Show each entrypoint's last event and event count on the webhook page (closes #393)

Each entrypoint in the webhook page's entrypoint list now shows when its last event arrived (relative, with the full UTC time on hover), or "never", and how many events arrived through it within the webhook's retention period. Both come from one query per page, grouped by entrypoint, over a new events index on entrypoint_id, deleted_at and created_at, so the page reads only the index entries it counts. Pre-1.0: the index goes into the schema in place. A test checks the database's plan for the statement as the code builds it; another shows two entrypoints with different traffic each with their own figures, an event older than retention left out, and an unused entrypoint reading "never".

Model: opus-5-5

internal/database/event_tier_indexes_test.go

@@ -233,6 +233,42 @@ func TestResubmitCountUsesItsIndex(t *testing.T) {
 			"(resubmitted_from_id=? AND deleted_at=?)")
 }
 
+// TestEntrypointEventsUseTheirIndex does the same for the webhook
+// page's figures for each entrypoint, the events since the retention
+// cutoff and when the newest arrived (addEntrypointEvents in the
+// handlers), which must come from the index alone. It passes 25
+// entrypoints, as TestResubmitCountUsesItsIndex passes 25 events.
+func TestEntrypointEventsUseTheirIndex(t *testing.T) {
+	t.Parallel()
+
+	mgr, lc := setupTestWebhookDBManager(t)
+	ctx := context.Background()
+	require.NoError(t, lc.Start(ctx))
+
+	defer func() { require.NoError(t, lc.Stop(ctx)) }()
+
+	db, err := mgr.GetDB(uuid.New().String())
+	require.NoError(t, err)
+
+	dry := db.Session(&gorm.Session{DryRun: true})
+
+	entrypoints := make([]string, 25)
+	for i := range entrypoints {
+		entrypoints[i] = uuid.New().String()
+	}
+
+	var rows []struct{ Events int }
+
+	assertPlanUses(t, db, dry.Model(&database.Event{}).
+		Select("entrypoint_id, count(*) AS events, "+
+			"max(created_at), created_at AS last_event_at").
+		Where("entrypoint_id IN ?", entrypoints).
+		Where("created_at >= ?", time.Now()).
+		Group("entrypoint_id").Find(&rows),
+		"COVERING INDEX idx_events_entrypoint_id "+
+			"(entrypoint_id=? AND deleted_at=? AND created_at>?)")
+}
+
 // assertPlanUses asserts that SQLite's plan for a statement GORM built
 // in a dry run, run with the same SQL and arguments GORM would send,
 // names each of the given indexes.