Give each failure one error value (closes #113)

internal/cli's copies of vault.ErrSecretNotFound, ErrVaultNotFound,
ErrVersionNotFound and ErrSecretExists are removed; the commands wrap the
vault errors. Every error of secret.ReadPassphrase wraps
ErrPassphraseNotRead, so its callers no longer add those words.
ResolveGPGKeyFingerprint returns ErrGPGKeyNotFound for a key the keyring
lacks, recognised by gpg's status line. storeInKeychain returns
errNilDataBuffer. bip85's ErrPasswordTooShort and ErrEncodedTooShort go
with their unreachable checks. Tests that matched these errors' text use
errors.Is.

Model: opus-5-5

internal/cli/secrets.go

@@ -35,10 +35,6 @@ var (
 	errSecretTooLarge     = errors.New("secret too large: exceeds 100MB limit")
 	errSecretFileTooLarge = errors.New(
 		"secret file too large: exceeds 100MB limit")
-	errSecretNotFound      = errors.New("not found")
-	errSecretExistsNoForce = errors.New(
-		"already exists (use --force to overwrite)")
-	errVaultDoesNotExist           = errors.New("does not exist")
 	errCrossVaultSourceUnqualified = errors.New(
 		"source must specify vault (e.g., vault:secret) for cross-vault move")
 	errMoveOntoItself = errors.New("cannot be moved onto itself")
@@ -776,7 +772,7 @@ func (cli *Instance) findSecretToRemove(
 
 	if !exists {
 		return secretToRemove{},
-			fmt.Errorf("secret '%s' %w", secretName, errSecretNotFound)
+			fmt.Errorf("secret '%s' %w", secretName, vault.ErrSecretNotFound)
 	}
 
 	// A secret without a versions directory has no versions, and can
@@ -907,7 +903,7 @@ func (cli *Instance) existingVault(name string) (*vault.Vault, error) {
 	}
 
 	if !slices.Contains(vaults, name) {
-		return nil, fmt.Errorf("vault '%s' %w", name, errVaultDoesNotExist)
+		return nil, fmt.Errorf("vault '%s' %w", name, vault.ErrVaultNotFound)
 	}
 
 	return vault.NewVault(cli.fs, cli.stateDir, name), nil
@@ -938,7 +934,7 @@ func (cli *Instance) moveSecretWithinVault(
 	}
 
 	if !exists {
-		return fmt.Errorf("secret '%s' %w", source, errSecretNotFound)
+		return fmt.Errorf("secret '%s' %w", source, vault.ErrSecretNotFound)
 	}
 
 	destEncoded := strings.ReplaceAll(dest, "/", "%")
@@ -963,7 +959,8 @@ func (cli *Instance) moveSecretWithinVault(
 
 	if exists {
 		if !force {
-			return fmt.Errorf("secret '%s' %w", dest, errSecretExistsNoForce)
+			return fmt.Errorf("secret '%s' %w (use --force to overwrite)",
+				dest, vault.ErrSecretExists)
 		}
 
 		err = secret.RemoveDirAtomic(cli.fs, destDir)
@@ -1028,7 +1025,7 @@ func (cli *Instance) moveSecretCrossVault(
 	exists, err := afero.DirExists(cli.fs, srcSecretDir)
 	if err != nil || !exists {
 		return fmt.Errorf("secret '%s' %w in vault '%s'",
-			srcSecretName, errSecretNotFound, srcVault.Name)
+			srcSecretName, vault.ErrSecretNotFound, srcVault.Name)
 	}
 
 	// The source is removed after the copy, so a destination that is the