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>

Author: skarim

cmd/init.go

@@ -448,29 +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

@@ -798,26 +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)
-		})
-	}
-}