feat(api): add /health endpoint with Docker healthchecks

Allow Docker to distinguish a running container from one actually
serving traffic by adding a /health endpoint that pings the database.
Returns 200 when healthy, 503 when the DB connection is lost.

Add HEALTHCHECK to Dockerfile and healthcheck config to the server
service in docker-compose.yml. Also add start_period to the existing
db healthcheck for consistency.

server/api/api_server.go

@@ -26,6 +26,7 @@ type Config struct {
 type APIServer struct {
 	sync.Mutex
 	logger         *zap.Logger
+	db             *sqlx.DB
 	erupeConfig    *cfg.Config
 	userRepo       APIUserRepo
 	charRepo       APICharacterRepo
@@ -38,6 +39,7 @@ type APIServer struct {
 func NewAPIServer(config *Config) *APIServer {
 	s := &APIServer{
 		logger:      config.Logger,
+		db:          config.DB,
 		erupeConfig: config.ErupeConfig,
 		httpServer:  &http.Server{},
 	}
@@ -61,6 +63,7 @@ func (s *APIServer) Start() error {
 	r.HandleFunc("/character/export", s.ExportSave)
 	r.HandleFunc("/api/ss/bbs/upload.php", s.ScreenShot)
 	r.HandleFunc("/api/ss/bbs/{id}", s.ScreenShotGet)
+	r.HandleFunc("/health", s.Health)
 	r.HandleFunc("/version", s.Version)
 	handler := handlers.CORS(handlers.AllowedHeaders([]string{"Content-Type"}))(r)
 	s.httpServer.Handler = handlers.LoggingHandler(os.Stdout, handler)

server/api/endpoints.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"context"
 	"database/sql"
 	"encoding/json"
 	"encoding/xml"
@@ -443,3 +444,30 @@ func (s *APIServer) ScreenShot(w http.ResponseWriter, r *http.Request) {
 
 	writeResult("200")
 }
+
+// Health handles GET /health, returning the server's health status.
+// It pings the database to verify connectivity.
+func (s *APIServer) Health(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	if s.db == nil {
+		w.WriteHeader(http.StatusServiceUnavailable)
+		_ = json.NewEncoder(w).Encode(map[string]string{
+			"status": "unhealthy",
+			"error":  "database not configured",
+		})
+		return
+	}
+	ctx, cancel := context.WithTimeout(r.Context(), 3*time.Second)
+	defer cancel()
+	if err := s.db.PingContext(ctx); err != nil {
+		w.WriteHeader(http.StatusServiceUnavailable)
+		_ = json.NewEncoder(w).Encode(map[string]string{
+			"status": "unhealthy",
+			"error":  err.Error(),
+		})
+		return
+	}
+	_ = json.NewEncoder(w).Encode(map[string]string{
+		"status": "ok",
+	})
+}

server/api/endpoints_test.go

@@ -572,6 +572,44 @@ func TestNewAuthDataTimestamps(t *testing.T) {
 	}
 }
 
+// TestHealthEndpointNoDB tests the /health endpoint when no database is configured.
+func TestHealthEndpointNoDB(t *testing.T) {
+	logger := NewTestLogger(t)
+	defer func() { _ = logger.Sync() }()
+
+	server := &APIServer{
+		logger:      logger,
+		erupeConfig: NewTestConfig(),
+		db:          nil,
+	}
+
+	req := httptest.NewRequest("GET", "/health", nil)
+	recorder := httptest.NewRecorder()
+
+	server.Health(recorder, req)
+
+	if recorder.Code != http.StatusServiceUnavailable {
+		t.Errorf("Expected status %d, got %d", http.StatusServiceUnavailable, recorder.Code)
+	}
+
+	if contentType := recorder.Header().Get("Content-Type"); contentType != "application/json" {
+		t.Errorf("Content-Type = %v, want application/json", contentType)
+	}
+
+	var resp map[string]string
+	if err := json.NewDecoder(recorder.Body).Decode(&resp); err != nil {
+		t.Fatalf("Failed to decode response: %v", err)
+	}
+
+	if resp["status"] != "unhealthy" {
+		t.Errorf("status = %q, want %q", resp["status"], "unhealthy")
+	}
+
+	if resp["error"] != "database not configured" {
+		t.Errorf("error = %q, want %q", resp["error"], "database not configured")
+	}
+}
+
 // BenchmarkLauncherEndpoint benchmarks the launcher endpoint
 func BenchmarkLauncherEndpoint(b *testing.B) {
 	logger, _ := zap.NewDevelopment()