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. errUnsupportedUnlockerType is removed for
errInvalidUnlockerType, which names the same failure. 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