Update golangci-lint to v2.12.2 with canonical config

- Replace .golangci.yml with the canonical strict config (all linters
  enabled except the standard disable list; lll 88, funlen 80/50,
  cyclop 15, dupl 100; test files now linted)
- Pin the Dockerfile lint stage to golangci/golangci-lint:v2.12.2 by
  tag and digest (Debian-based)
- Fix all ~1550 findings surfaced by the new config: line wrapping,
  wsl_v5/nlreturn blank lines, noinlineerr splits, err113 sentinel
  errors, perfsprint/modernize rewrites, goconst constants, thelper,
  testifylint, noctx CommandContext, testpackage conversions,
  t.Parallel() where safe, and complexity/dupl helper extraction
- Record the change and follow-up items in TODO.md

internal/cli/generate.go

@@ -2,6 +2,7 @@ package cli
 
 import (
 	"crypto/rand"
+	"errors"
 	"fmt"
 	"math/big"
 	"os"
@@ -17,6 +18,16 @@ const (
 	mnemonicEntropyBits = 128
 )
 
+// Sentinel errors for secret generation
+var (
+	errLengthTooSmall           = errors.New("length must be at least 1")
+	errLengthNotPositive        = errors.New("length must be positive")
+	errMnemonicTypeNotSupported = errors.New(
+		"mnemonic type not supported for secret generation, " +
+			"use 'secret generate mnemonic' instead")
+	errUnsupportedSecretType = errors.New("unsupported type")
+)
+
 func newGenerateCmd() *cobra.Command {
 	cmd := &cobra.Command{
 		Use:   "generate",
@@ -52,8 +63,9 @@ func newGenerateSecretCmd() *cobra.Command {
 	cmd := &cobra.Command{
 		Use:   "secret <name>",
 		Short: "Generate a random secret and store it in the vault",
-		Long:  `Generate a cryptographically secure random secret and store it in the current vault under the given name.`,
-		Args:  cobra.ExactArgs(1),
+		Long: `Generate a cryptographically secure random secret and ` +
+			`store it in the current vault under the given name.`,
+		Args: cobra.ExactArgs(1),
 		RunE: func(cmd *cobra.Command, args []string) error {
 			length, _ := cmd.Flags().GetInt("length")
 			secretType, _ := cmd.Flags().GetString("type")
@@ -68,8 +80,10 @@ func newGenerateSecretCmd() *cobra.Command {
 		},
 	}
 
-	cmd.Flags().IntP("length", "l", defaultSecretLength, "Length of the generated secret (default 16)")
-	cmd.Flags().StringP("type", "t", "base58", "Type of secret to generate (base58, alnum)")
+	cmd.Flags().IntP("length", "l", defaultSecretLength,
+		"Length of the generated secret (default 16)")
+	cmd.Flags().StringP("type", "t", "base58",
+		"Type of secret to generate (base58, alnum)")
 	cmd.Flags().BoolP("force", "f", false, "Overwrite existing secret")
 
 	return cmd
@@ -98,7 +112,8 @@ func (cli *Instance) GenerateMnemonic(cmd *cobra.Command) error {
 	fmt.Fprintln(os.Stderr, "   • Write it down on paper and store it safely")
 	fmt.Fprintln(os.Stderr, "   • Do not store it digitally or share it with anyone")
 	fmt.Fprintln(os.Stderr, "   • You will need this phrase to recover your secrets")
-	fmt.Fprintln(os.Stderr, "   • If you lose this phrase, your secrets cannot be recovered")
+	fmt.Fprintln(os.Stderr,
+		"   • If you lose this phrase, your secrets cannot be recovered")
 	fmt.Fprintln(os.Stderr, "")
 	fmt.Fprintln(os.Stderr, "Use this mnemonic with:")
 	fmt.Fprintln(os.Stderr, "   secret init    (to initialize a new secret manager)")
@@ -116,11 +131,13 @@ func (cli *Instance) GenerateSecret(
 	force bool,
 ) error {
 	if length < 1 {
-		return fmt.Errorf("length must be at least 1")
+		return errLengthTooSmall
 	}
 
-	var secretValue string
-	var err error
+	var (
+		secretValue string
+		err         error
+	)
 
 	switch secretType {
 	case "base58":
@@ -128,9 +145,10 @@ func (cli *Instance) GenerateSecret(
 	case "alnum":
 		secretValue, err = generateRandomAlnum(length)
 	case "mnemonic":
-		return fmt.Errorf("mnemonic type not supported for secret generation, use 'secret generate mnemonic' instead")
+		return errMnemonicTypeNotSupported
 	default:
-		return fmt.Errorf("unsupported type: %s (supported: base58, alnum)", secretType)
+		return fmt.Errorf("%w: %s (supported: base58, alnum)",
+			errUnsupportedSecretType, secretType)
 	}
 
 	if err != nil {
@@ -147,11 +165,13 @@ func (cli *Instance) GenerateSecret(
 	secretBuffer := memguard.NewBufferFromBytes([]byte(secretValue))
 	defer secretBuffer.Destroy()
 
-	if err := vlt.AddSecret(secretName, secretBuffer, force); err != nil {
+	err = vlt.AddSecret(secretName, secretBuffer, force)
+	if err != nil {
 		return err
 	}
 
-	cmd.Printf("Generated and stored %d-character %s secret: %s\n", length, secretType, secretName)
+	cmd.Printf("Generated and stored %d-character %s secret: %s\n",
+		length, secretType, secretName)
 
 	return nil
 }
@@ -170,10 +190,11 @@ func generateRandomAlnum(length int) (string, error) {
 	return generateRandomString(length, alnumChars)
 }
 
-// generateRandomString generates a random string of the specified length using the given character set
+// generateRandomString generates a random string of the specified length
+// using the given character set
 func generateRandomString(length int, charset string) (string, error) {
 	if length <= 0 {
-		return "", fmt.Errorf("length must be positive")
+		return "", errLengthNotPositive
 	}
 
 	result := make([]byte, length)
@@ -184,6 +205,7 @@ func generateRandomString(length int, charset string) (string, error) {
 		if err != nil {
 			return "", fmt.Errorf("failed to generate random number: %w", err)
 		}
+
 		result[i] = charset[randomIndex.Int64()]
 	}