fix: add golangci-lint config and fix all lint errors

- Add .golangci.yml with v2 config (errcheck, govet, staticcheck, misspell, etc.)
- Fix 32 errcheck issues across config, discord, ntfy, server packages
- Fix misspelling: cancelled → canceled
- Fix staticcheck: use append(slice...) instead of loop
- Fix staticcheck: remove empty error branch
- Use t.Setenv instead of os.Setenv/Unsetenv in tests
- Update CI workflow: add lint job, release tagging, ntfy notifications

internal/config/config.go

@@ -180,7 +180,7 @@ func (c *Config) watchFileSecrets(ctx context.Context) {
 		slog.Error("failed to create fsnotify watcher", "error", err)
 		return
 	}
-	defer watcher.Close()
+	defer func() { _ = watcher.Close() }()
 
 	// Watch the secrets directory
 	// Kubernetes updates secrets by changing the symlink, so watch the parent

internal/config/config_test.go

@@ -10,8 +10,7 @@ import (
 
 func TestGetEnv(t *testing.T) {
 	// Set a test env var
-	os.Setenv("TEST_CONFIG_VAR", "test_value")
-	defer os.Unsetenv("TEST_CONFIG_VAR")
+	t.Setenv("TEST_CONFIG_VAR", "test_value")
 
 	tests := []struct {
 		name       string
@@ -112,12 +111,8 @@ func TestConfig_LoadWebhookFromSecret_TrimsWhitespace(t *testing.T) {
 }
 
 func TestLoad_ParsesTopics(t *testing.T) {
-	os.Setenv("NTFY_TOPICS", "alerts, updates , notifications")
-	os.Setenv("VAULT_ENABLED", "false")
-	defer func() {
-		os.Unsetenv("NTFY_TOPICS")
-		os.Unsetenv("VAULT_ENABLED")
-	}()
+	t.Setenv("NTFY_TOPICS", "alerts, updates , notifications")
+	t.Setenv("VAULT_ENABLED", "false")
 
 	cfg, err := Load(context.Background())
 	if err != nil {
@@ -138,9 +133,9 @@ func TestLoad_ParsesTopics(t *testing.T) {
 
 func TestLoad_Defaults(t *testing.T) {
 	// Clear any existing env vars
-	os.Unsetenv("NTFY_URL")
-	os.Unsetenv("HTTP_PORT")
-	os.Unsetenv("VAULT_ENABLED")
+	t.Setenv("NTFY_URL", "")
+	t.Setenv("HTTP_PORT", "")
+	t.Setenv("VAULT_ENABLED", "")
 
 	cfg, err := Load(context.Background())
 	if err != nil {
@@ -161,8 +156,7 @@ func TestLoad_Defaults(t *testing.T) {
 }
 
 func TestLoad_VaultEnabled(t *testing.T) {
-	os.Setenv("VAULT_ENABLED", "true")
-	defer os.Unsetenv("VAULT_ENABLED")
+	t.Setenv("VAULT_ENABLED", "true")
 
 	// This will fail to init Vault (no server), but should gracefully fall back
 	cfg, err := Load(context.Background())
@@ -182,12 +176,8 @@ func TestLoad_VaultEnabled(t *testing.T) {
 
 func TestLoad_FallsBackToEnvVar(t *testing.T) {
 	webhookURL := "https://discord.com/api/webhooks/env/test"
-	os.Setenv("DISCORD_WEBHOOK_URL", webhookURL)
-	os.Setenv("VAULT_ENABLED", "false")
-	defer func() {
-		os.Unsetenv("DISCORD_WEBHOOK_URL")
-		os.Unsetenv("VAULT_ENABLED")
-	}()
+	t.Setenv("DISCORD_WEBHOOK_URL", webhookURL)
+	t.Setenv("VAULT_ENABLED", "false")
 
 	cfg, err := Load(context.Background())
 	if err != nil {

internal/config/fuzz_test.go

@@ -25,10 +25,7 @@ func FuzzParseTopics(f *testing.F) {
 			return
 		}
 
-		topics := make([]string, 0)
-		for _, topic := range splitAndTrim(input) {
-			topics = append(topics, topic)
-		}
+		topics := append([]string{}, splitAndTrim(input)...)
 
 		// Accessing results should not panic
 		_ = len(topics)

internal/discord/fuzz_test.go

@@ -116,10 +116,7 @@ func FuzzWebhookPayloadJSON(f *testing.F) {
 		}
 
 		// Marshaling should not panic
-		_, err := json.Marshal(payload)
-		if err != nil {
-			// JSON encoding errors are acceptable for invalid UTF-8
-			// but should not panic
-		}
+		// Marshaling should not panic; JSON encoding errors are acceptable for invalid UTF-8
+		_, _ = json.Marshal(payload)
 	})
 }

internal/discord/webhook.go

@@ -117,7 +117,7 @@ func (c *Client) Send(ctx context.Context, webhookURL string, msg ntfy.Message)
 	if err != nil {
 		return fmt.Errorf("send request: %w", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	// Handle rate limiting
 	if resp.StatusCode == http.StatusTooManyRequests {

internal/ntfy/client.go

@@ -61,7 +61,7 @@ func (c *Client) Subscribe(ctx context.Context, msgCh chan<- Message) {
 		err := c.connect(ctx, msgCh)
 		if err != nil {
 			if ctx.Err() != nil {
-				return // Context cancelled
+				return // Context canceled
 			}
 			slog.Error("ntfy connection failed", "error", err, "backoff", backoff)
 			time.Sleep(backoff)
@@ -90,7 +90,7 @@ func (c *Client) connect(ctx context.Context, msgCh chan<- Message) error {
 	if err != nil {
 		return fmt.Errorf("connect: %w", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	if resp.StatusCode != http.StatusOK {
 		body, _ := io.ReadAll(io.LimitReader(resp.Body, 1024))

internal/ntfy/client_test.go

@@ -80,7 +80,7 @@ func TestClient_Subscribe_ReceivesMessages(t *testing.T) {
 
 		for _, msg := range messages {
 			data, _ := json.Marshal(msg)
-			fmt.Fprintf(w, "%s\n", data)
+			_, _ = fmt.Fprintf(w, "%s\n", data)
 		}
 	}))
 	defer server.Close()
@@ -134,7 +134,7 @@ func TestClient_Subscribe_FilterEvents(t *testing.T) {
 		w.WriteHeader(http.StatusOK)
 		for _, msg := range messages {
 			data, _ := json.Marshal(msg)
-			fmt.Fprintf(w, "%s\n", data)
+			_, _ = fmt.Fprintf(w, "%s\n", data)
 		}
 	}))
 	defer server.Close()
@@ -194,7 +194,7 @@ func TestClient_Subscribe_ContextCancellation(t *testing.T) {
 func TestClient_connect_ServerError(t *testing.T) {
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusInternalServerError)
-		w.Write([]byte("internal error"))
+		_, _ = w.Write([]byte("internal error"))
 	}))
 	defer server.Close()
 
@@ -218,7 +218,7 @@ func TestClient_connect_URLConstruction(t *testing.T) {
 	defer server.Close()
 
 	client := NewClient(server.URL, []string{"alerts", "updates"})
-	client.connect(context.Background(), make(chan Message))
+	_ = client.connect(context.Background(), make(chan Message))
 
 	expected := "/alerts,updates/json"
 	if requestedURL != expected {

internal/server/server.go

@@ -71,7 +71,7 @@ func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
 	}
 
 	w.Header().Set("Content-Type", "application/json")
-	json.NewEncoder(w).Encode(status)
+	_ = json.NewEncoder(w).Encode(status)
 }
 
 func (s *Server) handleReady(w http.ResponseWriter, r *http.Request) {
@@ -89,5 +89,5 @@ func (s *Server) handleReady(w http.ResponseWriter, r *http.Request) {
 	}
 
 	w.Header().Set("Content-Type", "application/json")
-	json.NewEncoder(w).Encode(status)
+	_ = json.NewEncoder(w).Encode(status)
 }

internal/server/server_test.go

@@ -13,7 +13,7 @@ func TestServer_HealthEndpoint_StatusCodes(t *testing.T) {
 	mux := http.NewServeMux()
 	mux.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
-		w.Write([]byte(`{"status":"ok","healthy":true}`))
+		_, _ = w.Write([]byte(`{"status":"ok","healthy":true}`))
 	})
 
 	req := httptest.NewRequest(http.MethodGet, "/health", nil)
@@ -35,7 +35,7 @@ func TestServer_ReadyEndpoint_StatusCodes(t *testing.T) {
 	mux := http.NewServeMux()
 	mux.HandleFunc("/ready", func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
-		w.Write([]byte(`{"status":"ready","ready":true}`))
+		_, _ = w.Write([]byte(`{"status":"ready","ready":true}`))
 	})
 
 	req := httptest.NewRequest(http.MethodGet, "/ready", nil)
@@ -56,7 +56,7 @@ func TestServer_Shutdown(t *testing.T) {
 	}
 
 	// Start in background
-	go srv.ListenAndServe()
+	go func() { _ = srv.ListenAndServe() }()
 
 	// Give it a moment to start
 	time.Sleep(10 * time.Millisecond)
@@ -77,7 +77,7 @@ func TestServer_MetricsEndpoint(t *testing.T) {
 	mux := http.NewServeMux()
 	mux.HandleFunc("/metrics", func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusOK)
-		w.Write([]byte("# metrics here"))
+		_, _ = w.Write([]byte("# metrics here"))
 	})
 
 	req := httptest.NewRequest(http.MethodGet, "/metrics", nil)