enforce lifecycle contracts and scratch transport

internal/continuity/continuity.go

@@ -194,6 +194,16 @@ func ScratchCommit(root, branch, message string) error {
 	if strings.TrimSpace(message) == "" {
 		return errors.New("scratch commit message required")
 	}
+	status, err := exec.Command("git", "-C", root, "status", "--porcelain", "--", "TASK.md").Output()
+	if err != nil {
+		return err
+	}
+	if len(status) != 0 {
+		return errors.New("TASK.md is immutable")
+	}
+	if strings.TrimSpace(message) == "" {
+		return errors.New("scratch commit message required")
+	}
 	for _, args := range [][]string{{"switch", "-c", branch}, {"add", "-A"}, {"commit", "-m", message}} {
 		if err := exec.Command("git", append([]string{"-C", root}, args...)...).Run(); err != nil {
 			return err
@@ -202,6 +212,23 @@ func ScratchCommit(root, branch, message string) error {
 	return nil
 }
 
+func ScratchPush(root, branch, remote string) error {
+	if branch == "" || remote == "" {
+		return errors.New("scratch branch and remote required")
+	}
+	return exec.Command("git", "-C", root, "push", remote, branch).Run()
+}
+
+func ScratchPull(root, branch, remote string) error {
+	if branch == "" || remote == "" {
+		return errors.New("scratch branch and remote required")
+	}
+	if err := exec.Command("git", "-C", root, "fetch", remote, branch).Run(); err != nil {
+		return err
+	}
+	return exec.Command("git", "-C", root, "merge", "--ff-only", "FETCH_HEAD").Run()
+}
+
 // ScratchSync pushes/pulls a scratch branch. Pull uses fast-forward-only to
 // avoid silently merging independent WIP histories.
 func ScratchSync(root, branch, remote string, push bool) error {