hive-c0re: widen nix stderr predicate to cover error:/evaluation warning:, add tests

hive-c0re/src/lifecycle/tests.rs

@@ -421,3 +421,31 @@ fn ensure_state_dir_creates_the_work_dir() {
     assert!(notes_dir.is_dir());
     assert!(root.path().join(crate::paths::WORK_SUBDIR).is_dir());
 }
+
+/// Real build failures (`error:`) and both of nix's own warning spellings
+/// must stay WARN; routine progress chatter is the only thing demoted.
+/// Regression guard for a first-pass predicate that only matched
+/// `warning:` and silently buried `error:` lines at INFO.
+#[test]
+fn is_actionable_nix_line_keeps_warnings_and_errors_demotes_chatter() {
+    let actionable = [
+        "warning: Lock file entry is unlocked",
+        "  warning: leading whitespace",
+        "evaluation warning: this will be an error in a future release",
+        "error: builder for '/nix/store/foo.drv' failed with exit code 1",
+        "error: 1 dependencies of derivation '/nix/store/bar.drv' failed to build",
+    ];
+    for line in actionable {
+        assert!(is_actionable_nix_line(line), "{line}");
+    }
+
+    let chatter = [
+        "copying 3 paths",
+        "these 2 derivations will be built:",
+        "fetching git input 'git+file:///var/lib/hyperhive'",
+        "structuredAttrs is enabled",
+    ];
+    for line in chatter {
+        assert!(!is_actionable_nix_line(line), "{line}");
+    }
+}