HH-442: isolate runtime processes and harden shutdown (#90)

* HH-442: isolate runtime processes and harden shutdown

* HH-442: harden worker shutdown races

* HH-442: gate dependency shutdown on active handlers

---------

Co-authored-by: Rogee <rogee@ipao.vip>

backend/internal/handler/handler_test.go

@@ -1,7 +1,9 @@
 package handler
 
 import (
+	"context"
 	"encoding/json"
+	"errors"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -93,6 +95,49 @@ func TestReadyHandler_Ready(t *testing.T) {
 	assert.True(t, resp["ready"].(bool))
 }
 
+func TestReadyHandler_RequiredDependencyFailure(t *testing.T) {
+	db := newTestDB(t)
+	router := gin.New()
+	router.GET("/ready", ReadyHandler(db, DependencyCheck{Name: "redis", Check: func(context.Context) error {
+		return errors.New("connection refused")
+	}}))
+
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, httptest.NewRequest(http.MethodGet, "/ready", nil))
+	assert.Equal(t, http.StatusServiceUnavailable, w.Code)
+	assert.JSONEq(t, `{"ready":false,"checks":{"database":"healthy","redis":"unhealthy: connection refused"}}`, w.Body.String())
+}
+
+func TestDatabaseOutageFailsReadinessButNotLiveness(t *testing.T) {
+	db := newTestDB(t)
+	sqlDB, err := db.DB()
+	require.NoError(t, err)
+	require.NoError(t, sqlDB.Close())
+	router := gin.New()
+	router.GET("/ready", ReadyHandler(db))
+	router.GET("/live", LiveHandler())
+
+	ready := httptest.NewRecorder()
+	router.ServeHTTP(ready, httptest.NewRequest(http.MethodGet, "/ready", nil))
+	assert.Equal(t, http.StatusServiceUnavailable, ready.Code)
+	live := httptest.NewRecorder()
+	router.ServeHTTP(live, httptest.NewRequest(http.MethodGet, "/live", nil))
+	assert.Equal(t, http.StatusOK, live.Code)
+}
+
+func TestHealthHandler_SelectedDependency(t *testing.T) {
+	db := newTestDB(t)
+	router := gin.New()
+	router.GET("/health", HealthHandler(db, time.Now(), "test", DependencyCheck{Name: "redis", Check: func(context.Context) error { return nil }}))
+
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, httptest.NewRequest(http.MethodGet, "/health?check=redis", nil))
+	assert.Equal(t, http.StatusOK, w.Code)
+	var response HealthResponse
+	require.NoError(t, json.Unmarshal(w.Body.Bytes(), &response))
+	assert.Equal(t, map[string]string{"redis": "healthy"}, response.Checks)
+}
+
 func TestReadyHandler_NilDB_NotReady(t *testing.T) {
 	// ReadyHandler does not handle nil DB (panics on db.DB()).
 	t.Skip("ReadyHandler panics on nil DB; nil DB is not a valid runtime state")
@@ -144,6 +189,23 @@ func TestPrometheusHandler(t *testing.T) {
 	assert.Contains(t, body, "# TYPE")
 }
 
+func TestHTTPMetricsRecordsRequestsErrorsAndLatency(t *testing.T) {
+	metrics := NewHTTPMetrics(time.Now())
+	router := gin.New()
+	router.Use(metrics.Middleware())
+	router.GET("/items/:id", func(c *gin.Context) { c.Status(http.StatusInternalServerError) })
+	router.GET("/metrics", metrics.Handler())
+
+	router.ServeHTTP(httptest.NewRecorder(), httptest.NewRequest(http.MethodGet, "/items/42", nil))
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, httptest.NewRequest(http.MethodGet, "/metrics", nil))
+
+	body := w.Body.String()
+	assert.Contains(t, body, `http_requests_total{method="GET",route="/items/:id",status="500"} 1`)
+	assert.Contains(t, body, `http_request_errors_total{method="GET",route="/items/:id",status="500"} 1`)
+	assert.Contains(t, body, `http_request_duration_seconds_count{method="GET",route="/items/:id",status="500"} 1`)
+}
+
 func TestFormatGauge(t *testing.T) {
 	result := formatGauge("test_metric", 42)
 	assert.Equal(t, "test_metric 42", result)