release: 1.6.0: 30-day send stats and optional auto level-2 rate limits

30-day sending statistics per domain and application, plus optional auto level-2 rate limits derived from average send rate.
Added:
  - Domain page **Sending statistics** card: total messages, peak and average
  - Level-2 rate limit **Manual** / **Auto** mode on domain and application
  - Domain export JSON now includes rate limits (`mode`, `auto_multiplier`,
Changed:
  - Auto mode uses the level-1 window (`RATE_LIMIT_WINDOW_SECONDS`); manual

Full detail: CHANGELOG.md (1.6.0).

internal/store/stats.go

@@ -0,0 +1,101 @@
+package store
+
+import (
+	"fmt"
+	"math"
+	"time"
+)
+
+// StatsWindowDays is the rolling window for send statistics on the domain page.
+const StatsWindowDays = 30
+
+// SendStats holds message-volume metrics over a stats window (guide § Rate
+// limiting — same counting rules as CountMessages).
+type SendStats struct {
+	Total       int64
+	PeakPerHour int64
+	AvgPerHour  float64
+	WindowDays  int   // actual days queried (min(30, retention))
+	WindowHours float64 // hours used for the average-rate denominator
+}
+
+// StatsWindow computes the since timestamp and hours denominator for send
+// statistics. The query window is min(30, retention) days; hours_in_window is
+// min(720, entity age in hours, retention hours).
+func StatsWindow(retentionDays int, entityCreated time.Time) (since time.Time, hours float64, windowDays int) {
+	if retentionDays <= 0 {
+		retentionDays = SendLogRetentionDaysDefault
+	}
+	windowDays = StatsWindowDays
+	if retentionDays < StatsWindowDays {
+		windowDays = retentionDays
+	}
+	since = time.Now().UTC().AddDate(0, 0, -windowDays)
+
+	retentionHours := float64(retentionDays) * 24
+	ageHours := time.Since(entityCreated).Hours()
+	if ageHours < 0 {
+		ageHours = 0
+	}
+
+	hours = math.Min(720, math.Min(ageHours, retentionHours))
+	if hours < 1 {
+		hours = 1
+	}
+	return since, hours, windowDays
+}
+
+// DomainSendStats returns 30-day (or shorter when retention is lower) send
+// statistics for a domain name.
+func (s *Store) DomainSendStats(name string, retentionDays int, createdAt time.Time) (SendStats, error) {
+	since, hours, windowDays := StatsWindow(retentionDays, createdAt)
+	stats, err := s.sendStats("domain", name, since, hours)
+	if err != nil {
+		return SendStats{}, err
+	}
+	stats.WindowDays = windowDays
+	stats.WindowHours = hours
+	return stats, nil
+}
+
+// AppSendStats returns send statistics for an application login.
+func (s *Store) AppSendStats(login string, retentionDays int, createdAt time.Time) (SendStats, error) {
+	since, hours, windowDays := StatsWindow(retentionDays, createdAt)
+	stats, err := s.sendStats("app_login", login, since, hours)
+	if err != nil {
+		return SendStats{}, err
+	}
+	stats.WindowDays = windowDays
+	stats.WindowHours = hours
+	return stats, nil
+}
+
+func (s *Store) sendStats(column, ref string, since time.Time, hours float64) (SendStats, error) {
+	sinceStr := since.UTC().Format(time.RFC3339)
+
+	var total int64
+	err := s.db.QueryRow(
+		`SELECT COUNT(DISTINCT queue_id) FROM send_log
+		 WHERE `+column+` = ? AND status != ? AND created_at >= ?`,
+		ref, StatusRejected, sinceStr,
+	).Scan(&total)
+	if err != nil {
+		return SendStats{}, fmt.Errorf("send stats total %s %q: %w", column, ref, err)
+	}
+
+	var peak int64
+	err = s.db.QueryRow(
+		`SELECT COALESCE(MAX(bucket_count), 0) FROM (
+		   SELECT COUNT(DISTINCT queue_id) AS bucket_count FROM send_log
+		   WHERE `+column+` = ? AND status != ? AND created_at >= ?
+		   GROUP BY substr(created_at, 1, 13)
+		 )`,
+		ref, StatusRejected, sinceStr,
+	).Scan(&peak)
+	if err != nil {
+		return SendStats{}, fmt.Errorf("send stats peak %s %q: %w", column, ref, err)
+	}
+
+	avg := float64(total) / hours
+	return SendStats{Total: total, PeakPerHour: peak, AvgPerHour: avg}, nil
+}