fix(builder): SteamCMD is the only option for Linux Steam servers; settings must reach the server

cmd/gbrgames/research_test.go

@@ -59,10 +59,10 @@ func TestParseAppInfoFindsLinuxServers(t *testing.T) {
 	}
 }
 
-func TestWithSteamCMDGoesFirstOnlyForLinuxServers(t *testing.T) {
+func TestWithSteamCMDIsTheOnlyRouteForLinuxServers(t *testing.T) {
 	images := []string{"someone/example-server", "cm2network/steamcmd", "other/example"}
 	got := withSteamCMD(images, true)
-	if len(got) != 3 || got[0] != "cm2network/steamcmd" || got[1] != "someone/example-server" {
+	if len(got) != 1 || got[0] != "cm2network/steamcmd" {
 		t.Errorf("linux: %v", got)
 	}
 	got = withSteamCMD([]string{"someone/proton-example"}, false)
@@ -89,10 +89,22 @@ func TestRecommendPrefersTheSteamCMDVariant(t *testing.T) {
 	}
 }
 
+func TestSteamCMDOnlyDropsImageVariantsOfLinuxSteamGames(t *testing.T) {
+	// A Linux Steam server researched as two variants: SteamCMD, and a community image under its own title
+	got := steamCMDOnly([]variant{
+		{ID: "dedicated", SteamAppID: "1000000", Images: []string{"cm2network/steamcmd"}},
+		{ID: "vanilla-stable", Images: []string{"someone/example-server"}},
+	})
+	if len(got) != 1 || got[0].ID != "dedicated" {
+		t.Errorf("got %+v", got)
+	}
+}
+
 func TestOneOptionPerImageThenSteamCMDRecommended(t *testing.T) {
+	// A variant runnable two ways becomes one option per way, SteamCMD recommended
 	v := oneOptionPerImage([]variant{{
 		ID: "dedicated", Title: "Example Dedicated Server", Recommended: true, SteamAppID: "1000000",
-		Images:   withSteamCMD([]string{"someone/example-server"}, true),
+		Images:   []string{"cm2network/steamcmd", "someone/example-server"},
 		Verified: []string{"image someone/example-server exists", "Steam app 1000000 is \"Example Dedicated Server\""},
 	}})
 	recommend(v)