Judge the SDK conformance fixtures against the SDK the controller pins, never a desktop's checkout (issue 449)

A check clones mesh-sdk beside the controller at the commit go.mod pins; elsewhere
the test reads a copy captured at that commit, held to go.mod. A missing clone fails
instead of skipping.

cmd/mesh-controller/merge_gate_test.go

@@ -390,9 +390,10 @@ func TestAWithheldPathIsStoodInForByAPath(t *testing.T) {
 // controller's ask and by the facts — and finds the repository it checks from its origin.
 func TestACheckByHandClonesWhatTheSeatClones(t *testing.T) {
 	for dir, refs := range map[string]map[string]string{
-		"mesh-catalog":    {"mesh-catalog": "main"},
-		"mesh-host":       {"mesh-host": "c0ffee"},
-		"mesh-controller": {"mesh-controller": "c0ffee", "mesh-controller-main": "main", "mesh-lab": "main"},
+		"mesh-catalog": {"mesh-catalog": "main"},
+		"mesh-host":    {"mesh-host": "c0ffee"},
+		"mesh-controller": {"mesh-controller": "c0ffee", "mesh-controller-main": "main", "mesh-lab": "main",
+			"mesh-sdk": sdkPinnedByGoMod(t)},
 	} {
 		got := besideRefs(dir, "c0ffee")
 		for d, ref := range refs {
@@ -412,3 +413,24 @@ func TestACheckByHandClonesWhatTheSeatClones(t *testing.T) {
 		}
 	}
 }
+
+// sdkPinnedByGoMod is the SDK commit this tree's go.mod pins, read from the file rather than the build, so
+// sdkPinned is held to what the repository says (novox/hq issue 449).
+func sdkPinnedByGoMod(t *testing.T) string {
+	t.Helper()
+	raw, err := os.ReadFile(filepath.Join("..", "..", "go.mod"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, line := range strings.Split(string(raw), "\n") {
+		fields := strings.Fields(line)
+		if len(fields) >= 2 && fields[0] == sdkModule {
+			if m := pseudoCommit.FindStringSubmatch(fields[1]); m != nil {
+				return m[1]
+			}
+			return "go/" + fields[1]
+		}
+	}
+	t.Fatalf("go.mod requires no %s", sdkModule)
+	return ""
+}