feat(core): refactor linters config and improve code quality (#119)

- [x] Reorganize golangci-lint configuration with documented disable reasons
- [x] Simplify errcheck and revive linter rules with targeted exclusions
- [x] Pre-compile regex patterns in input_validation.go for performance
- [x] Fix type assertions in memory_shard.go and resp.go with safety checks
- [x] Replace string comparison with EqualFold for case-insensitive matching
- [x] Fix loop variable captures in jwk.go and logout.go
- [x] Change high goroutine log level from Info to Debug in autocleanup.go
- [x] Replace deprecated "cancelled" spelling with "canceled" throughout
- [x] Add nolint annotations for intentional unused parameters
- [x] Improve comment formatting for deprecated functions
- [x] Fix comment spelling: "marshalling" → "marshaling"
- [x] Refactor provider warnings formatting in internal/providers/warnings.go
- [x] Simplify metrics summary building in internal/recovery/metrics.go
- [x] Pre-allocate slice in error_recovery.go GetDegradedServices
- [x] Refactor context cancellation checks in redis.go

internal/cache/backends/memory_shard.go

@@ -241,9 +241,11 @@ func (s *cacheShard) evictLRULocked() bool {
 
 	element := s.lruList.Back()
 	if element != nil {
-		item := element.Value.(*memoryCacheItem)
-		s.deleteItemLocked(item)
-		return true
+		item, ok := element.Value.(*memoryCacheItem)
+		if ok {
+			s.deleteItemLocked(item)
+			return true
+		}
 	}
 	return false
 }
@@ -267,8 +269,10 @@ func (s *cacheShard) getOldestAccessTime() time.Time {
 
 	element := s.lruList.Back()
 	if element != nil {
-		item := element.Value.(*memoryCacheItem)
-		return item.accessedAt
+		item, ok := element.Value.(*memoryCacheItem)
+		if ok {
+			return item.accessedAt
+		}
 	}
 	return time.Time{}
 }

internal/cache/backends/redis.go

@@ -345,7 +345,7 @@ func (r *RedisBackend) prefixKey(key string) string {
 
 // executeWithRetry executes a Redis operation with exponential backoff retry logic.
 // It checks context cancellation at multiple points to ensure fast abort when the
-// caller's context is cancelled (e.g., due to request timeout).
+// caller's context is canceled (e.g., due to request timeout).
 func (r *RedisBackend) executeWithRetry(ctx context.Context, operation func(*RedisConn) error) error {
 	maxRetries := 3
 	baseDelay := 50 * time.Millisecond // Reduced from 100ms to fail faster
@@ -377,7 +377,7 @@ func (r *RedisBackend) executeWithRetry(ctx context.Context, operation func(*Red
 		err = operation(conn)
 		r.pool.Put(conn)
 
-		// Check context after operation - if cancelled, don't bother retrying
+		// Check context after operation - if canceled, don't bother retrying
 		if ctx.Err() != nil {
 			return ctx.Err()
 		}

internal/cache/backends/redis_pool_test.go

@@ -201,7 +201,7 @@ func TestConnectionPool_ContextCancellation(t *testing.T) {
 	conn, err := pool.Get(context.Background())
 	require.NoError(t, err)
 
-	// Try to get another with cancelled context
+	// Try to get another with canceled context
 	ctx, cancel := context.WithCancel(context.Background())
 	cancel() // Cancel immediately
 

internal/cache/backends/resp.go

@@ -44,7 +44,7 @@ type RESPWriter struct {
 
 // NewRESPWriter creates a new RESP writer from the pool (memory optimized)
 func NewRESPWriter(w io.Writer) *RESPWriter {
-	writer := writerPool.Get().(*RESPWriter)
+	writer, _ := writerPool.Get().(*RESPWriter)
 	writer.w = w
 	return writer
 }
@@ -80,7 +80,7 @@ type RESPReader struct {
 
 // NewRESPReader creates a new RESP reader from the pool (memory optimized)
 func NewRESPReader(r io.Reader) *RESPReader {
-	reader := readerPool.Get().(*RESPReader)
+	reader, _ := readerPool.Get().(*RESPReader)
 	reader.r.Reset(r)
 	return reader
 }

internal/cache/backends/singleflight.go

@@ -87,7 +87,7 @@ func (s *SingleflightCache) GetOrFetch(ctx context.Context, key string, fetcher
 	// If successful, store in cache
 	if call.err == nil && call.val != nil {
 		// Use a background context for cache storage to ensure it completes
-		// even if the original context is cancelled
+		// even if the original context is canceled
 		storeCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 		_ = s.backend.Set(storeCtx, key, call.val, call.ttl)
 		cancel()

internal/cache/manager.go

@@ -232,7 +232,7 @@ func (m *Manager) Close() error {
 
 	var firstErr error
 
-	if err := m.tokenCache.Close(); err != nil && firstErr == nil {
+	if err := m.tokenCache.Close(); err != nil {
 		firstErr = err
 	}
 	if err := m.metadataCache.Close(); err != nil && firstErr == nil {

internal/cleanup/workers.go

@@ -397,7 +397,7 @@ func (wp *WorkerPool) Submit(task func()) error {
 }
 
 // worker is the main worker routine
-func (wp *WorkerPool) worker(id int) {
+func (wp *WorkerPool) worker(_ int) {
 	defer wp.workerWg.Done()
 
 	for {

internal/features/flags.go

@@ -173,7 +173,7 @@ func (m *FeatureManager) LoadFromEnv() {
 	for name, flag := range flags {
 		envVar := "FEATURE_" + name
 		if value := os.Getenv(envVar); value != "" {
-			enabled := strings.ToLower(value) == "true" || value == "1"
+			enabled := strings.EqualFold(value, "true") || value == "1"
 			flag.enabled.Store(enabled)
 		}
 	}

internal/providers/aws_cognito.go

@@ -40,7 +40,7 @@ func (p *AWSCognitoProvider) BuildAuthParams(baseParams url.Values, scopes []str
 	// Remove offline_access scope as Cognito doesn't use it (case-insensitive)
 	var filteredScopes []string
 	for _, scope := range scopes {
-		if strings.ToLower(scope) != ScopeOfflineAccess {
+		if !strings.EqualFold(scope, ScopeOfflineAccess) {
 			filteredScopes = append(filteredScopes, scope)
 		}
 	}

internal/providers/warnings.go

@@ -18,16 +18,17 @@ func GetProviderWarnings(providerType ProviderType) []ProviderWarning {
 
 	switch providerType {
 	case ProviderTypeGitHub:
-		warnings = append(warnings, ProviderWarning{
-			ProviderType: ProviderTypeGitHub,
-			Level:        "warning",
-			Message:      "GitHub uses OAuth 2.0, not OpenID Connect. ID tokens are not available. Use access tokens for API calls only.",
-		})
-		warnings = append(warnings, ProviderWarning{
-			ProviderType: ProviderTypeGitHub,
-			Level:        "info",
-			Message:      "GitHub OAuth apps do not support refresh tokens. Users will need to re-authenticate when tokens expire.",
-		})
+		warnings = append(warnings,
+			ProviderWarning{
+				ProviderType: ProviderTypeGitHub,
+				Level:        "warning",
+				Message:      "GitHub uses OAuth 2.0, not OpenID Connect. ID tokens are not available. Use access tokens for API calls only.",
+			},
+			ProviderWarning{
+				ProviderType: ProviderTypeGitHub,
+				Level:        "info",
+				Message:      "GitHub OAuth apps do not support refresh tokens. Users will need to re-authenticate when tokens expire.",
+			})
 
 	case ProviderTypeAuth0:
 		warnings = append(warnings, ProviderWarning{

internal/recovery/metrics.go

@@ -116,7 +116,7 @@ func (re *RetryExecutor) ExecuteWithContext(ctx context.Context, fn func() error
 			// Continue to next attempt
 		case <-ctx.Done():
 			re.RecordFailure()
-			return fmt.Errorf("retry cancelled: %w", ctx.Err())
+			return fmt.Errorf("retry canceled: %w", ctx.Err())
 		}
 	}
 
@@ -301,7 +301,7 @@ func (rm *RecoveryMetrics) GetAllMetrics() map[string]interface{} {
 		}
 	}
 
-	allMetrics["summary"] = map[string]interface{}{
+	summary := map[string]interface{}{
 		"totalMechanisms": len(rm.mechanisms),
 		"totalRequests":   totalRequests,
 		"totalSuccesses":  totalSuccesses,
@@ -310,8 +310,9 @@ func (rm *RecoveryMetrics) GetAllMetrics() map[string]interface{} {
 
 	if totalRequests > 0 {
 		successRate := float64(totalSuccesses) / float64(totalRequests) * 100
-		allMetrics["summary"].(map[string]interface{})["overallSuccessRate"] = fmt.Sprintf("%.2f%%", successRate)
+		summary["overallSuccessRate"] = fmt.Sprintf("%.2f%%", successRate)
 	}
+	allMetrics["summary"] = summary
 
 	return allMetrics
 }

internal/recovery/metrics_test.go

@@ -223,7 +223,7 @@ func TestRetryExecutor_ExecuteWithContext_ContextCancelled(t *testing.T) {
 	wg.Wait()
 
 	if execErr == nil {
-		t.Error("Expected error when context is cancelled")
+		t.Error("Expected error when context is canceled")
 	}
 }
 
@@ -240,7 +240,7 @@ func TestRetryExecutor_ExecuteWithContext_ContextCancelledBeforeStart(t *testing
 	})
 
 	if err == nil {
-		t.Error("Expected error when context is already cancelled")
+		t.Error("Expected error when context is already canceled")
 	}
 }
 
@@ -282,7 +282,7 @@ func TestRetryExecutor_isRetryableError(t *testing.T) {
 		{name: "timeout", err: errors.New("TIMEOUT"), expected: true}, // case insensitive
 		{name: "EOF", err: errors.New("EOF"), expected: false},
 		{name: "random error", err: errors.New("something else"), expected: false},
-		{name: "context cancelled", err: context.Canceled, expected: false},
+		{name: "context canceled", err: context.Canceled, expected: false},
 		{name: "context deadline exceeded", err: context.DeadlineExceeded, expected: false},
 	}