core: add the disinherit directive to stop the parent cascade

README.md

@@ -212,6 +212,9 @@ one directive per line, `#` are comments
 # keeping variables inherited from parent .cade layers
 pure
 
+# stop the cascade here; no parent .cade layers load above this dir
+disinherit
+
 # load from flake (default shell or named installable)
 load
 load flake

src/cli/parse.rs

@@ -62,6 +62,7 @@ impl FromStr for Keyword {
 
         let res = match keyword.as_str() {
             "pure" => Pure,
+            "disinherit" => Disinherit,
             "call" => {
                 // split respecting shell quoting
                 let target = shlex::split(rest_raw).ok_or(ParseError::InvalidQuoting)?;
@@ -181,6 +182,14 @@ mod tests {
         ));
     }
 
+    #[test]
+    fn bare_disinherit_parses() {
+        assert!(matches!(
+            "disinherit".parse::<Keyword>(),
+            Ok(Keyword::Disinherit)
+        ));
+    }
+
     #[test]
     fn keyword_with_equals_in_args_stays_a_keyword() {
         // the `=` belongs to the hook command, not a bare assignment