improvements jan2025 (#6)

* feat(controller): add lazy watcher, improve resource usage and add pattern validation

- [x] Add cache sync health check for readiness probe verification
- [x] Create namespace lister with API reader support for fresh label queries
- [x] Add pattern validation with warning logs for invalid glob patterns
- [x] Implement lazy watcher initialization mode to scan for active resources
- [x] Add requeue delay to namespace reconciler for cache settlement
- [x] Replace custom containsString with slices.Contains from stdlib
- [x] Add structured logging context to reconcilers (kind, group, version)
- [x] Improve error variable naming for clarity in nested conditions
- [x] Add nil-safe label access in namespace reconciler setup
- [x] Add APIReader to namespace and source reconcilers for fresh data
- [x] Improve type assertions with proper error handling in mirror operations
- [x] Reorder struct fields for consistency and readability
- [x] Add comprehensive pattern validation tests and validation API

* feat(controller): add lazy watcher, improve resource usage and add pattern validation

- [x] Add circuit breaker for reconciliation failure tracking and prevention
- [x] Implement granular registration state tracking (not-registered, source-only, fully-registered)
- [x] Add lazy controller initialization for active resource types only
- [x] Consolidate namespace listing into single API call for efficiency
- [x] Add mirror creation verification to catch webhook rejections
- [x] Implement high-cardinality resource detection and warnings
- [x] Add source deletion check in mirror reconciler to prevent races
- [x] Preserve transformation annotations on errors in mirror reconciliation
- [x] Expand constants documentation with labels vs annotations design rationale
- [x] Add comprehensive test coverage for circuit breaker and registration states
- [x] Add mutation-safety tests for hash computation

* fixup! feat(controller): add lazy watcher, improve resource usage and add pattern validation

pkg/discovery/discovery_test.go

@@ -86,3 +86,33 @@ func TestIsDeniedResourceType(t *testing.T) {
 		})
 	}
 }
+
+func TestIsHighCardinalityResource(t *testing.T) {
+	tests := []struct {
+		name string
+		kind string
+		want bool
+	}{
+		// High cardinality resources (should warn)
+		{name: "ServiceAccount", kind: "ServiceAccount", want: true},
+		{name: "Role", kind: "Role", want: true},
+		{name: "RoleBinding", kind: "RoleBinding", want: true},
+		{name: "NetworkPolicy", kind: "NetworkPolicy", want: true},
+		{name: "ServiceMonitor", kind: "ServiceMonitor", want: true},
+		{name: "VirtualService", kind: "VirtualService", want: true},
+
+		// Not high cardinality (no warning needed)
+		{name: "Secret", kind: "Secret", want: false},
+		{name: "ConfigMap", kind: "ConfigMap", want: false},
+		{name: "Service", kind: "Service", want: false},
+		{name: "Deployment", kind: "Deployment", want: false},
+		{name: "Middleware", kind: "Middleware", want: false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := isHighCardinalityResource(tt.kind)
+			assert.Equal(t, tt.want, got, "isHighCardinalityResource(%s) = %v, want %v", tt.kind, got, tt.want)
+		})
+	}
+}