Bump version to 1.2.0

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

PLAN.md

@@ -1,158 +1,154 @@
-# arca — v1.0.0 Plan
+# arca — Post-1.0 Plan
 
-## Current State (v0.1.0)
+## Current State (v1.0.0)
 
-Working proof of concept. FIDO2 unlock via cryptsetup with passphrase
+Released. FIDO2/passphrase/keyfile/TPM2 unlock with method sequencing,
-fallback, privileged mount/unmount, config aliases with method
+idempotent mount/unmount, config aliases, init command, status command,
-sequencing, init and status commands.
+NixOS LD_LIBRARY_PATH workaround for cryptsetup token plugins, unit
-
+tests, nix flake packaging.
-## M1: Idempotent mount/unmount
-
-`mount` and `unmount` should be safe to run at any point in a device's
-lifecycle without producing confusing errors.
-
-### Files changed
-
-- `cmd/mount.go`
-- `cmd/unmount.go`
-- `internal/udisks/client.go`
-
-### Work
-
-1. In `runMount`, after `FindDevice`, check if the device is already
-   unlocked (`CleartextDevice` succeeds). If the cleartext device is
-   already mounted, print the existing mount point and return success.
-   If unlocked but not mounted, skip unlock and go straight to mount.
-
-2. In `runUnmount`, handle each failure case:
-   - `CleartextDevice` fails (already locked): print "already locked"
-     and return success.
-   - `Unmount` fails because not mounted: proceed to lock anyway.
-   - `Lock` fails because already locked: return success.
-
-3. Add `client.IsMounted(dev)` helper that returns `(mountpoint, bool)`
-   to reduce duplicated mount-point checking logic.
 
 ---
 
-## M2: Error messages
+## v1.1: Shell completions and verbose mode
 
-Replace generic D-Bus errors with actionable messages.
+### M6: Shell completions
 
-### Files changed
+Cobra generates completion scripts. Wire them up so alias names
+complete in the shell.
 
-- `internal/udisks/client.go`
+#### Files changed
-- `cmd/mount.go`, `cmd/unmount.go`, `cmd/init.go`, `cmd/status.go`
-
-### Work
-
-1. Wrap the `dbus.SystemBus()` error in `NewClient` to detect
-   "connection refused" or "no such file" and print:
-   `"cannot connect to udisks2 — is the udisks2 service running?"`
-
-2. In `FindDevice`, when no device matches, include what was searched
-   and suggest `arca status` or `arca init`:
-   `"device /dev/sda1 not found (run 'arca status' to list devices)"`
-
-3. In the unlock sequencer, prefix each method error with context:
-   `"fido2: cryptsetup open --token-only: exit status 5 (is the FIDO2 key plugged in?)"`
-
----
-
-## M3: Unit tests
-
-Cover pure logic that doesn't need D-Bus or real devices.
-
-### Files changed
-
-- `internal/config/config_test.go` (new)
-- `internal/cryptsetup/cryptsetup_test.go` (new)
-
-### Work
-
-1. **config_test.go** — test cases:
-   - `ResolveDevice` with exact alias match
-   - `ResolveDevice` with device path match (`/dev/sda1` -> `sda1`)
-   - `ResolveDevice` with unknown name returns default methods
-   - `ResolveDevice` with empty methods list defaults to `[passphrase]`
-   - `AliasFor` finds alias by UUID
-   - `AliasFor` returns "" for unknown UUID
-   - `Load` with nonexistent file returns empty config
-   - `Load` with valid YAML parses correctly
-
-2. **cryptsetup_test.go** — test cases:
-   - `MapperName("/dev/sda1")` == `"arca-sda1"`
-   - `MapperName("/dev/nvme0n1p2")` == `"arca-nvme0n1p2"`
-   - `hasTokenPlugins` with a temp dir containing a matching .so
-   - `hasTokenPlugins` with an empty temp dir
-
----
-
-## M4: CLI polish
-
-Small usability improvements.
-
-### Files changed
 
 - `cmd/root.go`
-- `cmd/mount.go`
-- `cmd/init.go`
-- `main.go`
-- `.gitignore` (new)
-
-### Work
-
-1. Add `var version = "dev"` to `main.go`. Set `rootCmd.Version` in
-   `cmd/root.go`. Build with `-ldflags "-X main.version=..."` in
-   `flake.nix`.
-
-2. Add `--mountpoint` / `-m` flag to `mount` subcommand. When set,
-   pass it to `cryptsetup.Mount` (privileged path) or log a warning
-   that udisks2 doesn't support custom mount points.
-
-3. In `init`, use first 8 chars of UUID as alias instead of device
-   path basename. Example: `b8b2f8e3` instead of `sda1`. UUIDs are
-   stable across boots; device paths are not.
-
-4. Create `.gitignore` containing `/arca`.
-
----
-
-## M5: Documentation and packaging
-
-Make the project installable and the README trustworthy.
-
-### Files changed
-
-- `README.md`
 - `flake.nix`
 
-### Work
+#### Work
 
-1. Update `README.md`:
+1. Cobra provides `completion` subcommand by default (`arca completion
-   - Replace placeholder UUIDs with realistic examples from actual
+   zsh`, `arca completion bash`, etc.). Verify it works.
-     tested usage.
-   - Add "NixOS notes" section documenting the `LD_LIBRARY_PATH`
-     requirement for FIDO2/TPM2 and why `--external-tokens-path`
-     doesn't work.
-   - Add "Troubleshooting" section: no FIDO2 token enrolled, udisks2
-     not running, permission denied on mount.
-   - Document `init` subcommand.
 
-2. Verify `flake.nix`:
+2. Add a custom `ValidArgsFunction` to `mountCmd` and `unmountCmd`
-   - Run `nix build` and confirm it produces a working binary.
+   that reads the config and returns alias names + device paths from
-   - Add `-ldflags` for version injection from `self.rev` or a
+   `arca status`. This gives dynamic completion for:
-     `version` variable.
+   ```
-   - Test the flake output: `./result/bin/arca --version`.
+   arca mount <TAB>   -> backup  media  /dev/sda1
+   arca unmount <TAB> -> backup  media
+   ```
 
-3. Tag `v1.0.0`.
+3. In `flake.nix`, install the zsh completion file to
+   `$out/share/zsh/site-functions/_arca` so NixOS picks it up
+   automatically.
+
+### M7: Verbose mode
+
+Add `-v` / `--verbose` flag to aid debugging (e.g., the FIDO2 plugin
+discovery issue we hit during development).
+
+#### Files changed
+
+- `cmd/root.go`
+- `internal/cryptsetup/cryptsetup.go`
+- `internal/unlock/unlock.go`
+- `internal/udisks/client.go`
+
+#### Work
+
+1. Add a `--verbose` / `-v` persistent flag on the root command. Store
+   in a package-level `Verbose bool`.
+
+2. In `cryptsetup.Open`: print the full command being executed
+   (including `LD_LIBRARY_PATH` and privilege wrapper).
+
+3. In `findTokenPluginDir`: print which directory was found (or that
+   none was found).
+
+4. In `unlock.Unlock`: print which method is being attempted before
+   each try.
+
+5. In `udisks.NewClient`: print the D-Bus connection status.
+
+Use `fmt.Fprintf(os.Stderr, "arca: ...")` for verbose output — no
+logging framework needed.
 
 ---
 
-## Non-goals for v1.0.0
+## v1.2: Config management and cleanup
+
+### M8: `arca add <device>`
+
+Add a single device to an existing config without regenerating
+everything.
+
+#### Files changed
+
+- `cmd/add.go` (new)
+- `internal/config/config.go`
+
+#### Work
+
+1. New subcommand: `arca add /dev/sda1` or `arca add --uuid <uuid>`.
+
+2. Resolve the device via udisks2 to get UUID.
+
+3. Generate a UUID-prefix alias (same as `init`).
+
+4. Prompt for alias name (default: UUID prefix), methods (default:
+   passphrase), and optional mountpoint.
+
+5. Append to existing config. If the UUID is already configured, print
+   the existing alias and exit.
+
+6. Add `config.Save(*Config)` to write the config file (currently
+   only `init` writes, with inline marshaling).
+
+### M9: `init --merge`
+
+Merge newly discovered devices into an existing config without
+overwriting existing entries.
+
+#### Files changed
+
+- `cmd/init.go`
+- `internal/config/config.go`
+
+#### Work
+
+1. Add `--merge` flag to `init`. When set, load existing config
+   first.
+
+2. For each discovered device, skip if its UUID already exists in
+   config (regardless of alias name).
+
+3. Add new devices with UUID-prefix aliases.
+
+4. Write the merged config.
+
+This replaces the current `--force` behavior for the common case of
+"I plugged in a new drive."
+
+### M10: Mount cleanup
+
+Privileged unmount leaves empty directories under `/mnt/`.
+
+#### Files changed
+
+- `internal/cryptsetup/cryptsetup.go`
+- `cmd/unmount.go`
+
+#### Work
+
+1. After `Unmount`, attempt `rmdir` on the mount point. Only remove
+   if empty (not `rm -rf`).
+
+2. Use privileged `rmdir` since the directory was created with
+   privilege.
+
+---
+
+## Non-goals
 
 - `--dry-run` flag
 - `--json` output for `status`
 - udev auto-mount on plug
 - Keyfile creation/management
 - Multiple config files or config includes
+- Systemd mount unit integration

cmd/add.go

@@ -0,0 +1,87 @@
+package cmd
+
+import (
+	"fmt"
+	"strings"
+
+	"git.wntrmute.dev/kyle/arca/internal/config"
+	"git.wntrmute.dev/kyle/arca/internal/udisks"
+	"github.com/spf13/cobra"
+)
+
+var addAlias string
+
+var addCmd = &cobra.Command{
+	Use:   "add <device>",
+	Short: "Add a device to the config",
+	Long:  "Detects a LUKS device via udisks2 and adds it to the config file with a default passphrase method.",
+	Args:  cobra.ExactArgs(1),
+	RunE:  runAdd,
+}
+
+func init() {
+	addCmd.Flags().StringVarP(&addAlias, "alias", "a", "", "alias name (default: first 8 chars of UUID)")
+	rootCmd.AddCommand(addCmd)
+}
+
+func runAdd(cmd *cobra.Command, args []string) error {
+	target := args[0]
+
+	client, err := udisks.NewClient()
+	if err != nil {
+		return fmt.Errorf("connecting to udisks2: %w", err)
+	}
+	defer client.Close()
+
+	// Find the device to get its UUID.
+	dev, err := client.FindDevice("", target)
+	if err != nil {
+		return err
+	}
+
+	if !dev.HasEncrypted {
+		return fmt.Errorf("%s is not a LUKS-encrypted device", target)
+	}
+
+	if dev.UUID == "" {
+		return fmt.Errorf("%s has no UUID", target)
+	}
+
+	cfg := config.Load()
+
+	// Check if already configured.
+	if existing := cfg.AliasFor(dev.UUID); existing != "" {
+		fmt.Printf("Device %s (UUID %s) already configured as %q\n", dev.DevicePath, dev.UUID, existing)
+		return nil
+	}
+
+	alias := addAlias
+	if alias == "" {
+		alias = aliasFromUUID(dev.UUID)
+	}
+
+	// Check for alias collision.
+	if _, exists := cfg.Devices[alias]; exists {
+		return fmt.Errorf("alias %q already in use — choose a different name with --alias", alias)
+	}
+
+	cfg.Devices[alias] = config.DeviceConfig{
+		UUID:    dev.UUID,
+		Methods: []string{"passphrase"},
+	}
+
+	if err := cfg.Save(); err != nil {
+		return fmt.Errorf("saving config: %w", err)
+	}
+
+	fmt.Printf("Added %s (UUID %s) as %q\n", dev.DevicePath, dev.UUID, alias)
+	return nil
+}
+
+func aliasFromUUID(uuid string) string {
+	clean := strings.ReplaceAll(uuid, "-", "")
+	if len(clean) > 8 {
+		clean = clean[:8]
+	}
+	return clean
+}

cmd/completion.go

@@ -0,0 +1,25 @@
+package cmd
+
+import (
+	"sort"
+
+	"git.wntrmute.dev/kyle/arca/internal/config"
+	"github.com/spf13/cobra"
+)
+
+// completeDeviceOrAlias provides dynamic completion for device aliases
+// and device paths from the config file.
+func completeDeviceOrAlias(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+	if len(args) > 0 {
+		return nil, cobra.ShellCompDirectiveNoFileComp
+	}
+
+	cfg := config.Load()
+	var completions []string
+	for alias := range cfg.Devices {
+		completions = append(completions, alias)
+	}
+	sort.Strings(completions)
+
+	return completions, cobra.ShellCompDirectiveNoFileComp
+}

cmd/init.go

@@ -3,18 +3,17 @@ package cmd
 import (
 	"fmt"
 	"os"
-	"path/filepath"
-	"strings"
-
 
 	"git.wntrmute.dev/kyle/arca/internal/config"
 	"git.wntrmute.dev/kyle/arca/internal/udisks"
 	"github.com/godbus/dbus/v5"
 	"github.com/spf13/cobra"
-	"gopkg.in/yaml.v3"
 )
 
-var forceInit bool
+var (
+	forceInit bool
+	mergeInit bool
+)
 
 var initCmd = &cobra.Command{
 	Use:   "init",
@@ -25,17 +24,26 @@ var initCmd = &cobra.Command{
 
 func init() {
 	initCmd.Flags().BoolVarP(&forceInit, "force", "f", false, "overwrite existing config file")
+	initCmd.Flags().BoolVar(&mergeInit, "merge", false, "add new devices to existing config without overwriting")
+	initCmd.MarkFlagsMutuallyExclusive("force", "merge")
 	rootCmd.AddCommand(initCmd)
 }
 
 func runInit(cmd *cobra.Command, args []string) error {
 	cfgPath := config.Path()
 
+	// Load existing config for merge, or start fresh.
+	var cfg *config.Config
+	if mergeInit {
+		cfg = config.Load()
+	} else {
 		if !forceInit {
 			if _, err := os.Stat(cfgPath); err == nil {
-			return fmt.Errorf("config already exists at %s (use --force to overwrite)", cfgPath)
+				return fmt.Errorf("config already exists at %s (use --force to overwrite or --merge to add new devices)", cfgPath)
 			}
 		}
+		cfg = &config.Config{Devices: make(map[string]config.DeviceConfig)}
+	}
 
 	client, err := udisks.NewClient()
 	if err != nil {
@@ -53,43 +61,42 @@ func runInit(cmd *cobra.Command, args []string) error {
 		return fmt.Errorf("detecting root device: %w", err)
 	}
 
-	cfg := config.Config{
+	added := 0
-		Devices: make(map[string]config.DeviceConfig),
-	}
-
 	for _, dev := range encrypted {
 		if isRootBacking(dev.ObjectPath, rootBacking) {
 			fmt.Fprintf(os.Stderr, "Skipping %s (root filesystem)\n", dev.DevicePath)
 			continue
 		}
 
+		if cfg.HasUUID(dev.UUID) {
+			fmt.Fprintf(os.Stderr, "Skipping %s (already configured)\n", dev.DevicePath)
+			continue
+		}
+
 		alias := aliasFromUUID(dev.UUID)
 		cfg.Devices[alias] = config.DeviceConfig{
 			UUID:    dev.UUID,
 			Methods: []string{"passphrase"},
 		}
 		fmt.Fprintf(os.Stderr, "Found %s (UUID %s) -> alias %q\n", dev.DevicePath, dev.UUID, alias)
+		added++
 	}
 
-	if len(cfg.Devices) == 0 {
+	if added == 0 && !mergeInit {
 		fmt.Println("No non-root LUKS devices found.")
 		return nil
 	}
 
-	data, err := yaml.Marshal(&cfg)
+	if added == 0 && mergeInit {
-	if err != nil {
+		fmt.Println("No new devices to add.")
-		return fmt.Errorf("marshaling config: %w", err)
+		return nil
 	}
 
-	if err := os.MkdirAll(filepath.Dir(cfgPath), 0o755); err != nil {
+	if err := cfg.Save(); err != nil {
-		return fmt.Errorf("creating config directory: %w", err)
+		return fmt.Errorf("saving config: %w", err)
 	}
 
-	if err := os.WriteFile(cfgPath, data, 0o644); err != nil {
+	fmt.Printf("Config written to %s (%d device(s) added)\n", cfgPath, added)
-		return fmt.Errorf("writing config: %w", err)
-	}
-
-	fmt.Printf("Config written to %s\n", cfgPath)
 	return nil
 }
 
@@ -101,13 +108,3 @@ func isRootBacking(path dbus.ObjectPath, rootDevices []dbus.ObjectPath) bool {
 	}
 	return false
 }
-
-func aliasFromUUID(uuid string) string {
-	// Use first 8 chars of UUID as a stable alias.
-	// "b8b2f8e3-4cde-4aca-a96e-df9274019f9f" -> "b8b2f8e3"
-	clean := strings.ReplaceAll(uuid, "-", "")
-	if len(clean) > 8 {
-		clean = clean[:8]
-	}
-	return clean
-}

cmd/mount.go

@@ -19,6 +19,7 @@ var mountCmd = &cobra.Command{
 	Short:             "Unlock and mount a LUKS volume",
 	Args:              cobra.ExactArgs(1),
 	RunE:              runMount,
+	ValidArgsFunction: completeDeviceOrAlias,
 }
 
 func init() {

cmd/root.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 
+	"git.wntrmute.dev/kyle/arca/internal/verbose"
 	"github.com/spf13/cobra"
 )
 
@@ -12,6 +13,10 @@ var rootCmd = &cobra.Command{
 	Short: "Mount and unmount LUKS-encrypted volumes",
 }
 
+func init() {
+	rootCmd.PersistentFlags().BoolVarP(&verbose.Enabled, "verbose", "v", false, "print debug information to stderr")
+}
+
 func SetVersion(v string) {
 	rootCmd.Version = v
 }

cmd/unmount.go

@@ -15,6 +15,7 @@ var unmountCmd = &cobra.Command{
 	Short:             "Unmount and lock a LUKS volume",
 	Args:              cobra.ExactArgs(1),
 	RunE:              runUnmount,
+	ValidArgsFunction: completeDeviceOrAlias,
 }
 
 func init() {

flake.nix

@@ -10,7 +10,7 @@
     let
       system = "x86_64-linux";
       pkgs = nixpkgs.legacyPackages.${system};
-      version = "1.0.0";
+      version = "1.2.0";
     in
     {
       packages.${system}.default = pkgs.buildGoModule {
@@ -21,6 +21,14 @@
         ldflags = [
           "-X main.version=${version}"
         ];
+        postInstall = ''
+          mkdir -p $out/share/zsh/site-functions
+          mkdir -p $out/share/bash-completion/completions
+          mkdir -p $out/share/fish/vendor_completions.d
+          $out/bin/arca completion zsh > $out/share/zsh/site-functions/_arca
+          $out/bin/arca completion bash > $out/share/bash-completion/completions/arca
+          $out/bin/arca completion fish > $out/share/fish/vendor_completions.d/arca.fish
+        '';
       };
     };
 }

internal/config/config.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
 
@@ -76,6 +77,31 @@ func resolvedFrom(dev DeviceConfig) ResolvedDevice {
 	}
 }
 
+// HasUUID returns true if a device with the given UUID is already configured.
+func (c *Config) HasUUID(uuid string) bool {
+	for _, dev := range c.Devices {
+		if dev.UUID == uuid {
+			return true
+		}
+	}
+	return false
+}
+
+// Save writes the config to the config file.
+func (c *Config) Save() error {
+	path := configPath()
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		return fmt.Errorf("creating config directory: %w", err)
+	}
+
+	data, err := yaml.Marshal(c)
+	if err != nil {
+		return fmt.Errorf("marshaling config: %w", err)
+	}
+
+	return os.WriteFile(path, data, 0o644)
+}
+
 // AliasFor returns the config alias for a given UUID, or "" if none.
 func (c *Config) AliasFor(uuid string) string {
 	for name, dev := range c.Devices {

internal/cryptsetup/cryptsetup.go

@@ -5,6 +5,9 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strings"
+
+	"git.wntrmute.dev/kyle/arca/internal/verbose"
 )
 
 // Open opens a LUKS device using cryptsetup with token-based unlock.
@@ -12,6 +15,8 @@ func Open(devicePath, mapperName string) error {
 	args := withTokenPluginEnv([]string{"cryptsetup", "open", devicePath, mapperName, "--token-only"})
 	args = withPrivilege(args)
 
+	verbose.Printf("exec: %s", strings.Join(args, " "))
+
 	cmd := exec.Command(args[0], args[1:]...)
 	cmd.Stdin = os.Stdin
 	cmd.Stdout = os.Stdout
@@ -59,7 +64,8 @@ func Mount(devicePath, mountpoint string) (string, error) {
 	return mountpoint, nil
 }
 
-// Unmount unmounts the given mountpoint using privileged umount.
+// Unmount unmounts the given mountpoint using privileged umount, then
+// removes the mount directory if it is empty.
 func Unmount(mountpoint string) error {
 	args := withPrivilege([]string{"umount", mountpoint})
 	cmd := exec.Command(args[0], args[1:]...)
@@ -68,6 +74,12 @@ func Unmount(mountpoint string) error {
 	if err := cmd.Run(); err != nil {
 		return fmt.Errorf("umount %s: %w", mountpoint, err)
 	}
+
+	// Clean up empty mount directory. Best-effort — ignore errors
+	// (directory may not be empty or may be a system path).
+	rmdirArgs := withPrivilege([]string{"rmdir", mountpoint})
+	exec.Command(rmdirArgs[0], rmdirArgs[1:]...).Run()
+
 	return nil
 }
 
@@ -101,6 +113,7 @@ func findTokenPluginDir() string {
 	// NixOS stable symlink — survives rebuilds.
 	const nixSystemPath = "/run/current-system/sw/lib/cryptsetup"
 	if hasTokenPlugins(nixSystemPath) {
+		verbose.Printf("token plugin dir: %s", nixSystemPath)
 		return nixSystemPath
 	}
 
@@ -109,11 +122,13 @@ func findTokenPluginDir() string {
 		if resolved, err := filepath.EvalSymlinks(bin); err == nil {
 			dir := filepath.Join(filepath.Dir(filepath.Dir(resolved)), "lib", "cryptsetup")
 			if hasTokenPlugins(dir) {
+				verbose.Printf("token plugin dir (from systemd-cryptenroll): %s", dir)
 				return dir
 			}
 		}
 	}
 
+	verbose.Printf("no token plugin directory found")
 	return ""
 }
 

internal/udisks/client.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 
+	"git.wntrmute.dev/kyle/arca/internal/verbose"
 	"github.com/godbus/dbus/v5"
 )
 
@@ -18,6 +19,7 @@ func NewClient() (*Client, error) {
 	if err != nil {
 		return nil, fmt.Errorf("cannot connect to udisks2 — is the udisks2 service running? (%w)", err)
 	}
+	verbose.Printf("connected to system D-Bus")
 	return &Client{conn: conn}, nil
 }
 

internal/unlock/unlock.go

@@ -8,6 +8,7 @@ import (
 
 	"git.wntrmute.dev/kyle/arca/internal/cryptsetup"
 	"git.wntrmute.dev/kyle/arca/internal/udisks"
+	"git.wntrmute.dev/kyle/arca/internal/verbose"
 )
 
 // Result holds the outcome of a successful unlock.
@@ -35,12 +36,16 @@ func New(client *udisks.Client, opts Options) *Unlocker {
 
 // Unlock tries each method in order and returns the result on first success.
 func (u *Unlocker) Unlock(dev *udisks.BlockDevice, methods []string) (*Result, error) {
+	verbose.Printf("unlock %s: methods %v", dev.DevicePath, methods)
 	var errs []error
 	for _, method := range methods {
+		verbose.Printf("trying method: %s", method)
 		res, err := u.tryMethod(dev, method)
 		if err == nil {
+			verbose.Printf("method %s succeeded", method)
 			return res, nil
 		}
+		verbose.Printf("method %s failed: %v", method, err)
 		errs = append(errs, fmt.Errorf("%s: %w", method, err))
 	}
 	return nil, fmt.Errorf("all unlock methods failed for %s:\n%w", dev.DevicePath, errors.Join(errs...))

internal/verbose/verbose.go

@@ -0,0 +1,16 @@
+package verbose
+
+import (
+	"fmt"
+	"os"
+)
+
+// Enabled is set by the root command's --verbose flag.
+var Enabled bool
+
+// Printf prints to stderr if verbose mode is enabled.
+func Printf(format string, args ...any) {
+	if Enabled {
+		fmt.Fprintf(os.Stderr, "arca: "+format+"\n", args...)
+	}
+}