Hold the keys in the walk-beside test so its walks stay open (issue 1931)

cmd/mesh-controller/beside_test.go

@@ -4,6 +4,7 @@ package main
 
 import (
 	"strings"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -15,6 +16,14 @@ import (
 func TestAnUnrelatedBatchWalksBesideAnOpenWalk(t *testing.T) {
 	open := windowed(t)
 	asksWithPaths(t)
+	// Both modules' keys are not built, so each walk stays open as it did while its build ran: with the stand-in
+	// builder's key done at once, one step would carry a one-module walk to done.
+	wholeKeys, held := openPlanKeys, &atomic.Bool{}
+	held.Store(true)
+	openPlanKeys = func() (planKeyReads, func(), error) {
+		all, done, err := wholeKeys()
+		return keysHolding{keysHolding{all, "one", held, ""}, "two", held, ""}, done, err
+	}
 	ctx := t.Context()
 	hear(t, open, repoMerge("one", "c1", t0), t0)
 	cutAt(t, open, t0.Add(90*time.Second))