feat(gui): error helper to classify zbus errors and produce user messages

gui/src/error.rs

@@ -0,0 +1,87 @@
+//! Map zbus errors to short, user-facing strings. The GUI surfaces these in
+//! `adw::Toast` and inside the touch-prompt dialog's failure state.
+//!
+//! Pure logic; testable without a display server.
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[allow(dead_code)] // wired through keys_page.rs / enroll_dialog.rs in Tasks 4-6.
+pub(crate) enum ErrorKind {
+    /// Daemon unreachable / bus dropped — caller should swap to disconnected banner.
+    Disconnected,
+    /// polkit denied. Daemon's message is usually fine to show verbatim.
+    AccessDenied,
+    /// Anything else — daemon returned a typed `Failed(msg)` or similar.
+    Other,
+}
+
+#[allow(dead_code)] // wired through keys_page.rs / enroll_dialog.rs in Tasks 4-6.
+pub(crate) fn classify(err: &zbus::Error) -> ErrorKind {
+    match err {
+        zbus::Error::InputOutput(_) | zbus::Error::Address(_) | zbus::Error::Handshake(_) => {
+            ErrorKind::Disconnected
+        }
+        zbus::Error::FDO(boxed) => match boxed.as_ref() {
+            zbus::fdo::Error::AccessDenied(_) => ErrorKind::AccessDenied,
+            zbus::fdo::Error::ServiceUnknown(_) | zbus::fdo::Error::NameHasNoOwner(_) => {
+                ErrorKind::Disconnected
+            }
+            _ => ErrorKind::Other,
+        },
+        _ => ErrorKind::Other,
+    }
+}
+
+#[allow(dead_code)] // wired through keys_page.rs / enroll_dialog.rs in Tasks 4-6.
+pub(crate) fn user_message(err: &zbus::Error) -> String {
+    match classify(err) {
+        ErrorKind::Disconnected => {
+            "Couldn't reach the authentication daemon. Make sure authforge-daemon is running."
+                .to_string()
+        }
+        ErrorKind::AccessDenied => match err {
+            zbus::Error::FDO(boxed) => match boxed.as_ref() {
+                zbus::fdo::Error::AccessDenied(msg) => msg.clone(),
+                _ => "Access denied.".to_string(),
+            },
+            _ => "Access denied.".to_string(),
+        },
+        ErrorKind::Other => err.to_string(),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn service_unknown_classifies_as_disconnected() {
+        let e = zbus::Error::FDO(Box::new(zbus::fdo::Error::ServiceUnknown(
+            "no daemon".to_string(),
+        )));
+        assert_eq!(classify(&e), ErrorKind::Disconnected);
+    }
+
+    #[test]
+    fn access_denied_classifies_as_access_denied() {
+        let e = zbus::Error::FDO(Box::new(zbus::fdo::Error::AccessDenied(
+            "polkit said no".to_string(),
+        )));
+        assert_eq!(classify(&e), ErrorKind::AccessDenied);
+    }
+
+    #[test]
+    fn access_denied_user_message_is_daemon_message_verbatim() {
+        let e = zbus::Error::FDO(Box::new(zbus::fdo::Error::AccessDenied(
+            "polkit said no".to_string(),
+        )));
+        assert_eq!(user_message(&e), "polkit said no");
+    }
+
+    #[test]
+    fn disconnected_user_message_mentions_authforge_daemon() {
+        let e = zbus::Error::FDO(Box::new(zbus::fdo::Error::ServiceUnknown(
+            "no daemon".to_string(),
+        )));
+        assert!(user_message(&e).contains("authforge-daemon"));
+    }
+}