Publish Tentacle fixture markers atomically and patch the release package

internal/app/tentacle_interaction_test.go

@@ -32,7 +32,9 @@ func TestTentacleInteractionPeer(t *testing.T) {
 		return sdk.Interaction{Form: &sdk.Form{Title: "Wormhole menu", Elements: []sdk.Element{{ID: "code", Label: "Wormhole code", Kind: sdk.Entry, Required: true, MaxLength: 256}}}, Next: next}, nil
 	}
 	submit := func(_ context.Context, raw json.RawMessage) (any, error) {
-		os.WriteFile(marker, raw, 0600)
+		if err := write_tentacle_fixture_marker(marker, raw); err != nil {
+			return nil, err
+		}
 		return sdk.Interaction{Presentation: sdk.Presentation{Speech: "Submitted", Braille: "Submitted"}}, nil
 	}
 	commands := []sdk.Command{

internal/app/tentacles_test.go

@@ -19,6 +19,14 @@ import (
 	sdk "git.stormux.org/storm/cthulhu/sdk/go/tentacle"
 )
 
+// Publish complete fixture data before readers can observe the marker.
+func write_tentacle_fixture_marker(markerPath string, data []byte) error {
+	if err := os.WriteFile(markerPath+".tmp", data, 0600); err != nil {
+		return err
+	}
+	return os.Rename(markerPath+".tmp", markerPath)
+}
+
 // Subprocess fixture: no reader backend, network, or desktop access.
 func TestTentacleReaderPeer(t *testing.T) {
 	if len(os.Args) < 3 || os.Args[len(os.Args)-2] != "reader-peer" {
@@ -41,7 +49,7 @@ func TestTentacleReaderPeer(t *testing.T) {
 				os.Exit(3)
 			}
 			group, _ := os.ReadFile("/proc/self/cgroup")
-			if err := os.WriteFile(marker, group, 0600); err != nil {
+			if err := write_tentacle_fixture_marker(marker, group); err != nil {
 				return nil, err
 			}
 			if filepath.Base(marker) == "present-delay" {