diff --git a/modules/mesh-build-go/cmd/mesh-build-go/levels.go b/modules/mesh-build-go/cmd/mesh-build-go/levels.go
index d247f1a9..05f20600 100644
--- a/modules/mesh-build-go/cmd/mesh-build-go/levels.go
+++ b/modules/mesh-build-go/cmd/mesh-build-go/levels.go
@@ -73,7 +73,7 @@ type TestResult struct {
 	Elapsed float64 `json:"elapsed"`
 	// Setup is the level's setup time in seconds, when it has a setup.
 	Setup float64 `json:"setup,omitempty"`
-	// Lint is the unit level's gofmt and go vet time in seconds, before its tests (ADR 0529 §1).
+	// Lint is the unit level's gofmt and go vet time in seconds, run beside its tests (ADR 0529 §1; issue 1921).
 	Lint float64 `json:"lint,omitempty"`
 	// Bound and SetupBound are the bounds the level was judged by, in seconds.
 	Bound      float64    `json:"bound"`
diff --git a/modules/mesh-build-go/cmd/mesh-build-go/lint.go b/modules/mesh-build-go/cmd/mesh-build-go/lint.go
index 6accd280..75240ec5 100644
--- a/modules/mesh-build-go/cmd/mesh-build-go/lint.go
+++ b/modules/mesh-build-go/cmd/mesh-build-go/lint.go
@@ -188,14 +188,17 @@ func (m *Module) lint(ctx context.Context, run forgekey.Runner, tree, d string,
 
 // lintAll lints each directory, up to m.parallel() at once like the level's tests; the failures join in directory order
 // and the error is the first directory's, so the answer does not depend on which ended first (issue 1930). byDir names
-// the packages the level runs in each directory (packagesByDir); nil lints each directory whole.
-func (m *Module) lintAll(ctx context.Context, run forgekey.Runner, tree string, dirs []string, env func(d string) []string, byDir map[string][]string) ([]Failure, error) {
+// the packages the level runs in each directory (packagesByDir); nil lints each directory whole. slots is the bound the
+// lint shares with the level's tests; nil gives it one of its own.
+func (m *Module) lintAll(ctx context.Context, run forgekey.Runner, tree string, dirs []string, env func(d string) []string, byDir map[string][]string, slots chan struct{}) ([]Failure, error) {
 	type answer struct {
 		failed []Failure
 		err    error
 	}
 	answers := make([]answer, len(dirs))
-	slots := make(chan struct{}, m.parallel())
+	if slots == nil {
+		slots = make(chan struct{}, m.parallel())
+	}
 	var wg sync.WaitGroup
 	var crash any // a panic of a lint goes on in the caller, as a panic of a test run does
 	var crashMu sync.Mutex
diff --git a/modules/mesh-build-go/cmd/mesh-build-go/lint_test.go b/modules/mesh-build-go/cmd/mesh-build-go/lint_test.go
index ec4ac01a..3f0d3126 100644
--- a/modules/mesh-build-go/cmd/mesh-build-go/lint_test.go
+++ b/modules/mesh-build-go/cmd/mesh-build-go/lint_test.go
@@ -10,6 +10,7 @@ import (
 	"testing"
 	"time"
 
+	"git.novox.be/novox/mesh-sdk/go/delivery"
 	"git.novox.be/novox/mesh-sdk/go/forgekey"
 )
 
@@ -76,7 +77,7 @@ func TestTheUnitLevelRunsGofmtAndVetWithEveryTag(t *testing.T) {
 
 // 1887/D7-go: through the step, the unit level of a tree holding an unformatted file fails, naming the file.
 func TestAnUnformattedFileFailsTheUnitLevel(t *testing.T) {
-	m, states, ws, calls := workspaceFor(t, "empty")
+	m, states, ws, _ := workspaceFor(t, "empty")
 	tree := filepath.Join(m.Work, ws, "tree")
 	for name, body := range map[string]string{"go.mod": "module x\n", "x.go": "package x\nfunc X()   {}\n"} {
 		if err := os.WriteFile(filepath.Join(tree, name), []byte(body), 0o644); err != nil {
@@ -87,51 +88,49 @@ func TestAnUnformattedFileFailsTheUnitLevel(t *testing.T) {
 	if res.Passed || len(res.Failed) != 1 || res.Failed[0].Test != "gofmt" || !strings.Contains(res.Failed[0].Output, "x.go") {
 		t.Fatalf("result = %+v, want the level failed naming x.go", res)
 	}
-	// Review round 2 item 5: before the level's tests, which do not run once gofmt failed.
-	for _, c := range *calls {
-		if strings.Contains(c.line, " test -json") {
-			t.Errorf("the tests ran after gofmt failed: %s", c.line)
-		}
-	}
 }
 
-// Issue 1930: the lint of many directories runs side by side up to the level's bound, not one after another, and the
-// failures still join in directory order.
-func TestTheLintOfManyDirectoriesRunsAtOnceUpToTheBound(t *testing.T) {
-	files := map[string]string{}
-	var dirs []string
-	for _, d := range []string{"a", "b", "c", "d", "e", "f"} {
-		files[d+"/go.mod"] = "module x/" + d + "\n"
-		files[d+"/x.go"] = "package x\n"
-		dirs = append(dirs, d)
-	}
-	tree := writeTree(t, files)
-	var mu sync.Mutex
-	running, most := 0, 0
-	run := func(ctx context.Context, env []string, name string, args ...string) forgekey.Ran {
-		mu.Lock()
-		running++
-		most = max(most, running)
-		mu.Unlock()
-		time.Sleep(30 * time.Millisecond)
-		mu.Lock()
-		running--
-		mu.Unlock()
-		if strings.HasSuffix(args[1], "b") || strings.HasSuffix(args[1], "e") {
-			return forgekey.Ran{Status: 1, Stderr: "bad " + filepath.Base(args[1])}
+// 1921/S4: the lint runs beside the unit level's tests, not before them: both have started before either ends, a lint
+// failure still fails the level, and the result reports the lint's time and the tests' failures both.
+func TestTheLintRunsBesideTheUnitTestsAndItsFailureStillFailsTheLevel(t *testing.T) {
+	m, states, ws, _ := workspaceFor(t, "failing")
+	tree := filepath.Join(m.Work, ws, "tree")
+	for name, body := range map[string]string{"go.mod": "module fixture/failing\n", "x.go": "package x\nfunc X()   {}\n"} {
+		if err := os.WriteFile(filepath.Join(tree, name), []byte(body), 0o644); err != nil {
+			t.Fatal(err)
 		}
-		return forgekey.Ran{}
 	}
-	m := &Module{Parallel: 3}
-	failed, err := m.lintAll(context.Background(), run, tree, dirs, func(string) []string { return nil }, nil)
-	if err != nil {
-		t.Fatal(err)
+	m.Parallel = 4
+	inner := m.Run
+	var vetStarted, testStarted sync.Once
+	vet, test := make(chan struct{}), make(chan struct{})
+	timeout := time.After(2 * time.Second)
+	m.Run = func(ctx context.Context, env []string, name string, args ...string) forgekey.Ran {
+		line := strings.Join(args, " ")
+		switch {
+		case strings.Contains(line, " vet "):
+			vetStarted.Do(func() { close(vet) })
+			select { // the vet ends only once a test has started
+			case <-test:
+			case <-timeout:
+				t.Error("no test started while the vet ran")
+			}
+		case strings.Contains(line, " test -json"):
+			testStarted.Do(func() { close(test) })
+			select {
+			case <-vet:
+			case <-timeout:
+				t.Error("no vet started while the tests ran")
+			}
+		}
+		return inner(ctx, env, name, args...)
 	}
-	if most < 2 || most > 3 {
-		t.Errorf("%d lint commands ran at once, want 2 or 3 (the bound)", most)
+	res, st := runUnit(t, m, states, ws)
+	if st.State != delivery.StepPassed {
+		t.Fatalf("the step ended %s: %s", st.State, st.Reason)
 	}
-	if len(failed) != 2 || failed[0].Package != "b" || failed[1].Package != "e" {
-		t.Errorf("failed = %+v, want b's then e's", failed)
+	if res.Passed || len(res.Failed) < 2 || res.Failed[0].Test != "gofmt" || res.Failed[1].Test != "TestThreeIsFour" {
+		t.Fatalf("failed = %+v, want gofmt's failure, then the test's", res.Failed)
 	}
 }
 
diff --git a/modules/mesh-build-go/cmd/mesh-build-go/test.go b/modules/mesh-build-go/cmd/mesh-build-go/test.go
index 97a86bbc..931192d2 100644
--- a/modules/mesh-build-go/cmd/mesh-build-go/test.go
+++ b/modules/mesh-build-go/cmd/mesh-build-go/test.go
@@ -205,29 +205,35 @@ func (m *Module) runLevel(ctx context.Context, tree string, o levelOpts) (*TestR
 			todo = append(todo, d)
 		}
 	}
+	// The level's commands share one bound on processes: the lint's and the tests' (issue 1921, try speed S4).
+	slots := make(chan struct{}, m.parallel())
+	var lintFailed []Failure
+	var lintErr error
+	var lintDone chan struct{}
+	var crash any // a panic of a run or of the lint goes on in the caller, which cleans up after it
+	var crashMu sync.Mutex
 	if o.level == LevelUnit {
-		// gofmt and go vet of each directory the level runs come before its tests (ADR 0529 §1; issue 1887 D7-go): a
-		// directory that fails them fails the level at once, and their time is the result's Lint.
-		linted := m.clock()
-		failed, err := m.lintAll(ctx, run, tree, todo, func(d string) []string {
-			return append(m.goEnvFor(filepath.Join(tree, d)), o.env...)
-		}, byDir)
-		if err != nil {
-			return nil, err
-		}
-		res.Lint = m.clock().Sub(linted).Seconds()
-		if len(failed) > 0 {
-			res.Failed = failed
-			res.judge(o.bounds)
-			return res, nil
-		}
-		began = m.clock() // the level's running time is its tests'
+		// gofmt and go vet of each directory the level runs, beside its tests (ADR 0529 §1; issue 1887 D7-go; issue 1921,
+		// try speed S4): a directory that fails them fails the level, and their time is the result's Lint.
+		lintDone = make(chan struct{})
+		go func() {
+			defer close(lintDone)
+			defer func() {
+				if p := recover(); p != nil {
+					crashMu.Lock()
+					crash = p
+					crashMu.Unlock()
+				}
+			}()
+			linted := m.clock()
+			lintFailed, lintErr = m.lintAll(ctx, run, tree, todo, func(d string) []string {
+				return append(m.goEnvFor(filepath.Join(tree, d)), o.env...)
+			}, byDir, slots)
+			res.Lint = m.clock().Sub(linted).Seconds()
+		}()
 	}
 	runs := make([]dirRun, len(todo))
-	slots := make(chan struct{}, m.parallel())
 	var wg sync.WaitGroup
-	var crash any // a panic of a run goes on in the caller, which cleans up after it
-	var crashMu sync.Mutex
 	for i, d := range todo {
 		wg.Add(1)
 		slots <- struct{}{}
@@ -258,9 +264,16 @@ func (m *Module) runLevel(ctx context.Context, tree string, o levelOpts) (*TestR
 		}()
 	}
 	wg.Wait()
+	if lintDone != nil {
+		<-lintDone
+	}
 	if crash != nil {
 		panic(crash)
 	}
+	if lintErr != nil {
+		return nil, lintErr
+	}
+	res.Failed = append(res.Failed, lintFailed...) // the lint's failures first, then the tests'
 	for i, d := range todo {
 		dr := runs[i]
 		if (dr.r.Status != 0 || dr.r.Err != "") && len(dr.rd.pkgs) == 0 {
diff --git a/modules/mesh-build-go/cmd/mesh-build-go/test_test.go b/modules/mesh-build-go/cmd/mesh-build-go/test_test.go
index aa6d1d1a..d55f9609 100644
--- a/modules/mesh-build-go/cmd/mesh-build-go/test_test.go
+++ b/modules/mesh-build-go/cmd/mesh-build-go/test_test.go
@@ -6,6 +6,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -25,8 +26,11 @@ func capturedRunner(t *testing.T, captured string, calls *[]cmdRecord) forgekey.
 	if strings.Contains(string(raw), `"Action":"fail"`) {
 		status = 1 // go test exits 1 when a test or a build failed
 	}
+	var mu sync.Mutex // the lint and the tests of a level run at once (issue 1921, try speed S4)
 	return func(ctx context.Context, env []string, name string, args ...string) forgekey.Ran {
+		mu.Lock()
 		*calls = append(*calls, cmdRecord{env: env, line: name + " " + strings.Join(args, " ")})
+		mu.Unlock()
 		switch {
 		case name == "git" && args[2] == "ls-files":
 			return forgekey.Ran{Stdout: "go.mod\n"}