Local-first runtime cleanup and recovery hardening

internal/localdb/encryption.go

@@ -7,19 +7,104 @@ import (
 	"crypto/sha256"
 	"encoding/base64"
 	"errors"
+	"fmt"
 	"io"
 	"os"
+	"path/filepath"
+	"strings"
+
+	"git.mchus.pro/mchus/quoteforge/internal/appstate"
 )
 
-// getEncryptionKey derives a 32-byte key from environment variable or machine ID
-func getEncryptionKey() []byte {
+const encryptionKeyFileName = "local_encryption.key"
+
+// getEncryptionKey resolves the active encryption key.
+// Preference order:
+// 1. QUOTEFORGE_ENCRYPTION_KEY env var
+// 2. application-managed random key file in the user state directory
+func getEncryptionKey() ([]byte, error) {
 	key := os.Getenv("QUOTEFORGE_ENCRYPTION_KEY")
-	if key == "" {
-		// Fallback to a machine-based key (hostname + fixed salt)
-		hostname, _ := os.Hostname()
-		key = hostname + "quoteforge-salt-2024"
+	if key != "" {
+		hash := sha256.Sum256([]byte(key))
+		return hash[:], nil
 	}
-	// Hash to get exactly 32 bytes for AES-256
+
+	stateDir, err := resolveEncryptionStateDir()
+	if err != nil {
+		return nil, fmt.Errorf("resolve encryption state dir: %w", err)
+	}
+
+	return loadOrCreateEncryptionKey(filepath.Join(stateDir, encryptionKeyFileName))
+}
+
+func resolveEncryptionStateDir() (string, error) {
+	configPath, err := appstate.ResolveConfigPath("")
+	if err != nil {
+		return "", err
+	}
+	return filepath.Dir(configPath), nil
+}
+
+func loadOrCreateEncryptionKey(path string) ([]byte, error) {
+	if data, err := os.ReadFile(path); err == nil {
+		return parseEncryptionKeyFile(data)
+	} else if !errors.Is(err, os.ErrNotExist) {
+		return nil, fmt.Errorf("read encryption key: %w", err)
+	}
+
+	if err := os.MkdirAll(filepath.Dir(path), 0700); err != nil {
+		return nil, fmt.Errorf("create encryption key dir: %w", err)
+	}
+
+	raw := make([]byte, 32)
+	if _, err := io.ReadFull(rand.Reader, raw); err != nil {
+		return nil, fmt.Errorf("generate encryption key: %w", err)
+	}
+
+	encoded := base64.StdEncoding.EncodeToString(raw)
+	if err := writeKeyFile(path, []byte(encoded+"\n")); err != nil {
+		if errors.Is(err, os.ErrExist) {
+			data, readErr := os.ReadFile(path)
+			if readErr != nil {
+				return nil, fmt.Errorf("read concurrent encryption key: %w", readErr)
+			}
+			return parseEncryptionKeyFile(data)
+		}
+		return nil, err
+	}
+
+	return raw, nil
+}
+
+func writeKeyFile(path string, data []byte) error {
+	file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0600)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	if _, err := file.Write(data); err != nil {
+		return err
+	}
+
+	return file.Sync()
+}
+
+func parseEncryptionKeyFile(data []byte) ([]byte, error) {
+	trimmed := strings.TrimSpace(string(data))
+	decoded, err := base64.StdEncoding.DecodeString(trimmed)
+	if err != nil {
+		return nil, fmt.Errorf("decode encryption key file: %w", err)
+	}
+	if len(decoded) != 32 {
+		return nil, fmt.Errorf("invalid encryption key length: %d", len(decoded))
+	}
+	return decoded, nil
+}
+
+func getLegacyEncryptionKey() []byte {
+	hostname, _ := os.Hostname()
+	key := hostname + "quoteforge-salt-2024"
 	hash := sha256.Sum256([]byte(key))
 	return hash[:]
 }
@@ -30,7 +115,10 @@ func Encrypt(plaintext string) (string, error) {
 		return "", nil
 	}
 
-	key := getEncryptionKey()
+	key, err := getEncryptionKey()
+	if err != nil {
+		return "", err
+	}
 	block, err := aes.NewCipher(key)
 	if err != nil {
 		return "", err
@@ -56,12 +144,50 @@ func Decrypt(ciphertext string) (string, error) {
 		return "", nil
 	}
 
-	key := getEncryptionKey()
-	data, err := base64.StdEncoding.DecodeString(ciphertext)
+	key, err := getEncryptionKey()
 	if err != nil {
 		return "", err
 	}
+	plaintext, legacy, err := decryptWithKeys(ciphertext, key, getLegacyEncryptionKey())
+	if err != nil {
+		return "", err
+	}
+	_ = legacy
+	return plaintext, nil
+}
 
+func DecryptWithMetadata(ciphertext string) (string, bool, error) {
+	if ciphertext == "" {
+		return "", false, nil
+	}
+
+	key, err := getEncryptionKey()
+	if err != nil {
+		return "", false, err
+	}
+	return decryptWithKeys(ciphertext, key, getLegacyEncryptionKey())
+}
+
+func decryptWithKeys(ciphertext string, primaryKey, legacyKey []byte) (string, bool, error) {
+	data, err := base64.StdEncoding.DecodeString(ciphertext)
+	if err != nil {
+		return "", false, err
+	}
+
+	plaintext, err := decryptWithKey(data, primaryKey)
+	if err == nil {
+		return plaintext, false, nil
+	}
+
+	legacyPlaintext, legacyErr := decryptWithKey(data, legacyKey)
+	if legacyErr == nil {
+		return legacyPlaintext, true, nil
+	}
+
+	return "", false, err
+}
+
+func decryptWithKey(data, key []byte) (string, error) {
 	block, err := aes.NewCipher(key)
 	if err != nil {
 		return "", err