Add TUI add and preview commands

Use charmbracelet/huh for an interactive add flow. Add a preview
subcommand to enter/exit per-project pre-release tags. Move stamp.toml
into .stamp/ and add ConfigPath helper. Prefer --snapshot then project
PreTag when computing versions and promote bumps to pre-release when
appropriate. Export CurrentVersion and add required TUI deps to go.mod.

internal/config/config.go

@@ -8,8 +8,15 @@ import (
 	"github.com/BurntSushi/toml"
 )
 
-const DefaultChangesetDir = ".stamp"
-const ConfigFileName = "stamp.toml"
+const (
+	DefaultChangesetDir = ".stamp"
+	ConfigFileName      = "stamp.toml"
+)
+
+// ConfigPath returns the path to stamp.toml inside the changeset directory.
+func ConfigPath(repoRoot string) string {
+	return filepath.Join(repoRoot, DefaultChangesetDir, ConfigFileName)
+}
 
 // Config is the root configuration parsed from stamp.toml.
 type Config struct {
@@ -19,8 +26,7 @@ type Config struct {
 
 // GlobalConfig holds repo-level settings.
 type GlobalConfig struct {
-	BaseBranch   string `toml:"base_branch,omitempty"`
-	ChangesetDir string `toml:"changeset_dir,omitempty"`
+	BaseBranch string `toml:"base_branch,omitempty"`
 }
 
 // Project represents a single project in the monorepo.
@@ -29,6 +35,7 @@ type Project struct {
 	Path      string        `toml:"path"`
 	Version   string        `toml:"version"`
 	Changelog string        `toml:"changelog,omitempty"`
+	PreTag    string        `toml:"pre_tag,omitempty"`
 	Publish   PublishConfig `toml:"publish,omitempty"`
 }
 
@@ -39,11 +46,9 @@ type PublishConfig struct {
 	Artifacts []string `toml:"artifacts"`
 }
 
-// ChangesetDir returns the configured changeset directory, defaulting to .stamp.
+// ChangesetDir always returns the default changeset directory.
+// The config file lives inside this directory, so it is always known.
 func (c *Config) ChangesetDir() string {
-	if c.Config.ChangesetDir != "" {
-		return c.Config.ChangesetDir
-	}
 	return DefaultChangesetDir
 }
 
@@ -93,9 +98,9 @@ func (p *PublishConfig) PublishReleases() bool {
 	return p.Releases == nil || *p.Releases
 }
 
-// Load reads and validates stamp.toml from the given directory.
-func Load(dir string) (*Config, error) {
-	path := filepath.Join(dir, ConfigFileName)
+// Load reads and validates stamp.toml from inside the changeset directory.
+func Load(repoRoot string) (*Config, error) {
+	path := ConfigPath(repoRoot)
 	data, err := os.ReadFile(path)
 	if err != nil {
 		return nil, fmt.Errorf("reading %s: %w", path, err)
@@ -113,9 +118,13 @@ func Load(dir string) (*Config, error) {
 	return &cfg, nil
 }
 
-// Save writes the config back to stamp.toml in the given directory.
-func Save(dir string, cfg *Config) error {
-	path := filepath.Join(dir, ConfigFileName)
+// Save writes the config back to stamp.toml inside the changeset directory.
+func Save(repoRoot string, cfg *Config) error {
+	dir := filepath.Join(repoRoot, DefaultChangesetDir)
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return fmt.Errorf("creating %s: %w", dir, err)
+	}
+	path := ConfigPath(repoRoot)
 	f, err := os.Create(path)
 	if err != nil {
 		return fmt.Errorf("creating %s: %w", path, err)

internal/config/config_test.go

@@ -11,7 +11,6 @@ import (
 const validTOML = `
 [config]
 base_branch = "main"
-changeset_dir = ".stamp"
 
 [[projects]]
 name    = "my-app"
@@ -24,11 +23,20 @@ path    = "libs/my-lib"
 version = "0.1.0"
 `
 
-func TestLoad_Valid(t *testing.T) {
-	dir := t.TempDir()
-	if err := os.WriteFile(filepath.Join(dir, "stamp.toml"), []byte(validTOML), 0o644); err != nil {
+func writeConfig(t *testing.T, dir, content string) {
+	t.Helper()
+	stampDir := filepath.Join(dir, ".stamp")
+	if err := os.MkdirAll(stampDir, 0o755); err != nil {
 		t.Fatal(err)
 	}
+	if err := os.WriteFile(filepath.Join(stampDir, "stamp.toml"), []byte(content), 0o644); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestLoad_Valid(t *testing.T) {
+	dir := t.TempDir()
+	writeConfig(t, dir, validTOML)
 
 	cfg, err := config.Load(dir)
 	if err != nil {
@@ -42,16 +50,14 @@ func TestLoad_Valid(t *testing.T) {
 		t.Errorf("expected base_branch=main, got %s", cfg.BaseBranch())
 	}
 	if cfg.ChangesetDir() != ".stamp" {
-		t.Errorf("expected changeset_dir=.stamp, got %s", cfg.ChangesetDir())
+		t.Errorf("expected ChangesetDir=.stamp, got %s", cfg.ChangesetDir())
 	}
 }
 
 func TestLoad_Defaults(t *testing.T) {
 	dir := t.TempDir()
 	minimal := "[[projects]]\nname = \"app\"\npath = \".\"\nversion = \"1.0.0\"\n"
-	if err := os.WriteFile(filepath.Join(dir, "stamp.toml"), []byte(minimal), 0o644); err != nil {
-		t.Fatal(err)
-	}
+	writeConfig(t, dir, minimal)
 
 	cfg, err := config.Load(dir)
 	if err != nil {
@@ -75,9 +81,7 @@ func TestLoad_MissingFile(t *testing.T) {
 
 func TestLoad_NoProjects(t *testing.T) {
 	dir := t.TempDir()
-	if err := os.WriteFile(filepath.Join(dir, "stamp.toml"), []byte("[config]\n"), 0o644); err != nil {
-		t.Fatal(err)
-	}
+	writeConfig(t, dir, "[config]\n")
 	_, err := config.Load(dir)
 	if err == nil {
 		t.Fatal("expected error for config with no projects")
@@ -97,9 +101,7 @@ name = "app"
 path = "other"
 version = "2.0.0"
 `
-	if err := os.WriteFile(filepath.Join(dir, "stamp.toml"), []byte(dup), 0o644); err != nil {
-		t.Fatal(err)
-	}
+	writeConfig(t, dir, dup)
 	_, err := config.Load(dir)
 	if err == nil {
 		t.Fatal("expected error for duplicate project name")
@@ -108,9 +110,7 @@ version = "2.0.0"
 
 func TestFindProject(t *testing.T) {
 	dir := t.TempDir()
-	if err := os.WriteFile(filepath.Join(dir, "stamp.toml"), []byte(validTOML), 0o644); err != nil {
-		t.Fatal(err)
-	}
+	writeConfig(t, dir, validTOML)
 	cfg, _ := config.Load(dir)
 
 	if p := cfg.FindProject("my-app"); p == nil {

internal/semver/semver.go

@@ -9,6 +9,12 @@ import (
 	"git.thokra.dev/thokra/stamp/internal/changeset"
 )
 
+// CurrentVersion parses a version string and returns the semver object.
+// It is exported so callers can inspect pre-release state without re-importing the semver library.
+func CurrentVersion(version string) (*goSemver.Version, error) {
+	return goSemver.NewVersion(version)
+}
+
 // Bump computes the next version given the current version string and a bump type.
 // preID is the pre-release identifier (e.g. "alpha", "beta", "rc") used for pre-* bumps.
 func Bump(current string, bump changeset.BumpType, preID string) (string, error) {