Make tests that wait for concurrent work wait on the event or a condition with a long deadline (issue 1814)

A test that slept a fixed time and then asserted what a goroutine, process or
watcher did failed under the checker's load. Each now waits for its positive
evidence (a started baseline, a call counted, a state reached) within 30 s, and
the concurrency-limit tests meet at a barrier instead of overlapping by sleep.

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

modules/brother/cmd/brother/feeder_test.go

@@ -181,7 +181,7 @@ func standInCapture(release <-chan struct{}, fail error) func(ctx context.Contex
 // waitFor polls until the condition holds.
 func waitFor(t *testing.T, what string, cond func() bool) {
 	t.Helper()
-	for i := 0; i < 400; i++ {
+	for i := 0; i < 3000; i++ {
 		if cond() {
 			return
 		}

modules/brother/cmd/brother/glass_test.go

@@ -181,7 +181,7 @@ func TestAFinishedGlassDocumentIsNotFiledAgainByItsExpiry(t *testing.T) {
 	if _, err := r.call(t, "scanner.scan", docArgs(id, true)); err != nil {
 		t.Fatal(err)
 	}
-	time.Sleep(400 * time.Millisecond)
+	waitFor(t, "the expired document to be closed and filed", func() bool { e, _ := os.ReadDir(folder); return len(e) >= 1 })
 	if e, _ := os.ReadDir(folder); len(e) != 1 {
 		t.Errorf("%d files, want 1", len(e))
 	}

modules/brother/cmd/brother/printlink_test.go

@@ -311,8 +311,13 @@ func TestASlowUploadAndPrintAnswersStartedNeverATimeout(t *testing.T) {
 	}
 	got, _ = r.call(t, "printer.print", map[string]any{"path": "/home/ops/.ssh/id_ed25519", "node": "g14"})
 	id2, _ := got.(map[string]any)["ask"].(string)
-	time.Sleep(300 * time.Millisecond)
-	if _, err := r.call(t, "printer.print", map[string]any{"ask": id2}); err == nil || !strings.Contains(err.Error(), "refused by name") {
-		t.Errorf("the failed upload's outcome: %v", err)
+	var outcome error
+	for end := time.Now().Add(30 * time.Second); time.Now().Before(end); time.Sleep(10 * time.Millisecond) {
+		if _, outcome = r.call(t, "printer.print", map[string]any{"ask": id2}); outcome != nil {
+			break
+		}
+	}
+	if outcome == nil || !strings.Contains(outcome.Error(), "refused by name") {
+		t.Errorf("the failed upload's outcome: %v", outcome)
 	}
 }