fix: ensure .zshrc and brew shellenv exist after setup (#9)

- Stop renaming Oh-My-Zsh's .zshrc in InstallOhMyZsh (stow already
  handles backup), so .zshrc survives a fresh install
- Add EnsureBrewShellenv to write `eval "$(brew shellenv)"` into
  .zshrc on Apple Silicon — runs in both stepShell and stepRestoreShell
  regardless of Oh-My-Zsh choice
- Normalize bool values (1/0/yes/no → true/false) for `defaults write`
  so macos_prefs type=bool accepts all common representations

Author: fullstackjam

internal/installer/installer.go

@@ -609,27 +609,22 @@ func stepShell(cfg *config.Config) error {
 	ui.Header("Step 5: Shell Configuration")
 	fmt.Println()
 
-	// Smart detection: skip if Oh-My-Zsh is already installed
+	// Smart detection: skip Oh-My-Zsh if already installed
 	if shell.IsOhMyZshInstalled() && cfg.Shell == "" {
 		ui.Success("✓ Oh-My-Zsh already installed")
-		fmt.Println()
-		return nil
-	}
-
-	if cfg.Shell == "" {
+	} else if cfg.Shell == "" {
 		if cfg.Silent || (cfg.DryRun && !system.HasTTY()) {
 			cfg.Shell = "install"
 		} else {
 			install, err := ui.Confirm("Install Oh-My-Zsh and configure shell?", true)
 			if err != nil {
 				return err
 			}
-			if !install {
-				ui.Muted("Skipping shell configuration")
-				fmt.Println()
-				return nil
+			if install {
+				cfg.Shell = "install"
+			} else {
+				ui.Muted("Skipping Oh-My-Zsh")
 			}
-			cfg.Shell = "install"
 		}
 	}
 
@@ -646,6 +641,13 @@ func stepShell(cfg *config.Config) error {
 		}
 	}
 
+	// Ensure Homebrew shellenv is in .zshrc (required on Apple Silicon).
+	// Runs after Oh-My-Zsh so its .zshrc template exists, and regardless of
+	// the Oh-My-Zsh choice because brew must be in PATH for new shells.
+	if err := shell.EnsureBrewShellenv(cfg.DryRun); err != nil {
+		return fmt.Errorf("ensure brew shellenv: %w", err)
+	}
+
 	fmt.Println()
 	return nil
 }
@@ -954,6 +956,10 @@ func stepRestoreShell(cfg *config.Config) error {
 		return err
 	}
 
+	if err := shell.EnsureBrewShellenv(cfg.DryRun); err != nil {
+		return fmt.Errorf("ensure brew shellenv: %w", err)
+	}
+
 	if !cfg.DryRun {
 		ui.Success("Shell configuration restored")
 	}

internal/macos/macos.go

@@ -51,6 +51,17 @@ var DefaultPreferences = []Preference{
 	{"com.apple.TimeMachine", "DoNotOfferNewDisksForBackup", "bool", "true", "Don't prompt for Time Machine on new disks"},
 }
 
+func normalizeBool(value string) string {
+	switch strings.ToLower(value) {
+	case "1", "yes":
+		return "true"
+	case "0", "no":
+		return "false"
+	default:
+		return value
+	}
+}
+
 func InferPreferenceType(value string) string {
 	switch strings.ToLower(value) {
 	case "true", "false", "1", "0", "yes", "no":
@@ -105,7 +116,7 @@ func Configure(prefs []Preference, dryRun bool) error {
 		args := []string{"write", pref.Domain, pref.Key}
 		switch pref.Type {
 		case "bool":
-			args = append(args, "-bool", value)
+			args = append(args, "-bool", normalizeBool(value))
 		case "int":
 			args = append(args, "-int", value)
 		case "float":

internal/shell/shell.go

@@ -46,22 +46,53 @@ func InstallOhMyZsh(dryRun bool) error {
 	cmd := exec.Command("bash", "-c", script)
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr
-	if err := cmd.Run(); err != nil {
-		return err
+	return cmd.Run()
+}
+
+const brewShellenvLine = `eval "$(/opt/homebrew/bin/brew shellenv)"`
+
+// EnsureBrewShellenv adds the Homebrew shellenv eval to ~/.zshrc on Apple
+// Silicon if it isn't already present. This is required because /opt/homebrew
+// is not in the default PATH.
+func EnsureBrewShellenv(dryRun bool) error {
+	if _, err := os.Stat("/opt/homebrew/bin/brew"); os.IsNotExist(err) {
+		return nil // Intel Mac or no Homebrew — not needed
 	}
 
 	home, err := system.HomeDir()
 	if err != nil {
 		return err
 	}
 	zshrcPath := filepath.Join(home, ".zshrc")
-	if _, err := os.Stat(zshrcPath); err == nil {
-		if err := os.Rename(zshrcPath, zshrcPath+".openboot.bak"); err != nil {
-			return fmt.Errorf("backup %s: %w", zshrcPath, err)
+
+	// Create .zshrc if it doesn't exist.
+	if _, err := os.Stat(zshrcPath); os.IsNotExist(err) {
+		if dryRun {
+			fmt.Printf("[DRY-RUN] Would create %s with Homebrew shellenv\n", zshrcPath)
+			return nil
 		}
+		return os.WriteFile(zshrcPath, []byte(brewShellenvLine+"\n"), 0644)
 	}
 
-	return nil
+	raw, err := os.ReadFile(zshrcPath)
+	if err != nil {
+		return fmt.Errorf("read .zshrc: %w", err)
+	}
+	if strings.Contains(string(raw), "brew shellenv") {
+		return nil // already present
+	}
+
+	if dryRun {
+		fmt.Println("[DRY-RUN] Would add Homebrew shellenv to .zshrc")
+		return nil
+	}
+
+	content := string(raw)
+	if len(content) > 0 && content[len(content)-1] != '\n' {
+		content += "\n"
+	}
+	content = brewShellenvLine + "\n" + content
+	return os.WriteFile(zshrcPath, []byte(content), 0644)
 }
 
 func SetDefaultShell(dryRun bool) error {