fix(openresty): preserve origin error status on custom error pages

Remove error_page '=' form that adopted the internal URI status (often 200)
and left ngx.status as 0. Resolve the original code from $status/upstream
and set ngx.status before rendering the HTML body.

docs/changelog/index.md

@@ -29,6 +29,7 @@ sidebar: false
 
 ### 修复
 
+- 修复源站错误页在边缘返回 HTTP 200、页面状态码显示异常（如 0）的问题：错误响应现在正确透传上游状态码，并在页面中展示真实状态码。
 - 修复 Agent 在配置已对齐但磁盘校验和不一致时，Pages 等对账成功后仍保留 `LastError` 的问题，避免偶发网络失败被健康事件长期显示为「活动中」且无法自动恢复。
 
 ### 改进

pkg/render/openresty/origin_error_page.go

@@ -135,6 +135,11 @@ func renderOriginErrorPageIntercept(cfg ConfigSnapshot) string {
 
 // renderOriginErrorPageServerBits emits server-level error_page + internal location.
 // Returns empty string when disabled, expand fails, or no codes remain.
+//
+// IMPORTANT: do NOT use `error_page CODE = /uri` (equals without response code).
+// That form adopts the status returned by the error URI; content_by_lua defaults
+// to 200 and ngx.status is often 0, so clients saw 200 with body "{{status}}"→"0".
+// Without `=`, nginx keeps the original error status for the internal redirect.
 func renderOriginErrorPageServerBits(cfg ConfigSnapshot) string {
 	if !cfg.OriginErrorPageEnabled {
 		return ""
@@ -148,31 +153,59 @@ func renderOriginErrorPageServerBits(cfg ConfigSnapshot) string {
 		parts[i] = strconv.Itoa(code)
 	}
 	var builder strings.Builder
-	fmt.Fprintf(&builder, "    error_page %s = %s;\n", strings.Join(parts, " "), OriginErrorPageInternalLocation)
+	// No `=` — preserve original error status (502 stays 502).
+	fmt.Fprintf(&builder, "    error_page %s %s;\n", strings.Join(parts, " "), OriginErrorPageInternalLocation)
 	builder.WriteString(renderOriginErrorPageInternalLocation())
 	return builder.String()
 }
 
 func renderOriginErrorPageInternalLocation() string {
+	// Resolve status from $status (set by error_page internal redirect), then
+	// upstream_status, then ngx.status. Force ngx.status so the client receives
+	// the real error code. Use function replacers so host/status with `%` are safe.
+	//
+	// Note: fmt.Sprintf is used only for the two path placeholders; Lua `%` must be
+	// written as `%%` so Sprintf does not treat them as format verbs.
 	return fmt.Sprintf(`    location = %s {
         internal;
         default_type text/html;
         charset utf-8;
         content_by_lua_block {
+            local function resolve_error_status()
+                local code = tonumber(ngx.var.status)
+                if code and code >= 400 then
+                    return code
+                end
+                local upstream = ngx.var.upstream_status or ""
+                -- multi-upstream: "502, 502" or failed connect "0"
+                local first = upstream:match("(%%d+)")
+                code = tonumber(first)
+                if code and code >= 400 then
+                    return code
+                end
+                code = tonumber(ngx.status)
+                if code and code >= 400 then
+                    return code
+                end
+                return 502
+            end
+
+            local code = resolve_error_status()
+            ngx.status = code
+
             local f = io.open("%s", "r")
             if not f then
-                ngx.status = ngx.status
-                ngx.say("Error ", ngx.status)
+                ngx.header["Content-Type"] = "text/html; charset=utf-8"
+                ngx.say("Error ", tostring(code))
                 return
             end
             local body = f:read("*a")
             f:close()
-            local status = tostring(ngx.status)
+            local status = tostring(code)
             local host = ngx.var.host or ""
-            body = body:gsub("{{status}}", status, 1)
-            body = body:gsub("{{host}}", host, 1)
-            body = body:gsub("{{status}}", status)
-            body = body:gsub("{{host}}", host)
+            -- function replacer: plain insert, no percent pattern side effects
+            body = body:gsub("{{status}}", function() return status end)
+            body = body:gsub("{{host}}", function() return host end)
             ngx.header["Content-Type"] = "text/html; charset=utf-8"
             ngx.say(body)
         }

pkg/render/openresty/origin_error_page_test.go

@@ -30,8 +30,19 @@ func TestRenderOriginErrorPageEnabled(t *testing.T) {
 	if !strings.Contains(out, "error_page 500") {
 		t.Fatalf("expected expanded status codes in error_page, got:\n%s", out)
 	}
-	if !strings.Contains(out, "= /__openflare_origin_error") {
-		t.Fatal("error_page must keep original status via = redirect form")
+	// Must NOT use `error_page … = /uri` (adopts error-URI status → often 200).
+	// `location = /path` is unrelated and expected.
+	for _, line := range strings.Split(out, "\n") {
+		trimmed := strings.TrimSpace(line)
+		if strings.HasPrefix(trimmed, "error_page ") && strings.Contains(trimmed, " = ") {
+			t.Fatalf("error_page must not use '=' form, got: %s", trimmed)
+		}
+	}
+	if !strings.Contains(out, "error_page ") || !strings.Contains(out, " /__openflare_origin_error;") {
+		t.Fatal("error_page must redirect to internal location without '='")
+	}
+	if !strings.Contains(out, "resolve_error_status") || !strings.Contains(out, "ngx.status = code") {
+		t.Fatal("internal location must resolve and set ngx.status to the original error code")
 	}
 	if !strings.Contains(out, ErrorPageTmplPlaceholder) {
 		t.Fatal("missing error page template placeholder")
@@ -151,8 +162,8 @@ func TestRenderOriginErrorPageCustomHTMLInSupportFile(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if !strings.Contains(out, "error_page 502 = /__openflare_origin_error") {
-		t.Fatalf("expected single 502 error_page, got:\n%s", out)
+	if !strings.Contains(out, "error_page 502 /__openflare_origin_error;") {
+		t.Fatalf("expected single 502 error_page without '=', got:\n%s", out)
 	}
 }