remove silent prefix detection in init (#126)

* Remove silent prefix detection from args path in init

When explicit branch names containing slashes were passed to `gh stack
init` (e.g. `gh stack init myprefix/branch`), detectPrefix would
silently extract the prefix and store it in the stack config. This
caused `gh stack add otherbranch` to unexpectedly produce
`myprefix/otherbranch` without the user ever opting in.

Remove the automatic prefix detection from the args path so that
explicit branch names are taken literally. Users who want a prefix
should use `--prefix`. The interactive path (no args) continues to
prompt for confirmation before setting a prefix.

* Remove dead detectPrefix function and its tests

After removing the silent prefix detection from the args path,
detectPrefix has no production callers. Remove the function and
its table-driven unit test to avoid maintaining unused code.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

cmd/init.go

@@ -149,13 +149,6 @@ func runInit(cfg *config.Config, opts *initOptions) error {
 			return err
 		}
 
-		// Prefix detection (only when --prefix not explicitly set)
-		if opts.prefix == "" {
-			if detected := detectPrefix(branches); detected != "" {
-				opts.prefix = detected
-			}
-		}
-
 	} else if opts.numbered {
 		// === NUMBERED PATH (unchanged) ===
 		if opts.prefix == "" && cfg.IsInteractive() {
@@ -455,29 +448,6 @@ func promptBranchName(cfg *config.Config, prefix string) (string, error) {
 	return branchName, nil
 }
 
-// detectPrefix finds a common prefix across branches by splitting each
-// at its last slash. Returns the prefix (without trailing slash) if all
-// branches share the same one, or "" otherwise.
-func detectPrefix(branches []string) string {
-	if len(branches) == 0 {
-		return ""
-	}
-	var common string
-	for i, b := range branches {
-		lastSlash := strings.LastIndex(b, "/")
-		if lastSlash <= 0 {
-			return "" // no slash or leading slash — no prefix
-		}
-		prefix := b[:lastSlash]
-		if i == 0 {
-			common = prefix
-		} else if prefix != common {
-			return "" // different prefixes
-		}
-	}
-	return common
-}
-
 // printWhatsNext prints the scenario-aware "What's next" block after init.
 func printWhatsNext(cfg *config.Config, s *stack.Stack, branches []string, hasAdopted bool, prCount int) {
 	lastBranch := branches[len(branches)-1]

cmd/init_test.go

@@ -465,7 +465,9 @@ func TestInit_ImplicitAdopt_Mixed(t *testing.T) {
 }
 
 func TestInit_PrefixDetection_ArgsCommonPrefix(t *testing.T) {
-	// Scenario 9: args all share prefix → set silently
+	// Explicit branch names with a common prefix should NOT auto-detect
+	// a prefix — the slash is part of the branch name, not a convention.
+	// Users who want a prefix should use --prefix.
 	gitDir := t.TempDir()
 	restore := git.SetOps(&git.MockOps{
 		GitDirFn:        func() (string, error) { return gitDir, nil },
@@ -481,7 +483,7 @@ func TestInit_PrefixDetection_ArgsCommonPrefix(t *testing.T) {
 
 	require.NoError(t, err)
 	sf, _ := stack.Load(gitDir)
-	assert.Equal(t, "feat", sf.Stacks[0].Prefix)
+	assert.Equal(t, "", sf.Stacks[0].Prefix)
 }
 
 func TestInit_PrefixDetection_ArgsMixedPrefix(t *testing.T) {
@@ -525,7 +527,8 @@ func TestInit_PrefixDetection_ArgsNoSlash(t *testing.T) {
 }
 
 func TestInit_PrefixDetection_NestedPrefix(t *testing.T) {
-	// Scenario 6: sameen/feat/x → prefix "sameen/feat"
+	// Explicit branch names with nested slashes should NOT auto-detect
+	// a prefix — the user typed the full branch name deliberately.
 	gitDir := t.TempDir()
 	restore := git.SetOps(&git.MockOps{
 		GitDirFn:        func() (string, error) { return gitDir, nil },
@@ -541,7 +544,7 @@ func TestInit_PrefixDetection_NestedPrefix(t *testing.T) {
 
 	require.NoError(t, err)
 	sf, _ := stack.Load(gitDir)
-	assert.Equal(t, "sameen/feat", sf.Stacks[0].Prefix)
+	assert.Equal(t, "", sf.Stacks[0].Prefix)
 }
 
 func TestInit_ExplicitPrefixSkipsDetection(t *testing.T) {
@@ -795,26 +798,3 @@ func TestInit_TwoPassValidation_InvalidRefName(t *testing.T) {
 	assert.Contains(t, output, "invalid branch name")
 	assert.Empty(t, created, "no branches should be created when an arg has an invalid ref name")
 }
-
-func TestDetectPrefix(t *testing.T) {
-	tests := []struct {
-		name     string
-		branches []string
-		want     string
-	}{
-		{"common prefix", []string{"feat/a", "feat/b", "feat/c"}, "feat"},
-		{"nested prefix", []string{"sameen/feat/a", "sameen/feat/b"}, "sameen/feat"},
-		{"mixed prefixes", []string{"feat/a", "bug/b"}, ""},
-		{"no slashes", []string{"auth", "api", "ui"}, ""},
-		{"empty list", []string{}, ""},
-		{"single branch with slash", []string{"feat/x"}, "feat"},
-		{"single branch no slash", []string{"auth"}, ""},
-		{"leading slash only", []string{"/x"}, ""},
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			got := detectPrefix(tt.branches)
-			assert.Equal(t, tt.want, got)
-		})
-	}
-}