autoresearch iter 2: compare error sentinels with errors.Is

Five sites used == against sentinels (redis.Nil, ingest.ErrForbidden,
errs.ErrDatabaseUninitialized). The neighbouring not-found checks already
went through errors.Is helpers, so a wrapped error would silently downgrade
a 403 to a 400 and a 500 to a 400.

backend/plugins/domain/admin/handler/db.go

@@ -10,6 +10,7 @@ import (
 	"Wavelet/plugins/domain/admin/errs"
 	"Wavelet/plugins/domain/admin/model"
 	"Wavelet/plugins/domain/admin/service"
+	"errors"
 	"fmt"
 	"net/http"
 	"strings"
@@ -109,7 +110,7 @@ func ExecuteSQL(c *gin.Context) {
 
 	resp, err := service.ExecuteCustomSQL(c.Request.Context(), trimmedSQL)
 	if err != nil {
-		if err == errs.ErrDatabaseUninitialized {
+		if errors.Is(err, errs.ErrDatabaseUninitialized) {
 			response.AbortInternal(c, err.Error())
 			return
 		}

backend/plugins/domain/cap/pow/store.go

@@ -5,6 +5,7 @@ package pow
 
 import (
 	"context"
+	"errors"
 	"sync"
 	"time"
 
@@ -149,7 +150,7 @@ func NewRedisStore(client redis.UniversalClient) *RedisStore {
 // Get 从 RedisStore 获取指定 key 的值
 func (s *RedisStore) Get(ctx context.Context, key string) (string, bool, error) {
 	val, err := s.client.Get(ctx, key).Result()
-	if err == redis.Nil {
+	if errors.Is(err, redis.Nil) {
 		return "", false, nil
 	}
 	if err != nil {
@@ -176,7 +177,7 @@ func (s *RedisStore) SetNX(ctx context.Context, key, val string, ttl time.Durati
 // GetAndDelete wraps Redis GETDEL (available since Redis 6.2).
 func (s *RedisStore) GetAndDelete(ctx context.Context, key string) (string, bool, error) {
 	val, err := s.client.GetDel(ctx, key).Result()
-	if err == redis.Nil {
+	if errors.Is(err, redis.Nil) {
 		return "", false, nil
 	}
 	if err != nil {

backend/plugins/domain/upload/handler/file_management.go

@@ -11,6 +11,7 @@ import (
 	"Wavelet/plugins/domain/upload/models"
 	"Wavelet/plugins/domain/upload/repository"
 	"Wavelet/plugins/domain/upload/shared"
+	"errors"
 	"net/http"
 	"strconv"
 
@@ -233,7 +234,7 @@ func DeleteMyFile(c *gin.Context) {
 			response.AbortNotFound(c, shared.ErrFileRecordNotFound)
 			return
 		}
-		if err == ingest.ErrForbidden {
+		if errors.Is(err, ingest.ErrForbidden) {
 			response.AbortForbidden(c, shared.ErrOperationForbidden)
 			return
 		}
@@ -287,7 +288,7 @@ func UpdateMyFile(c *gin.Context) {
 			response.AbortNotFound(c, shared.ErrFileRecordNotFound)
 			return
 		}
-		if err == ingest.ErrForbidden {
+		if errors.Is(err, ingest.ErrForbidden) {
 			response.AbortForbidden(c, shared.ErrOperationForbidden)
 			return
 		}