Add send-log retention days to panel Settings.

Global administrators can set delivery journal retention (7-365 days) in SQLite;
SEND_LOG_RETENTION_DAYS seeds the initial default and the log-tailer re-reads
the value every prune cycle without a restart.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/store/settings.go

@@ -4,8 +4,79 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"strconv"
 )
 
+const (
+	// SendLogRetentionDaysKey is the settings table key for delivery-journal
+	// retention (architecture.md § Persistence).
+	SendLogRetentionDaysKey = "send_log_retention_days"
+	SendLogRetentionDaysMin = 7
+	SendLogRetentionDaysMax = 365
+	// SendLogRetentionDaysDefault matches SEND_LOG_RETENTION_DAYS when unset.
+	SendLogRetentionDaysDefault = 90
+)
+
+// ErrSendLogRetentionDaysOutOfRange is returned when retention is outside the
+// allowed panel range.
+var ErrSendLogRetentionDaysOutOfRange = errors.New("send log retention days out of range")
+
+// ValidateSendLogRetentionDays checks the panel-allowed retention window.
+func ValidateSendLogRetentionDays(days int) error {
+	if days < SendLogRetentionDaysMin || days > SendLogRetentionDaysMax {
+		return fmt.Errorf("%w: must be between %d and %d days", ErrSendLogRetentionDaysOutOfRange, SendLogRetentionDaysMin, SendLogRetentionDaysMax)
+	}
+	return nil
+}
+
+func sendLogRetentionFallback(envDefault int) int {
+	if envDefault > 0 {
+		if err := ValidateSendLogRetentionDays(envDefault); err == nil {
+			return envDefault
+		}
+	}
+	return SendLogRetentionDaysDefault
+}
+
+// GetSendLogRetentionDays returns the effective retention window. When the
+// setting is missing or invalid, envDefault is used (guide § Environment
+// variables: SEND_LOG_RETENTION_DAYS).
+func (s *Store) GetSendLogRetentionDays(envDefault int) (int, error) {
+	raw, err := s.GetSetting(SendLogRetentionDaysKey)
+	if err != nil {
+		return 0, err
+	}
+	if raw == "" {
+		return sendLogRetentionFallback(envDefault), nil
+	}
+	days, err := strconv.Atoi(raw)
+	if err != nil || ValidateSendLogRetentionDays(days) != nil {
+		return sendLogRetentionFallback(envDefault), nil
+	}
+	return days, nil
+}
+
+// SetSendLogRetentionDays persists the panel-configured retention window.
+func (s *Store) SetSendLogRetentionDays(days int) error {
+	if err := ValidateSendLogRetentionDays(days); err != nil {
+		return err
+	}
+	return s.SetSetting(SendLogRetentionDaysKey, strconv.Itoa(days))
+}
+
+// EnsureSendLogRetentionDays seeds the setting from envDefault when it has
+// never been written (first panel start after upgrade).
+func (s *Store) EnsureSendLogRetentionDays(envDefault int) error {
+	raw, err := s.GetSetting(SendLogRetentionDaysKey)
+	if err != nil {
+		return err
+	}
+	if raw != "" {
+		return nil
+	}
+	return s.SetSendLogRetentionDays(sendLogRetentionFallback(envDefault))
+}
+
 // GetSetting returns a settings value or empty string when missing.
 func (s *Store) GetSetting(key string) (string, error) {
 	var value string