fix(health): report readiness instead of static 200

The health endpoint returned 200 unconditionally from before dependencies were ready and never reflected MongoDB state. Handler now takes a readiness check; the endpoint returns 503 while starting or when MongoDB is unreachable and 200 only when ready.

internal/health/server.go

@@ -13,19 +13,35 @@ const (
 	Path    = "/healthz"
 )
 
-func Handler() http.Handler {
+// Check reports whether the bot is ready to serve. It returns nil when healthy
+// and an error describing why not otherwise. A nil Check is always healthy.
+type Check func(ctx context.Context) error
+
+// Handler serves the health endpoint. It returns 200 only when check passes,
+// and 503 while the bot is still starting or a dependency is unreachable, so an
+// orchestrator probe reflects real readiness instead of a static 200.
+func Handler(check Check) http.Handler {
 	mux := http.NewServeMux()
-	mux.HandleFunc(Path, func(w http.ResponseWriter, _ *http.Request) {
+	mux.HandleFunc(Path, func(w http.ResponseWriter, r *http.Request) {
+		if check != nil {
+			ctx, cancel := context.WithTimeout(r.Context(), 2*time.Second)
+			defer cancel()
+			if err := check(ctx); err != nil {
+				w.WriteHeader(http.StatusServiceUnavailable)
+				_, _ = w.Write([]byte("unavailable\n"))
+				return
+			}
+		}
 		w.WriteHeader(http.StatusOK)
 		_, _ = w.Write([]byte("ok\n"))
 	})
 	return mux
 }
 
-func Run(ctx context.Context, logger *slog.Logger) {
+func Run(ctx context.Context, logger *slog.Logger, check Check) {
 	server := &http.Server{
 		Addr:              Address,
-		Handler:           Handler(),
+		Handler:           Handler(check),
 		ReadHeaderTimeout: 3 * time.Second,
 	}
 

internal/health/server_test.go

@@ -1,16 +1,18 @@
 package health
 
 import (
+	"context"
+	"errors"
 	"net/http"
 	"net/http/httptest"
 	"testing"
 )
 
-func TestHandlerReturnsOK(t *testing.T) {
+func TestHandlerReturnsOKWhenCheckPasses(t *testing.T) {
 	req := httptest.NewRequest(http.MethodGet, Path, nil)
 	res := httptest.NewRecorder()
 
-	Handler().ServeHTTP(res, req)
+	Handler(func(context.Context) error { return nil }).ServeHTTP(res, req)
 
 	if res.Code != http.StatusOK {
 		t.Fatalf("status = %d, want %d", res.Code, http.StatusOK)
@@ -19,3 +21,25 @@ func TestHandlerReturnsOK(t *testing.T) {
 		t.Fatalf("body = %q, want ok", res.Body.String())
 	}
 }
+
+func TestHandlerNilCheckIsHealthy(t *testing.T) {
+	req := httptest.NewRequest(http.MethodGet, Path, nil)
+	res := httptest.NewRecorder()
+
+	Handler(nil).ServeHTTP(res, req)
+
+	if res.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d", res.Code, http.StatusOK)
+	}
+}
+
+func TestHandlerReturnsUnavailableWhenCheckFails(t *testing.T) {
+	req := httptest.NewRequest(http.MethodGet, Path, nil)
+	res := httptest.NewRecorder()
+
+	Handler(func(context.Context) error { return errors.New("not ready") }).ServeHTTP(res, req)
+
+	if res.Code != http.StatusServiceUnavailable {
+		t.Fatalf("status = %d, want %d", res.Code, http.StatusServiceUnavailable)
+	}
+}