a real error
+        // so the caller doesn't present an unbrowsable archive.
+        if me.entries.is_empty() {
+            return Err(VfsError::Other("empty tar archive".to_string()));
+        }
         Ok(me)
     }
 
@@ -449,6 +456,29 @@ mod tests {
         assert!(r.is_err());
     }
 
+    #[test]
+    fn tar_vfs_open_empty_file_errors() {
+        // An empty file is not a valid tar archive; opening must
+        // return an error rather than silently producing an empty
+        // (unbrowsable) archive.
+        let p = std::env::temp_dir().join("tlc-tar-empty.tar");
+        std::fs::write(&p, b"").unwrap();
+        let r = TarVfs::open(p.clone());
+        assert!(r.is_err(), "empty file must error on TarVfs::open");
+        let _ = std::fs::remove_file(&p);
+    }
+
+    #[test]
+    fn tar_vfs_open_garbage_bytes_errors() {
+        // Random bytes that aren't a valid tar header must error
+        // rather than be silently accepted.
+        let p = std::env::temp_dir().join("tlc-tar-garbage.tar");
+        std::fs::write(&p, b"not a tar archive at all, just text").unwrap();
+        let r = TarVfs::open(p.clone());
+        assert!(r.is_err(), "garbage bytes must error on TarVfs::open");
+        let _ = std::fs::remove_file(&p);
+    }
+
     #[test]
     fn tar_vfs_extract_gz_round_trip() {
         let dir = std::env::temp_dir().join("tlc-tar-gz-test");