diff --git a/backend/internal/modules/auth/handler.go b/backend/internal/modules/auth/handler.go
index 068e12e..e324b7f 100644
--- a/backend/internal/modules/auth/handler.go
+++ b/backend/internal/modules/auth/handler.go
@@ -2,10 +2,10 @@ package auth
 
 import (
 	"errors"
-	"net"
 	"net/http"
 	"strings"
 
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 
 	"github.com/gin-gonic/gin"
@@ -86,20 +86,18 @@ func (h *Handler) SendSMS(c *gin.Context) {
 		return
 	}
 
-	siteCode := strings.TrimSpace(firstNonEmpty(
-		c.GetHeader("X-Distribution-Site-Code"),
-		c.Query("distribution_site_code"),
-		c.Query("site_code"),
-		req.SiteCode,
-	))
+	siteCode := sitecode.FromRequest(c)
+	if siteCode == "" {
+		siteCode = strings.TrimSpace(req.SiteCode)
+	}
 	domain := strings.TrimSpace(firstNonEmpty(
 		c.GetHeader("X-Distribution-Domain"),
 		c.Query("distribution_domain"),
 		c.Query("domain"),
 	))
 	if siteCode == "" && domain == "" {
-		host := extractHost(c.Request.Host)
-		if host != "" && host != "localhost" && host != "127.0.0.1" && host != "::1" {
+		host := sitecode.ExtractHost(c.Request.Host)
+		if host != "" && !sitecode.IsLocalHost(host) {
 			domain = host
 		}
 	}
@@ -120,17 +118,6 @@ func firstNonEmpty(items ...string) string {
 	return ""
 }
 
-func extractHost(rawHost string) string {
-	rawHost = strings.TrimSpace(rawHost)
-	if rawHost == "" {
-		return ""
-	}
-	if host, _, err := net.SplitHostPort(rawHost); err == nil {
-		return strings.Trim(host, "[]")
-	}
-	return strings.Trim(rawHost, "[]")
-}
-
 // Login 短信验证码登录
 // @Summary      短信验证码登录
 // @Description  使用手机号和验证码登录
diff --git a/backend/internal/modules/chat/handler_common.go b/backend/internal/modules/chat/handler_common.go
index a5a79e6..7131084 100644
--- a/backend/internal/modules/chat/handler_common.go
+++ b/backend/internal/modules/chat/handler_common.go
@@ -1,25 +1,14 @@
 package chat
 
 import (
-	"strings"
-
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 
 	"github.com/gin-gonic/gin"
 )
 
 func parseSiteCode(c *gin.Context) string {
-	for _, val := range []string{
-		c.Query("distribution_site_code"),
-		c.Query("site_code"),
-		c.GetHeader("X-Distribution-Site-Code"),
-		c.GetHeader("X-Site-Code"),
-	} {
-		if trimmed := strings.TrimSpace(val); trimmed != "" {
-			return trimmed
-		}
-	}
-	return ""
+	return sitecode.FromRequest(c)
 }
 
 func (h *Handler) list(c *gin.Context, principal Principal) {
diff --git a/backend/internal/modules/chat/qrcode_ocr_test.go b/backend/internal/modules/chat/qrcode_ocr_test.go
index 2f6f36e..8a46a04 100644
--- a/backend/internal/modules/chat/qrcode_ocr_test.go
+++ b/backend/internal/modules/chat/qrcode_ocr_test.go
@@ -238,4 +238,3 @@ func TestCollectPaddleOCRJSONLTextSupportsPPOCRv6(t *testing.T) {
 		t.Fatalf("candidates = %v, want 火爆出租-778群 as first candidate", candidates)
 	}
 }
-
diff --git a/backend/internal/modules/distribution/handler.go b/backend/internal/modules/distribution/handler.go
index d07a14d..1ebb495 100644
--- a/backend/internal/modules/distribution/handler.go
+++ b/backend/internal/modules/distribution/handler.go
@@ -7,6 +7,7 @@ import (
 	"strings"
 
 	"hfb_sys/backend/internal/middleware"
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 
 	"github.com/gin-gonic/gin"
@@ -355,20 +356,13 @@ func (h *Handler) ListPublicSiteListings(c *gin.Context) {
 }
 
 func (h *Handler) GetPublicSiteInfo(c *gin.Context) {
-	code := strings.TrimSpace(c.Query("code"))
-	if code == "" {
-		code = strings.TrimSpace(c.Query("site_code"))
-	}
-	if code == "" {
-		code = strings.TrimSpace(c.GetHeader("X-Distribution-Site-Code"))
-	}
+	code := sitecode.FromQueryThenHeader(c)
 	domain := strings.TrimSpace(c.Query("domain"))
 	if code == "" && domain == "" {
-		host := c.Request.Host
-		if colon := strings.Index(host, ":"); colon != -1 {
-			host = host[:colon]
+		host := sitecode.ExtractHost(c.Request.Host)
+		if host != "" && !sitecode.IsLocalHost(host) {
+			domain = host
 		}
-		domain = host
 	}
 	info, err := h.service.GetPublicSiteInfo(c.Request.Context(), code, domain)
 	if err != nil {
@@ -382,14 +376,11 @@ func (h *Handler) GetPublicSiteInfo(c *gin.Context) {
 // 仅当域名属于系统中正常运行（active）的分销站点时返回 200，其余情况返回 404，
 // 防止任意外部未授权域名解析到该服务器刷爆 Let's Encrypt 证书申请配额。
 func (h *Handler) CheckDomain(c *gin.Context) {
-	domain := strings.ToLower(strings.TrimSpace(c.Query("domain")))
+	domain := sitecode.ExtractHost(c.Query("domain"))
 	if domain == "" {
 		c.String(http.StatusBadRequest, "domain required")
 		return
 	}
-	if colon := strings.Index(domain, ":"); colon != -1 {
-		domain = domain[:colon]
-	}
 
 	info, err := h.service.GetPublicSiteInfo(c.Request.Context(), "", domain)
 	if err != nil || info == nil || info.Status != "active" {
diff --git a/backend/internal/modules/file/storage_test.go b/backend/internal/modules/file/storage_test.go
index c78455e..30fe416 100644
--- a/backend/internal/modules/file/storage_test.go
+++ b/backend/internal/modules/file/storage_test.go
@@ -91,4 +91,3 @@ func TestNormalizeSceneListingScreenshotAndOperatingExpense(t *testing.T) {
 		t.Fatalf("normalize operating_expense scene = %q, want operating-expense", got)
 	}
 }
-
diff --git a/backend/internal/modules/listing/handler_parse.go b/backend/internal/modules/listing/handler_parse.go
index 10bb386..4b55f47 100644
--- a/backend/internal/modules/listing/handler_parse.go
+++ b/backend/internal/modules/listing/handler_parse.go
@@ -5,6 +5,7 @@ import (
 	"strings"
 
 	"hfb_sys/backend/internal/middleware"
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 
 	"github.com/gin-gonic/gin"
@@ -119,7 +120,7 @@ func parsePublicListQuery(c *gin.Context) PublicListQuery {
 		MinSecretKD:          parseOptionalFloat(c.Query("min_secret_kd")),
 		MaxSecretKD:          parseOptionalFloat(c.Query("max_secret_kd")),
 		ResourceRanges:       parseResourceRanges(c),
-		DistributionSiteCode: strings.TrimSpace(firstNonEmpty(c.GetHeader("X-Distribution-Site-Code"), c.Query("distribution_site_code"), c.Query("site_code"))),
+		DistributionSiteCode: sitecode.FromRequest(c),
 	}
 	if query.PageSize > 50 {
 		query.PageSize = 50
diff --git a/backend/internal/modules/listing/handler_public.go b/backend/internal/modules/listing/handler_public.go
index 66f5ef6..763f1a9 100644
--- a/backend/internal/modules/listing/handler_public.go
+++ b/backend/internal/modules/listing/handler_public.go
@@ -3,9 +3,9 @@ package listing
 import (
 	"net/http"
 	"strconv"
-	"strings"
 
 	filemodule "hfb_sys/backend/internal/modules/file"
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 
 	"github.com/gin-gonic/gin"
@@ -25,7 +25,7 @@ func (h *Handler) FindPublic(c *gin.Context) {
 	if !ok {
 		return
 	}
-	siteCode := strings.TrimSpace(firstNonEmpty(c.GetHeader("X-Distribution-Site-Code"), c.Query("distribution_site_code"), c.Query("site_code")))
+	siteCode := sitecode.FromRequest(c)
 	item, err := h.service.FindPublic(c.Request.Context(), id, siteCode)
 	if err != nil {
 		writeListingError(c, err)
diff --git a/backend/internal/modules/listing/handler_user.go b/backend/internal/modules/listing/handler_user.go
index 1130ea0..684cdf6 100644
--- a/backend/internal/modules/listing/handler_user.go
+++ b/backend/internal/modules/listing/handler_user.go
@@ -1,6 +1,7 @@
 package listing
 
 import (
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 	"strings"
 
@@ -18,7 +19,7 @@ func (h *Handler) Create(c *gin.Context) {
 		response.BadRequest(c, listingBindErrorMessage(err))
 		return
 	}
-	siteCode := strings.TrimSpace(c.GetHeader("X-Distribution-Site-Code"))
+	siteCode := sitecode.FromRequest(c)
 	item, err := h.service.Create(c.Request.Context(), ownerID, req, siteCode)
 	if err != nil {
 		writeListingError(c, err)
@@ -42,7 +43,7 @@ func (h *Handler) Update(c *gin.Context) {
 		response.BadRequest(c, listingBindErrorMessage(err))
 		return
 	}
-	item, err := h.service.Update(c.Request.Context(), ownerID, id, req, strings.TrimSpace(c.GetHeader("X-Distribution-Site-Code")))
+	item, err := h.service.Update(c.Request.Context(), ownerID, id, req, sitecode.FromRequest(c))
 	if err != nil {
 		writeListingError(c, err)
 		return
@@ -103,7 +104,7 @@ func (h *Handler) ListMine(c *gin.Context) {
 		response.Unauthorized(c, "缺少用户上下文")
 		return
 	}
-	siteCode := strings.TrimSpace(c.GetHeader("X-Distribution-Site-Code"))
+	siteCode := sitecode.FromRequest(c)
 	items, err := h.service.ListMine(c.Request.Context(), ownerID, siteCode)
 	if err != nil {
 		writeListingError(c, err)
diff --git a/backend/internal/modules/notification/handler.go b/backend/internal/modules/notification/handler.go
index 9b66cab..140db89 100644
--- a/backend/internal/modules/notification/handler.go
+++ b/backend/internal/modules/notification/handler.go
@@ -5,6 +5,7 @@ import (
 	"strconv"
 
 	"hfb_sys/backend/internal/middleware"
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 
 	"github.com/gin-gonic/gin"
@@ -99,17 +100,7 @@ func (h *Handler) MarkRead(c *gin.Context) {
 }
 
 func parseSiteCode(c *gin.Context) string {
-	siteCode := c.Query("distribution_site_code")
-	if siteCode == "" {
-		siteCode = c.Query("site_code")
-	}
-	if siteCode == "" {
-		siteCode = c.GetHeader("X-Distribution-Site-Code")
-	}
-	if siteCode == "" {
-		siteCode = c.GetHeader("X-Site-Code")
-	}
-	return siteCode
+	return sitecode.FromRequest(c)
 }
 
 func currentUserID(c *gin.Context) (uint64, bool) {
diff --git a/backend/internal/modules/order/handler_user.go b/backend/internal/modules/order/handler_user.go
index a2fd473..2d5738b 100644
--- a/backend/internal/modules/order/handler_user.go
+++ b/backend/internal/modules/order/handler_user.go
@@ -3,6 +3,7 @@ package order
 import (
 	"strings"
 
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 
 	"github.com/gin-gonic/gin"
@@ -20,7 +21,7 @@ func (h *Handler) Create(c *gin.Context) {
 		return
 	}
 	if strings.TrimSpace(req.DistributionSiteCode) == "" {
-		req.DistributionSiteCode = strings.TrimSpace(c.GetHeader("X-Distribution-Site-Code"))
+		req.DistributionSiteCode = sitecode.FromRequest(c)
 	}
 	item, err := h.service.Create(c.Request.Context(), userID, req)
 	if err != nil {
@@ -37,7 +38,7 @@ func (h *Handler) List(c *gin.Context) {
 		return
 	}
 	page, pageSize := parsePagination(c)
-	siteCode := strings.TrimSpace(firstNonEmpty(c.GetHeader("X-Distribution-Site-Code"), c.Query("distribution_site_code"), c.Query("site_code")))
+	siteCode := sitecode.FromRequest(c)
 	items, err := h.service.ListForUser(c.Request.Context(), userID, page, pageSize, siteCode)
 	if err != nil {
 		writeOrderError(c, err)
@@ -53,7 +54,7 @@ func (h *Handler) ListSellerHandoffs(c *gin.Context) {
 		return
 	}
 	page, pageSize := parsePagination(c)
-	siteCode := strings.TrimSpace(firstNonEmpty(c.GetHeader("X-Distribution-Site-Code"), c.Query("distribution_site_code"), c.Query("site_code")))
+	siteCode := sitecode.FromRequest(c)
 	items, err := h.service.ListSellerHandoffs(c.Request.Context(), userID, SellerHandoffQuery{
 		Page:     page,
 		PageSize: pageSize,
@@ -77,7 +78,7 @@ func (h *Handler) Detail(c *gin.Context) {
 	if !ok {
 		return
 	}
-	siteCode := strings.TrimSpace(firstNonEmpty(c.GetHeader("X-Distribution-Site-Code"), c.Query("distribution_site_code"), c.Query("site_code")))
+	siteCode := sitecode.FromRequest(c)
 	item, err := h.service.FindForUser(c.Request.Context(), userID, id, siteCode)
 	if err != nil {
 		writeOrderError(c, err)
diff --git a/backend/internal/modules/payment/repository_integration_test.go b/backend/internal/modules/payment/repository_integration_test.go
index 3d1dce2..52618b2 100644
--- a/backend/internal/modules/payment/repository_integration_test.go
+++ b/backend/internal/modules/payment/repository_integration_test.go
@@ -927,4 +927,3 @@ func TestStartPaymentRoutesToDistributionSitePaymentChannel(t *testing.T) {
 		t.Fatalf("Order B expected MerchantID=%s, got %s", defaultConfig.MerchantID, savedB.MerchantID)
 	}
 }
-
diff --git a/backend/internal/modules/wallet/handler.go b/backend/internal/modules/wallet/handler.go
index 9f9b491..f1ecbc7 100644
--- a/backend/internal/modules/wallet/handler.go
+++ b/backend/internal/modules/wallet/handler.go
@@ -3,9 +3,9 @@ package wallet
 import (
 	"errors"
 	"strconv"
-	"strings"
 
 	"hfb_sys/backend/internal/middleware"
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 
 	"github.com/gin-gonic/gin"
@@ -20,17 +20,7 @@ func NewHandler(service *Service) *Handler {
 }
 
 func parseSiteCode(c *gin.Context) string {
-	for _, val := range []string{
-		c.Query("distribution_site_code"),
-		c.Query("site_code"),
-		c.GetHeader("X-Distribution-Site-Code"),
-		c.GetHeader("X-Site-Code"),
-	} {
-		if trimmed := strings.TrimSpace(val); trimmed != "" {
-			return trimmed
-		}
-	}
-	return ""
+	return sitecode.FromRequest(c)
 }
 
 func (h *Handler) Balance(c *gin.Context) {
diff --git a/backend/internal/modules/withdrawal/handler.go b/backend/internal/modules/withdrawal/handler.go
index c3c5c6a..95f5a57 100644
--- a/backend/internal/modules/withdrawal/handler.go
+++ b/backend/internal/modules/withdrawal/handler.go
@@ -2,8 +2,8 @@ package withdrawal
 
 import (
 	"strconv"
-	"strings"
 
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 
 	"github.com/gin-gonic/gin"
@@ -18,17 +18,7 @@ func NewHandler(service *Service) *Handler {
 }
 
 func parseSiteCode(c *gin.Context) string {
-	for _, val := range []string{
-		c.Query("distribution_site_code"),
-		c.Query("site_code"),
-		c.GetHeader("X-Distribution-Site-Code"),
-		c.GetHeader("X-Site-Code"),
-	} {
-		if trimmed := strings.TrimSpace(val); trimmed != "" {
-			return trimmed
-		}
-	}
-	return ""
+	return sitecode.FromRequest(c)
 }
 
 // ========== 用户端接口 ==========
diff --git a/backend/internal/modules/withdrawal/presenter.go b/backend/internal/modules/withdrawal/presenter.go
index 979194d..34561f8 100644
--- a/backend/internal/modules/withdrawal/presenter.go
+++ b/backend/internal/modules/withdrawal/presenter.go
@@ -95,29 +95,29 @@ func (r *Repository) toDetailDTO(ctx context.Context, w model.WithdrawalRequest)
 		DistributionSiteName: siteName,
 		DistributionSiteCode: siteCode,
 		UserNickname:         user.Nickname,
-		UserPhone:          user.Phone,
-		AmountCent:         w.AmountCent,
-		FeeCent:            w.FeeCent,
-		ActualAmountCent:   w.ActualAmountCent,
-		PaymentAccountID:   w.PaymentAccountID,
-		AccountType:        w.AccountType,
-		AccountName:        w.AccountName,
-		AccountNo:          fullAccountNo,
-		BankName:           w.BankName,
-		BankBranch:         w.BankBranch,
-		CertificateURLs:    certificateURLs,
-		Status:             w.Status,
-		ReviewedBy:         w.ReviewedBy,
-		ReviewedByName:     reviewedByName,
-		ReviewedAt:         w.ReviewedAt,
-		ReviewRemark:       w.ReviewRemark,
-		PaidBy:             w.PaidBy,
-		PaidByName:         paidByName,
-		PaidAt:             w.PaidAt,
-		PaymentProofURL:    w.PaymentProofURL,
-		PaymentRemark:      w.PaymentRemark,
-		CreatedAt:          w.CreatedAt,
-		UpdatedAt:          w.UpdatedAt,
+		UserPhone:            user.Phone,
+		AmountCent:           w.AmountCent,
+		FeeCent:              w.FeeCent,
+		ActualAmountCent:     w.ActualAmountCent,
+		PaymentAccountID:     w.PaymentAccountID,
+		AccountType:          w.AccountType,
+		AccountName:          w.AccountName,
+		AccountNo:            fullAccountNo,
+		BankName:             w.BankName,
+		BankBranch:           w.BankBranch,
+		CertificateURLs:      certificateURLs,
+		Status:               w.Status,
+		ReviewedBy:           w.ReviewedBy,
+		ReviewedByName:       reviewedByName,
+		ReviewedAt:           w.ReviewedAt,
+		ReviewRemark:         w.ReviewRemark,
+		PaidBy:               w.PaidBy,
+		PaidByName:           paidByName,
+		PaidAt:               w.PaidAt,
+		PaymentProofURL:      w.PaymentProofURL,
+		PaymentRemark:        w.PaymentRemark,
+		CreatedAt:            w.CreatedAt,
+		UpdatedAt:            w.UpdatedAt,
 	}, nil
 }
 
diff --git a/backend/internal/sitecode/sitecode.go b/backend/internal/sitecode/sitecode.go
new file mode 100644
index 0000000..8690441
--- /dev/null
+++ b/backend/internal/sitecode/sitecode.go
@@ -0,0 +1,79 @@
+// Package sitecode 统一解析请求中的分销站点编码。
+//
+// 此前各业务模块（auth/order/wallet/chat/notification/withdrawal/listing/distribution）
+// 各自内联解析，优先级和 TrimSpace 处理不一致，且对旧头 X-Site-Code 的支持参差不齐。
+// 本包收敛为两个入口：
+//
+//   - FromRequest：常规业务接口使用。SPA 前端（frontend/src/shared/api/client.ts）
+//     会为每个请求统一注入 X-Distribution-Site-Code 头，因此头是权威来源；
+//     query 参数与旧头仅作为非 SPA 调用（脚本、排障）的兜底。
+//   - FromQueryThenHeader：仅用于 GET /distribution/site-info 站点探测。
+//     SPA 初始化探测新站点时会话头尚未建立，此时显式 query 参数必须压过会话头。
+package sitecode
+
+import (
+	"net"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+)
+
+// HeaderName 是前端统一注入的权威站点编码请求头。
+const HeaderName = "X-Distribution-Site-Code"
+
+// LegacyHeaderName 是历史版本使用的站点编码请求头，仅作兜底兼容。
+const LegacyHeaderName = "X-Site-Code"
+
+// FromRequest 按权威优先级解析站点编码：
+// X-Distribution-Site-Code 头 → X-Site-Code 旧头 → distribution_site_code / site_code query。
+// 所有来源均做 TrimSpace，返回空串表示主站。
+func FromRequest(c *gin.Context) string {
+	return firstNonEmpty(
+		c.GetHeader(HeaderName),
+		c.GetHeader(LegacyHeaderName),
+		c.Query("distribution_site_code"),
+		c.Query("site_code"),
+	)
+}
+
+// FromQueryThenHeader 仅用于站点探测接口（GET /distribution/site-info）：
+// 显式 query 参数优先于会话头。SPA 探测新站点时会话头里还是上一个站点的编码，
+// 必须让 query 压过它，否则从主站跳转到分站时会探测到错误站点。
+func FromQueryThenHeader(c *gin.Context) string {
+	return firstNonEmpty(
+		c.Query("code"),
+		c.Query("site_code"),
+		c.Query("distribution_site_code"),
+		c.GetHeader(HeaderName),
+		c.GetHeader(LegacyHeaderName),
+	)
+}
+
+// ExtractHost 从 HTTP Host（可能带端口、IPv6 方括号）中提取纯主机名，小写化。
+func ExtractHost(rawHost string) string {
+	rawHost = strings.TrimSpace(rawHost)
+	if rawHost == "" {
+		return ""
+	}
+	var host string
+	if h, _, err := net.SplitHostPort(rawHost); err == nil {
+		host = h
+	} else {
+		host = rawHost
+	}
+	return strings.ToLower(strings.Trim(host, "[]"))
+}
+
+// IsLocalHost 判断主机名是否属于本地开发地址（不作为站点域名解析）。
+func IsLocalHost(host string) bool {
+	return host == "localhost" || host == "127.0.0.1" || host == "::1"
+}
+
+func firstNonEmpty(values ...string) string {
+	for _, v := range values {
+		if trimmed := strings.TrimSpace(v); trimmed != "" {
+			return trimmed
+		}
+	}
+	return ""
+}
diff --git a/backend/internal/sitecode/sitecode_test.go b/backend/internal/sitecode/sitecode_test.go
new file mode 100644
index 0000000..7012eb5
--- /dev/null
+++ b/backend/internal/sitecode/sitecode_test.go
@@ -0,0 +1,100 @@
+package sitecode
+
+import (
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+)
+
+func newTestContext(method, target string, headers map[string]string) *gin.Context {
+	gin.SetMode(gin.TestMode)
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	req := httptest.NewRequest(method, target, nil)
+	for k, v := range headers {
+		req.Header.Set(k, v)
+	}
+	c.Request = req
+	return c
+}
+
+func TestFromRequest(t *testing.T) {
+	cases := []struct {
+		name   string
+		target string
+		header map[string]string
+		want   string
+	}{
+		{name: "仅头", target: "/api/listings", header: map[string]string{HeaderName: "site_a"}, want: "site_a"},
+		{name: "旧头兜底", target: "/api/wallet/balance", header: map[string]string{LegacyHeaderName: "site_b"}, want: "site_b"},
+		{name: "query兜底", target: "/api/wallet/balance?distribution_site_code=site_c", header: nil, want: "site_c"},
+		{name: "短query兜底", target: "/api/orders?site_code=site_d", header: nil, want: "site_d"},
+		{name: "头优先于query", target: "/api/orders?site_code=query_site", header: map[string]string{HeaderName: "header_site"}, want: "header_site"},
+		{name: "权威头优先于旧头", target: "/api/chats", header: map[string]string{HeaderName: "new_site", LegacyHeaderName: "old_site"}, want: "new_site"},
+		{name: "空白字符修剪", target: "/api/orders?site_code=%20%20site_e%20%20", header: nil, want: "site_e"},
+		{name: "主站为空", target: "/api/orders", header: nil, want: ""},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got := FromRequest(newTestContext("GET", tc.target, tc.header))
+			if got != tc.want {
+				t.Fatalf("FromRequest() = %q, want %q", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestFromQueryThenHeader(t *testing.T) {
+	cases := []struct {
+		name   string
+		target string
+		header map[string]string
+		want   string
+	}{
+		{name: "code参数优先", target: "/distribution/site-info?code=probe_site", header: map[string]string{HeaderName: "session_site"}, want: "probe_site"},
+		{name: "site_code参数优先", target: "/distribution/site-info?site_code=probe2", header: map[string]string{HeaderName: "session"}, want: "probe2"},
+		{name: "无query时回落头", target: "/distribution/site-info", header: map[string]string{HeaderName: "session"}, want: "session"},
+		{name: "全空", target: "/distribution/site-info", header: nil, want: ""},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got := FromQueryThenHeader(newTestContext("GET", tc.target, tc.header))
+			if got != tc.want {
+				t.Fatalf("FromQueryThenHeader() = %q, want %q", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestExtractHost(t *testing.T) {
+	cases := []struct {
+		raw  string
+		want string
+	}{
+		{raw: "shop.example.com:8080", want: "shop.example.com"},
+		{raw: "shop.example.com", want: "shop.example.com"},
+		{raw: "Shop.Example.COM", want: "shop.example.com"},
+		{raw: "[::1]:5189", want: "::1"},
+		{raw: "  shop.example.com  ", want: "shop.example.com"},
+		{raw: "", want: ""},
+	}
+	for _, tc := range cases {
+		if got := ExtractHost(tc.raw); got != tc.want {
+			t.Errorf("ExtractHost(%q) = %q, want %q", tc.raw, got, tc.want)
+		}
+	}
+}
+
+func TestIsLocalHost(t *testing.T) {
+	for _, local := range []string{"localhost", "127.0.0.1", "::1"} {
+		if !IsLocalHost(local) {
+			t.Errorf("IsLocalHost(%q) 应为 true", local)
+		}
+	}
+	for _, remote := range []string{"shop.example.com", "0.0.0.0", ""} {
+		if IsLocalHost(remote) {
+			t.Errorf("IsLocalHost(%q) 应为 false", remote)
+		}
+	}
+}