test(bare): add comprehensive tests for GitBare functionality

- Add test_from_header_valid to verify valid repository header parsing
- Add test_from_header_empty_path to handle empty path scenarios
- Add test_from_header_relative_storage_path to validate absolute paths
- Add test_from_header_relative_path_without_storage for missing storage
- Add test_from_header_nonexistent_repo to check repo existence
- Add test_from_header_path_traversal to prevent directory traversal
- Add test_from_header_not_a_directory for file instead of directory
- Add test_from_header_dir_without_head to verify bare repository format
- Add test_object_format to validate object format detection
- Add test_oid_to_pb to verify OID conversion functionality
- Add test_oid_to_pb_invalid_hex to handle invalid hex input gracefully

test(error): add comprehensive error handling tests

- Add test_error_display_variants to verify error message formatting
- Add test_error_is_debug to

tests/refs_test.rs

@@ -0,0 +1,64 @@
+mod common;
+
+fn hdr() -> gitks::pb::RepositoryHeader {
+    gitks::pb::RepositoryHeader {
+        relative_path: "test-repo".into(),
+        ..Default::default()
+    }
+}
+
+#[tokio::test]
+async fn test_list_refs_via_service() {
+    let (dir, _gb) = common::setup_bare_repo();
+    let svc = common::setup_service(dir.path());
+
+    // list_refs is called internally by advertise_refs
+    // We test it indirectly through the service
+    use gitks::pb::pack_service_server::PackService;
+    let result = svc
+        .advertise_refs(tonic::Request::new(gitks::pb::AdvertiseRefsRequest {
+            repository: Some(hdr()),
+            protocol: None,
+            service: String::new(),
+        }))
+        .await
+        .unwrap()
+        .into_inner();
+
+    assert!(!result.references.is_empty(), "should have refs");
+    let names: Vec<&str> = result.references.iter().map(|r| r.name.as_str()).collect();
+    assert!(
+        names.iter().any(|n| n.contains("refs/heads/main")),
+        "should have main branch, got: {:?}",
+        names
+    );
+    assert!(
+        names.iter().any(|n| n.contains("refs/heads/feature")),
+        "should have feature branch, got: {:?}",
+        names
+    );
+    assert!(
+        names.iter().any(|n| n.contains("refs/tags/v0.1.0")),
+        "should have tag, got: {:?}",
+        names
+    );
+}
+
+#[test]
+fn test_list_refs_direct() {
+    let (_dir, gb) = common::setup_bare_repo();
+    let refs = gb.list_refs().expect("list_refs");
+
+    assert!(!refs.is_empty());
+    let names: Vec<&str> = refs.iter().map(|r| r.name.as_str()).collect();
+    assert!(names.iter().any(|n| n.contains("refs/heads/main")));
+    assert!(names.iter().any(|n| n.contains("refs/heads/feature")));
+    assert!(names.iter().any(|n| n.contains("refs/tags/v0.1.0")));
+
+    // Each ref should have a valid target OID
+    for r in &refs {
+        let oid = r.target_oid.as_ref().expect("ref should have target_oid");
+        assert!(!oid.hex.is_empty(), "OID hex should not be empty");
+        assert_eq!(oid.hex.len(), 40, "SHA-1 hex should be 40 chars");
+    }
+}