feat: implement comprehensive configuration validation and integrate into store loading and server initialization.

internal/server/router.go

@@ -3,6 +3,7 @@ package server
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"net/http"
 	"strings"
 	"time"
@@ -29,8 +30,11 @@ type App struct {
 	Router   http.Handler
 }
 
-func NewApp() *App {
-	store := config.LoadStore()
+func NewApp() (*App, error) {
+	store, err := config.LoadStoreWithError()
+	if err != nil {
+		return nil, fmt.Errorf("load config: %w", err)
+	}
 	pool := account.NewPool(store)
 	var dsClient *deepseek.Client
 	resolver := auth.NewResolver(store, pool, func(ctx context.Context, acc config.Account) (string, error) {
@@ -85,7 +89,7 @@ func NewApp() *App {
 		http.NotFound(w, req)
 	})
 
-	return &App{Store: store, Pool: pool, Resolver: resolver, DS: dsClient, Router: r}
+	return &App{Store: store, Pool: pool, Resolver: resolver, DS: dsClient, Router: r}, nil
 }
 
 func timeout(d time.Duration) func(http.Handler) http.Handler {

internal/server/router_health_test.go

@@ -7,7 +7,13 @@ import (
 )
 
 func TestHealthEndpointsSupportHEAD(t *testing.T) {
-	app := NewApp()
+	t.Setenv("DS2API_CONFIG_JSON", `{"keys":["k1"],"accounts":[{"email":"u@example.com","password":"p"}]}`)
+	t.Setenv("DS2API_ENV_WRITEBACK", "0")
+
+	app, err := NewApp()
+	if err != nil {
+		t.Fatalf("NewApp() error: %v", err)
+	}
 
 	for _, path := range []string{"/healthz", "/readyz"} {
 		req := httptest.NewRequest(http.MethodHead, path, nil)