fix: follow a link anywhere under the store base

tests/link_store.rs

@@ -282,3 +282,27 @@ fn two_checkouts_of_one_remote_keep_their_own_files() {
     assert_eq!(fs::read(second.path(".env")).unwrap(), b"SECOND\n");
     second.ahab(&["link", "list"]).ok().says("linked:    .env");
 }
+
+#[test]
+fn a_link_into_an_older_store_layout_still_checks_clean_and_restores() {
+    let case = Case::new("legacy");
+    // the flat layout, before the store was keyed by checkout
+    let old = case.store.parent().unwrap().join(".env");
+    fs::create_dir_all(old.parent().unwrap()).unwrap();
+    fs::write(&old, b"SECRET=1\n").unwrap();
+    case.link(&case.path(".env"), &old);
+    case.gitignore(".env\n");
+
+    case.ahab(&["link", "check", "--exit-code"]).ok();
+    case.ahab(&["link", "restore", ".env"]).ok();
+
+    assert!(!case.is_symlink(".env"));
+    assert_eq!(fs::read(case.path(".env")).unwrap(), b"SECRET=1\n");
+    assert!(!old.exists());
+
+    // a link that leaves the store altogether is still refused
+    case.link(&case.path("key"), &case.outside.join("key"));
+    case.ahab(&["link", "restore", "key"])
+        .failed()
+        .says("not in the store");
+}