fix: Eliminate compatibility risk of matching all domains for an MCP server (#2973)

pkg/ingress/kube/annotations/mcpserver.go

@@ -53,7 +53,8 @@ func (a mcpServer) Parse(annotations Annotations, config *Ingress, globalContext
 	var matchRuleDomains []string
 	rawMatchRuleDomains, _ := annotations.ParseStringASAP(mcpServerMatchRuleDomains)
 	if rawMatchRuleDomains == "" || rawMatchRuleDomains == "*" {
-		// Match all domains. Leave an empty slice.
+		// Use wildcard to match all domains so we don't rely on the default behavior of empty domain list
+		matchRuleDomains = []string{"*"}
 	} else if strings.Contains(rawMatchRuleDomains, ",") {
 		matchRuleDomains = strings.Split(rawMatchRuleDomains, ",")
 	} else {

pkg/ingress/kube/annotations/mcpserver_test.go

@@ -132,7 +132,7 @@ func TestMCPServer_Parse(t *testing.T) {
 			},
 			expect: &mcpserver.McpServer{
 				Name:              "default/route",
-				Domains:           nil,
+				Domains:           []string{"*"},
 				PathMatchType:     "prefix",
 				PathMatchValue:    "/mcp",
 				UpstreamType:      "rest",
@@ -153,7 +153,7 @@ func TestMCPServer_Parse(t *testing.T) {
 			},
 			expect: &mcpserver.McpServer{
 				Name:              "default/route",
-				Domains:           nil,
+				Domains:           []string{"*"},
 				PathMatchType:     "prefix",
 				PathMatchValue:    "/mcp",
 				UpstreamType:      "rest",