Improve PGP unlocker ergonomics

- Support 'secret unlockers add pgp [keyid]' positional argument syntax
- Automatically detect and use default GPG key when no key is specified
- Change PGP unlocker ID format from <keyid>-pgp to pgp-<keyid>
- Check if PGP key is already added before creating duplicate unlocker
- Add getDefaultGPGKey() that checks gpgconf first, then falls back to
  first secret key
- Export ResolveGPGKeyFingerprint() for use in CLI
- Add checkUnlockerExists() helper to verify unlocker IDs

The new behavior:
- 'secret unlockers add pgp' uses default GPG key
- 'secret unlockers add pgp KEYID' uses specified key
- 'secret unlockers add pgp --keyid=KEYID' also works
- Errors if key is already added or no default key exists

internal/cli/unlockers.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"strings"
 	"time"
@@ -15,9 +16,44 @@ import (
 	"github.com/spf13/cobra"
 )
 
-// Import from init.go
+// getDefaultGPGKey returns the default GPG key ID if available
+func getDefaultGPGKey() (string, error) {
+	// First try to get the configured default key using gpgconf
+	cmd := exec.Command("gpgconf", "--list-options", "gpg")
+	output, err := cmd.Output()
+	if err == nil {
+		lines := strings.Split(string(output), "\n")
+		for _, line := range lines {
+			fields := strings.Split(line, ":")
+			if len(fields) > 9 && fields[0] == "default-key" && fields[9] != "" {
+				// The default key is in field 10 (index 9)
+				return fields[9], nil
+			}
+		}
+	}
 
-// ... existing imports ...
+	// If no default key is configured, get the first secret key
+	cmd = exec.Command("gpg", "--list-secret-keys", "--with-colons")
+	output, err = cmd.Output()
+	if err != nil {
+		return "", fmt.Errorf("failed to list GPG keys: %w", err)
+	}
+
+	// Parse output to find the first usable secret key
+	lines := strings.Split(string(output), "\n")
+	for _, line := range lines {
+		// sec line indicates a secret key
+		if strings.HasPrefix(line, "sec:") {
+			fields := strings.Split(line, ":")
+			// Field 5 contains the key ID
+			if len(fields) > 4 && fields[4] != "" {
+				return fields[4], nil
+			}
+		}
+	}
+
+	return "", fmt.Errorf("no GPG secret keys found")
+}
 
 func newUnlockersCmd() *cobra.Command {
 	cmd := &cobra.Command{
@@ -55,13 +91,19 @@ func newUnlockersListCmd() *cobra.Command {
 
 func newUnlockersAddCmd() *cobra.Command {
 	cmd := &cobra.Command{
-		Use:   "add <type>",
+		Use:   "add <type> [keyid]",
 		Short: "Add a new unlocker",
 		Long:  `Add a new unlocker of the specified type (passphrase, keychain, pgp).`,
-		Args:  cobra.ExactArgs(1),
+		Args:  cobra.RangeArgs(1, 2), //nolint:mnd // Command accepts 1 or 2 arguments
 		RunE: func(cmd *cobra.Command, args []string) error {
 			cli := NewCLIInstance()
 
+			// For PGP type, check if keyid is provided as positional argument
+			if args[0] == "pgp" && len(args) == 2 {
+				// Override any flag value with the positional argument
+				_ = cmd.Flags().Set("keyid", args[1])
+			}
+
 			return cli.UnlockersAdd(args[0], cmd)
 		},
 	}
@@ -300,14 +342,38 @@ func (cli *Instance) UnlockersAdd(unlockerType string, cmd *cobra.Command) error
 		return nil
 
 	case "pgp":
-		// Get GPG key ID from flag or environment variable
+		// Get GPG key ID from flag, environment, or default key
 		var gpgKeyID string
 		if flagKeyID, _ := cmd.Flags().GetString("keyid"); flagKeyID != "" {
 			gpgKeyID = flagKeyID
 		} else if envKeyID := os.Getenv(secret.EnvGPGKeyID); envKeyID != "" {
 			gpgKeyID = envKeyID
 		} else {
-			return fmt.Errorf("GPG key ID required: use --keyid flag or set SB_GPG_KEY_ID environment variable")
+			// Try to get the default GPG key
+			defaultKeyID, err := getDefaultGPGKey()
+			if err != nil {
+				return fmt.Errorf("no GPG key specified and no default key found: %w", err)
+			}
+			gpgKeyID = defaultKeyID
+			cmd.Printf("Using default GPG key: %s\n", gpgKeyID)
+		}
+
+		// Check if this key is already added as an unlocker
+		vlt, err := vault.GetCurrentVault(cli.fs, cli.stateDir)
+		if err != nil {
+			return fmt.Errorf("failed to get current vault: %w", err)
+		}
+
+		// Resolve the GPG key ID to its fingerprint
+		fingerprint, err := secret.ResolveGPGKeyFingerprint(gpgKeyID)
+		if err != nil {
+			return fmt.Errorf("failed to resolve GPG key fingerprint: %w", err)
+		}
+
+		// Check if this GPG key is already added
+		expectedID := fmt.Sprintf("pgp-%s", fingerprint)
+		if err := cli.checkUnlockerExists(vlt, expectedID); err != nil {
+			return fmt.Errorf("GPG key %s is already added as an unlocker", gpgKeyID)
 		}
 
 		pgpUnlocker, err := secret.CreatePGPUnlocker(cli.fs, cli.stateDir, gpgKeyID)
@@ -380,3 +446,69 @@ func (cli *Instance) UnlockerSelect(unlockerID string) error {
 
 	return vlt.SelectUnlocker(unlockerID)
 }
+
+// checkUnlockerExists checks if an unlocker with the given ID exists
+func (cli *Instance) checkUnlockerExists(vlt *vault.Vault, unlockerID string) error {
+	// Get the list of unlockers and check if any match the ID
+	unlockers, err := vlt.ListUnlockers()
+	if err != nil {
+		return nil // If we can't list unlockers, assume it doesn't exist
+	}
+
+	// Get vault directory to construct unlocker instances
+	vaultDir, err := vlt.GetDirectory()
+	if err != nil {
+		return nil
+	}
+
+	// Check each unlocker's ID
+	for _, metadata := range unlockers {
+		// Construct the unlocker based on type to get its ID
+		unlockersDir := filepath.Join(vaultDir, "unlockers.d")
+		files, err := afero.ReadDir(cli.fs, unlockersDir)
+		if err != nil {
+			continue
+		}
+
+		for _, file := range files {
+			if !file.IsDir() {
+				continue
+			}
+
+			unlockerDir := filepath.Join(unlockersDir, file.Name())
+			metadataPath := filepath.Join(unlockerDir, "unlocker-metadata.json")
+
+			// Check if this matches our metadata
+			metadataBytes, err := afero.ReadFile(cli.fs, metadataPath)
+			if err != nil {
+				continue
+			}
+
+			var diskMetadata secret.UnlockerMetadata
+			if err := json.Unmarshal(metadataBytes, &diskMetadata); err != nil {
+				continue
+			}
+
+			// Match by type and creation time
+			if diskMetadata.Type == metadata.Type && diskMetadata.CreatedAt.Equal(metadata.CreatedAt) {
+				var unlocker secret.Unlocker
+				switch metadata.Type {
+				case "passphrase":
+					unlocker = secret.NewPassphraseUnlocker(cli.fs, unlockerDir, diskMetadata)
+				case "keychain":
+					unlocker = secret.NewKeychainUnlocker(cli.fs, unlockerDir, diskMetadata)
+				case "pgp":
+					unlocker = secret.NewPGPUnlocker(cli.fs, unlockerDir, diskMetadata)
+				}
+
+				if unlocker != nil && unlocker.GetID() == unlockerID {
+					return fmt.Errorf("unlocker already exists")
+				}
+
+				break
+			}
+		}
+	}
+
+	return nil
+}

internal/secret/pgpunlocker.go

@@ -128,7 +128,7 @@ func (p *PGPUnlocker) GetDirectory() string {
 
 // GetID implements Unlocker interface - generates ID from GPG key ID
 func (p *PGPUnlocker) GetID() string {
-	// Generate ID using GPG key ID: <keyid>-pgp
+	// Generate ID using GPG key ID: pgp-<keyid>
 	gpgKeyID, err := p.GetGPGKeyID()
 	if err != nil {
 		// The vault metadata is corrupt - this is a fatal error
@@ -136,7 +136,7 @@ func (p *PGPUnlocker) GetID() string {
 		panic(fmt.Sprintf("PGP unlocker metadata is corrupt or missing GPG key ID: %v", err))
 	}
 
-	return fmt.Sprintf("%s-pgp", gpgKeyID)
+	return fmt.Sprintf("pgp-%s", gpgKeyID)
 }
 
 // Remove implements Unlocker interface - removes the PGP unlocker
@@ -267,7 +267,7 @@ func CreatePGPUnlocker(fs afero.Fs, stateDir string, gpgKeyID string) (*PGPUnloc
 	}
 
 	// Step 9: Resolve the GPG key ID to its full fingerprint
-	fingerprint, err := resolveGPGKeyFingerprint(gpgKeyID)
+	fingerprint, err := ResolveGPGKeyFingerprint(gpgKeyID)
 	if err != nil {
 		return nil, fmt.Errorf("failed to resolve GPG key fingerprint: %w", err)
 	}
@@ -313,8 +313,8 @@ func validateGPGKeyID(keyID string) error {
 	return nil
 }
 
-// resolveGPGKeyFingerprint resolves any GPG key identifier to its full fingerprint
+// ResolveGPGKeyFingerprint resolves any GPG key identifier to its full fingerprint
-func resolveGPGKeyFingerprint(keyID string) (string, error) {
+func ResolveGPGKeyFingerprint(keyID string) (string, error) {
 	if err := validateGPGKeyID(keyID); err != nil {
 		return "", fmt.Errorf("invalid GPG key ID: %w", err)
 	}