Bring F3 up to its release branch, with both sides' store tests (part 5 of 14)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/builder/check_test.go

@@ -590,3 +590,15 @@ func TestARepositoryInTwoLanguagesIsCheckedInBoth(t *testing.T) {
 		t.Errorf("a part in a toolchain the mesh does not hold answered %+v — never a pass", layer)
 	}
 }
+
+// A branch tried before its pull request may narrow what the repository's script runs (novox/hq issue 686); a
+// pull request's check is handed nothing, and runs whole.
+func TestOnlyATrysSelectionReachesTheScript(t *testing.T) {
+	if env := selection(CheckSpec{Number: 7}); len(env) != 0 {
+		t.Fatalf("a pull request's check was handed a selection: %v", env)
+	}
+	env := selection(CheckSpec{Tests: "^TestX$", StoreOnly: true})
+	if len(env) != 2 || env[0] != "MESH_CHECK_TESTS=^TestX$" || env[1] != "MESH_CHECK_STORE_ONLY=1" {
+		t.Fatalf("a try's selection: %v", env)
+	}
+}