checker: keep 1 report per hour after the first day

Insert an hourly tier between the full-detail window and the daily
bucket so users still get sub-day resolution for the first week:

  0..1 day  -> all
  1..7 days -> 1 per hour
  7..30     -> 2 per day
  ...

internal/usecase/checker/retention.go

@@ -37,7 +37,8 @@ import (
 //
 //	  age window                | kept
 //	  ------------------------- | ------------------------------------------
-//	  0 .. 7 days               | every execution
+//	  0 .. 1 day                | every execution
+//	  1 .. 7 days               | up to 1 execution per hour per (checker,target)
 //	  7 .. 30 days              | up to 2 executions per day per (checker,target)
 //	  30 .. D/2 days            | up to 1 execution per week per (checker,target)
 //	  D/2 .. D days             | up to 1 execution per month per (checker,target)
@@ -52,7 +53,11 @@ type RetentionPolicy struct {
 
 	// FullDetailDays: every execution kept under this age.
 	FullDetailDays int
-	// DailyBucketDays: between FullDetailDays and DailyBucketDays, keep
+	// HourlyBucketDays: between FullDetailDays and HourlyBucketDays, keep
+	// PerHourKept executions per UTC hour per (checker,target).
+	HourlyBucketDays int
+	PerHourKept      int
+	// DailyBucketDays: between HourlyBucketDays and DailyBucketDays, keep
 	// PerDayKept executions per UTC day per (checker,target).
 	DailyBucketDays int
 	PerDayKept      int
@@ -73,7 +78,9 @@ func DefaultRetentionPolicy(retentionDays int) RetentionPolicy {
 	}
 	return RetentionPolicy{
 		RetentionDays:    retentionDays,
-		FullDetailDays:   7,
+		FullDetailDays:   1,
+		HourlyBucketDays: 7,
+		PerHourKept:      1,
 		DailyBucketDays:  30,
 		PerDayKept:       2,
 		WeeklyBucketDays: max(retentionDays/2, 31),
@@ -104,6 +111,7 @@ func (p RetentionPolicy) Decide(executions []*happydns.Execution, now time.Time)
 
 	hardCutoff := now.AddDate(0, 0, -p.RetentionDays)
 	fullCutoff := now.AddDate(0, 0, -p.FullDetailDays)
+	hourlyCutoff := now.AddDate(0, 0, -p.HourlyBucketDays)
 	dailyCutoff := now.AddDate(0, 0, -p.DailyBucketDays)
 	weeklyCutoff := now.AddDate(0, 0, -p.WeeklyBucketDays)
 
@@ -113,6 +121,7 @@ func (p RetentionPolicy) Decide(executions []*happydns.Execution, now time.Time)
 			return group[i].StartedAt.After(group[j].StartedAt)
 		})
 
+		hourBuckets := map[string]int{}
 		dayBuckets := map[string]int{}
 		weekBuckets := map[string]int{}
 		monthBuckets := map[string]int{}
@@ -125,6 +134,14 @@ func (p RetentionPolicy) Decide(executions []*happydns.Execution, now time.Time)
 			case !t.Before(fullCutoff):
 				// 0 .. FullDetailDays — keep everything.
 				keep = append(keep, e.Id)
+			case !t.Before(hourlyCutoff):
+				k := t.UTC().Format("2006-01-02T15")
+				if hourBuckets[k] < p.PerHourKept {
+					hourBuckets[k]++
+					keep = append(keep, e.Id)
+				} else {
+					drop = append(drop, e.Id)
+				}
 			case !t.Before(dailyCutoff):
 				k := t.UTC().Format("2006-01-02")
 				if dayBuckets[k] < p.PerDayKept {

internal/usecase/checker/retention_test.go

@@ -50,17 +50,38 @@ func TestDecide_FullDetailWindow(t *testing.T) {
 	now := time.Date(2026, 4, 8, 12, 0, 0, 0, time.UTC)
 	p := DefaultRetentionPolicy(365)
 
+	// 20 executions in the first 20 minutes — all inside 0..1 day window.
 	var execs []*happydns.Execution
-	for i := 0; i < 50; i++ {
-		execs = append(execs, mkExec(fmt.Sprintf("e%d", i), time.Duration(i)*time.Hour, now))
+	for i := 0; i < 20; i++ {
+		execs = append(execs, mkExec(fmt.Sprintf("e%d", i), time.Duration(i)*time.Minute, now))
 	}
 
 	keep, drop := p.Decide(execs, now)
 	if len(drop) != 0 {
-		t.Fatalf("expected no drops in <7d window, got %d", len(drop))
+		t.Fatalf("expected no drops in <1d window, got %d", len(drop))
 	}
-	if len(keep) != 50 {
-		t.Fatalf("expected 50 keeps, got %d", len(keep))
+	if len(keep) != 20 {
+		t.Fatalf("expected 20 keeps, got %d", len(keep))
+	}
+}
+
+func TestDecide_HourlyBucket(t *testing.T) {
+	now := time.Date(2026, 4, 8, 12, 0, 0, 0, time.UTC)
+	p := DefaultRetentionPolicy(365)
+
+	// 6 executions in the same hour ~3 days ago (inside hourly window).
+	var execs []*happydns.Execution
+	base := 3*24*time.Hour + 30*time.Minute
+	for i := 0; i < 6; i++ {
+		execs = append(execs, mkExec(fmt.Sprintf("e%d", i), base+time.Duration(i)*time.Minute, now))
+	}
+
+	keep, drop := p.Decide(execs, now)
+	if len(keep) != p.PerHourKept {
+		t.Fatalf("expected %d keeps in hourly bucket, got %d", p.PerHourKept, len(keep))
+	}
+	if len(drop) != 6-p.PerHourKept {
+		t.Fatalf("expected %d drops, got %d", 6-p.PerHourKept, len(drop))
 	}
 }