Restructure stats into delta, mask, and aggregate layers

main.go

@@ -152,9 +152,11 @@ const (
 )
 
 // One sampler for both directions, so they are read back to back on one clock
-// rather than drifting apart on two.
+// rather than drifting apart on two. Whatever each tick lets through the mask
+// goes on into the history's buckets.
 type sampler struct {
 	dirs []*direction
+	hist *history
 }
 
 func (s *sampler) run(done *atomic.Bool, startTx <-chan struct{}) {
@@ -166,7 +168,7 @@ func (s *sampler) run(done *atomic.Bool, startTx <-chan struct{}) {
 	for !done.Load() {
 		<-tick.C
 		for _, d := range s.dirs {
-			d.sample()
+			s.hist.addFaults(time.Now(), d.sample())
 		}
 	}
 }
@@ -241,7 +243,7 @@ func run(aName, bName string) (err error) {
 
 	var dirs []*direction
 	for _, p := range [][2]endpoint{{a, b}, {b, a}} {
-		d, err := buildDirection(p[0].name+"->"+p[1].name, p[0], p[1], &diag.measuring)
+		d, err := buildDirection(p[0].name+"->"+p[1].name, p[0], p[1], &diag.masked)
 		if err != nil {
 			return err
 		}
@@ -277,7 +279,8 @@ func run(aName, bName string) (err error) {
 	for _, d := range dirs {
 		d.start(&wg, &done, &rxReady, startTx)
 	}
-	samp := &sampler{dirs: dirs}
+	hist := newHistory(time.Now())
+	samp := &sampler{dirs: dirs, hist: hist}
 	wg.Add(1)
 	go func() {
 		defer wg.Done()
@@ -289,7 +292,7 @@ func run(aName, bName string) (err error) {
 		go func() {
 			defer wg.Done()
 			defer holdPanic()
-			m.run(&done)
+			m.run(&done, hist)
 		}()
 	}
 	// Every return from here on stops the workers before the deferred closes
@@ -340,10 +343,9 @@ func run(aName, bName string) (err error) {
 	}
 
 	start := time.Now()
-	hist := newHistory(start)
 	// A reset resets at the press, then re-measures; the measure's failures
-	// are suppressed at their sources while it runs, so there is nothing to
-	// hide or revert afterwards.
+	// are dropped at the mask gate while it runs, so there is nothing to hide
+	// or revert afterwards.
 	kickMeasure := func() {
 		if diag.kick(&done) {
 			diag.resetLengths()