diff --git a/go/buildstep/askrun.go b/go/buildstep/askrun.go
index 9956271..7f0ee11 100644
--- a/go/buildstep/askrun.go
+++ b/go/buildstep/askrun.go
@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"path"
+	"slices"
 	"sort"
 	"strings"
 
@@ -162,19 +163,35 @@ func (s AskSteps) check(ctx context.Context, job delivery.CheckJob) (any, error)
 	if len(f.Conflicts) > 0 {
 		return answer, nil // the asker reads the conflict from the fetch's answer: a verdict, not an error
 	}
+	if s.Test == nil {
+		return nil, Refuse("this build module tests nothing")
+	}
 	runner := ""
 	if job.Runner != "" && (job.RunnerWhen == "" || changesUnder(f.Changed, job.RunnerWhen)) {
 		runner = job.Runner
 	}
+	for _, level := range job.Levels {
+		la := delivery.LevelAnswer{Level: level}
+		passed, err := s.level(ctx, job, level, f, runner, &la)
+		answer.Levels = append(answer.Levels, la)
+		if err != nil {
+			return nil, err
+		}
+		if !passed {
+			return answer, nil // the first level that did not pass ends the check (ADR 0484 clause 13)
+		}
+	}
+	return answer, nil
+}
+
+// level runs one level of a check ask and says whether it passed.
+func (s AskSteps) level(ctx context.Context, job delivery.CheckJob, level string, f fetched, runner string, la *delivery.LevelAnswer) (bool, error) {
 	withRunner := func(args map[string]any) map[string]any {
 		if runner != "" {
 			args["runner"] = runner
 		}
 		return args
 	}
-	if s.Test == nil {
-		return nil, Refuse("this build module tests nothing")
-	}
 	test := func(args map[string]any) (bool, error) {
 		out, err := s.Test(ctx, args)
 		if err != nil {
@@ -184,7 +201,7 @@ func (s AskSteps) check(ctx context.Context, job delivery.CheckJob) (any, error)
 		if err != nil {
 			return false, err
 		}
-		answer.Tests = append(answer.Tests, r)
+		la.Tests = append(la.Tests, r)
 		var t struct {
 			Passed bool `json:"passed"`
 		}
@@ -198,23 +215,20 @@ func (s AskSteps) check(ctx context.Context, job delivery.CheckJob) (any, error)
 				if changesTestIn(f.Changed, dir) != priority {
 					continue
 				}
-				passed, err := test(withRunner(map[string]any{"workspace": f.Workspace, "module": dir, "level": job.Level}))
+				passed, err := test(withRunner(map[string]any{"workspace": f.Workspace, "module": dir, "level": level}))
 				if err != nil {
-					return nil, fmt.Errorf("the %s level of %s: %w", job.Level, dir, err)
+					return false, fmt.Errorf("the %s level of %s: %w", level, dir, err)
 				}
 				if !passed {
-					return answer, nil
+					return false, nil
 				}
 			}
 		}
-		return answer, nil
-	}
-	todo, all, err := s.plan(ctx, job, f, withRunner, &answer)
-	if err != nil {
-		return nil, err
+		return true, nil
 	}
+	todo, all := s.plan(ctx, job, level, f, runner, withRunner, la)
 	for _, priority := range []bool{true, false} {
-		args := withRunner(map[string]any{"workspace": f.Workspace, "level": job.Level})
+		args := withRunner(map[string]any{"workspace": f.Workspace, "level": level})
 		if job.Run != "" {
 			args["run"] = job.Run
 		}
@@ -236,13 +250,13 @@ func (s AskSteps) check(ctx context.Context, job delivery.CheckJob) (any, error)
 		}
 		passed, err := test(args)
 		if err != nil {
-			return nil, fmt.Errorf("the %s level: %w", job.Level, err)
+			return false, fmt.Errorf("the %s level: %w", level, err)
 		}
 		if !passed {
-			return answer, nil
+			return false, nil
 		}
 	}
-	return answer, nil
+	return true, nil
 }
 
 // release removes an ask's workspace, saying a failure: the module's sweep removes it later.
@@ -255,30 +269,36 @@ func (s AskSteps) release(workspace string) {
 	}
 }
 
-// plan digests the level and takes the kept verdicts: the packages left to test, or all when the level runs whole (a
-// try of some tests, or a digest that named nothing).
-func (s AskSteps) plan(ctx context.Context, job delivery.CheckJob, f fetched, withRunner func(map[string]any) map[string]any, answer *delivery.CheckAnswer) ([]string, bool, error) {
-	if job.Run != "" {
-		return nil, true, nil // a partial run proves no package: nothing is taken or kept
+// plan digests the level and takes the kept verdicts: the packages left to test, or all when the level runs whole. It
+// runs whole, digesting nothing, for a try of some tests (a partial run proves no package) and under the candidate's own
+// runner (ADR 0535 §4: the candidate decides which verdicts would be taken, so every package runs); it runs whole and
+// takes nothing when the digest names no package or does not cover the siblings the fetch placed (ADR 0444, L5).
+func (s AskSteps) plan(ctx context.Context, job delivery.CheckJob, level string, f fetched, runner string, withRunner func(map[string]any) map[string]any, la *delivery.LevelAnswer) ([]string, bool) {
+	if job.Run != "" || runner != "" {
+		return nil, true
 	}
-	out, err := s.Digest(ctx, withRunner(map[string]any{"workspace": f.Workspace, "level": job.Level}))
+	out, err := s.Digest(ctx, withRunner(map[string]any{"workspace": f.Workspace, "level": level}))
 	if err != nil {
 		if s.Logf != nil {
-			s.Logf("no digest of the %s level, so it runs whole: %v", job.Level, err)
+			s.Logf("no digest of the %s level, so it runs whole: %v", level, err)
 		}
-		return nil, true, nil
+		return nil, true
 	}
 	r, err := raw(out)
 	if err != nil {
-		return nil, true, nil
+		return nil, true
 	}
-	answer.Digest = r
 	var d struct {
 		Packages map[string]string `json:"packages"`
+		Beside   []string          `json:"beside"`
 	}
 	if err := json.Unmarshal(r, &d); err != nil || len(d.Packages) == 0 {
-		return nil, true, nil
+		return nil, true
 	}
+	if !slices.Equal(d.Beside, besideOf(job.Fetch)) {
+		return nil, true // a digest that does not cover the siblings keys no verdict: the level runs whole, keeping nothing
+	}
+	la.Digest = r
 	pkgs := make([]string, 0, len(d.Packages))
 	for p := range d.Packages {
 		pkgs = append(pkgs, p)
@@ -287,21 +307,37 @@ func (s AskSteps) plan(ctx context.Context, job delivery.CheckJob, f fetched, wi
 	var todo []string
 	for _, p := range pkgs {
 		if job.Kept && s.Kept != nil {
-			tests, found, err := s.Kept(ctx, job.Level, d.Packages[p])
+			tests, found, err := s.Kept(ctx, level, d.Packages[p])
 			if err != nil && s.Logf != nil {
-				s.Logf("the kept verdict of %s at %s cannot be read, so it runs: %v", p, job.Level, err)
+				s.Logf("the kept verdict of %s at %s cannot be read, so it runs: %v", p, level, err)
 			}
 			if err == nil && found {
-				answer.Kept = append(answer.Kept, delivery.KeptTaken{Package: p, Digest: d.Packages[p], Tests: tests})
+				la.Kept = append(la.Kept, delivery.KeptTaken{Package: p, Digest: d.Packages[p], Tests: tests})
 				continue
 			}
 		}
 		todo = append(todo, p)
 	}
-	if len(todo) == 0 {
-		return nil, false, nil
+	return todo, false
+}
+
+// besideOf are the siblings a fetch's arguments place, as a digest echoes them: `<owner/repo> <commit>`, sorted.
+func besideOf(fetch map[string]any) []string {
+	raw, err := json.Marshal(fetch["beside"])
+	if err != nil {
+		return nil
 	}
-	return todo, false, nil
+	var refs []struct {
+		Repository string `json:"repository"`
+		Commit     string `json:"commit"`
+	}
+	_ = json.Unmarshal(raw, &refs)
+	var out []string
+	for _, r := range refs {
+		out = append(out, r.Repository+" "+r.Commit)
+	}
+	sort.Strings(out)
+	return out
 }
 
 // changesUnder says whether a path the merge changes is under prefix.
diff --git a/go/buildstep/askrun_test.go b/go/buildstep/askrun_test.go
index 34c5e26..473c2a1 100644
--- a/go/buildstep/askrun_test.go
+++ b/go/buildstep/askrun_test.go
@@ -109,28 +109,57 @@ func TestRunAskRefusesAnotherToolchain(t *testing.T) {
 	}
 }
 
-// 1887/A3, issue 1887 design limit 1: a check ask digests the level, takes the kept verdicts, tests the packages whose
-// tests changed first, and stops at the first failure.
-func TestRunAskChecksAGoLevel(t *testing.T) {
+// 1887/A3, A5a, issue 1887 design limit 1: a check ask runs the levels of one check after one fetch: it digests the unit
+// level, takes the kept verdicts, tests the packages whose tests changed first, and stops at the first failure, running
+// no later level.
+func TestRunAskChecksTheLevelsOfOneCheck(t *testing.T) {
 	r := &recorder{
 		fetch:   map[string]any{"workspace": "/w", "changed": []string{"pkg/b/b_test.go"}},
 		digests: map[string]string{"x/pkg/a": "d-a", "x/pkg/b": "d-b", "x/pkg/k": "d-kept"},
 		tests:   map[string]bool{"x/pkg/a": true, "x/pkg/b": false},
 	}
-	out, err := RunAsk(context.Background(), r.steps(), ask(delivery.CheckJob{Level: delivery.LevelUnit, Kept: true,
-		Runner: "workspace", RunnerWhen: "pkg/b/", Fetch: map[string]any{"repository": "novox/x", "commit": runCommit, "base": runCommit}}))
+	out, err := RunAsk(context.Background(), r.steps(), ask(delivery.CheckJob{Levels: []string{delivery.LevelUnit, delivery.LevelIntegration}, Kept: true,
+		Runner: "workspace", RunnerWhen: "modules/mesh-build-go/", Fetch: map[string]any{"repository": "novox/x", "commit": runCommit, "base": runCommit}}))
 	if err != nil {
 		t.Fatal(err)
 	}
-	got := strings.Join(r.calls[1:], "\n")
-	want := `digest {"level":"unit","runner":"workspace","workspace":"/w"}
-test {"level":"unit","packages":["x/pkg/b"],"runner":"workspace","workspace":"/w"}`
+	got := strings.Join(r.calls, "\n")
+	want := `fetch {"base":"` + runCommit + `","commit":"` + runCommit + `","repository":"novox/x"}
+digest {"level":"unit","workspace":"/w"}
+test {"level":"unit","packages":["x/pkg/b"],"workspace":"/w"}`
 	if got != want {
 		t.Fatalf("calls:\n%s\nwant:\n%s", got, want)
 	}
 	a := out.(delivery.CheckAnswer)
-	if len(a.Kept) != 1 || a.Kept[0].Package != "x/pkg/k" || a.Kept[0].Tests != 7 || len(a.Tests) != 1 || len(a.Digest) == 0 {
-		t.Fatalf("answer %+v", a)
+	if len(a.Levels) != 1 {
+		t.Fatalf("levels %+v, want the unit level alone", a.Levels)
+	}
+	u := a.Levels[0]
+	if u.Level != delivery.LevelUnit || len(u.Kept) != 1 || u.Kept[0].Package != "x/pkg/k" || u.Kept[0].Tests != 7 || len(u.Tests) != 1 || len(u.Digest) == 0 {
+		t.Fatalf("the unit level %+v", u)
+	}
+}
+
+// ADR 0535 §4: a merge that changes the build module's own code is judged by the candidate's runner, every package run
+// and nothing digested or kept; a digest that does not cover the fetch's siblings runs the level whole too.
+func TestRunAskRunsWholeUnderTheRunnerOrWithoutTheSiblings(t *testing.T) {
+	r := &recorder{fetch: map[string]any{"workspace": "/w", "changed": []string{"modules/mesh-build-go/x.go"}},
+		digests: map[string]string{"x/pkg/a": "d-kept"}, tests: map[string]bool{}}
+	if _, err := RunAsk(context.Background(), r.steps(), ask(delivery.CheckJob{Levels: []string{delivery.LevelUnit}, Kept: true,
+		Runner: "workspace", RunnerWhen: "modules/mesh-build-go/", Fetch: map[string]any{"repository": "novox/x", "commit": runCommit}})); err != nil {
+		t.Fatal(err)
+	}
+	if got := strings.Join(r.calls[1:], "\n"); got != `test {"level":"unit","runner":"workspace","workspace":"/w"}` {
+		t.Fatalf("under the runner: %s", got)
+	}
+	r = &recorder{fetch: map[string]any{"workspace": "/w"}, digests: map[string]string{"x/pkg/a": "d-kept"}, tests: map[string]bool{}}
+	out, err := RunAsk(context.Background(), r.steps(), ask(delivery.CheckJob{Levels: []string{delivery.LevelUnit}, Kept: true,
+		Fetch: map[string]any{"repository": "novox/x", "commit": runCommit, "beside": []any{map[string]any{"repository": "novox/mesh-sdk", "commit": runCommit}}}}))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if l := out.(delivery.CheckAnswer).Levels[0]; len(l.Kept) != 0 || len(l.Digest) != 0 {
+		t.Fatalf("a digest without the siblings kept %+v", l)
 	}
 }
 
@@ -141,15 +170,15 @@ func TestRunAskChecksNodeModulesAndConflicts(t *testing.T) {
 		tests: map[string]bool{"a": true, "b": true}}
 	s := r.steps()
 	s.Digest = nil
-	if _, err := RunAsk(context.Background(), s, ask(delivery.CheckJob{Level: delivery.LevelUnit, Fetch: map[string]any{"repository": "novox/x", "commit": runCommit}})); err != nil {
+	if _, err := RunAsk(context.Background(), s, ask(delivery.CheckJob{Levels: []string{delivery.LevelUnit}, Fetch: map[string]any{"repository": "novox/x", "commit": runCommit}})); err != nil {
 		t.Fatal(err)
 	}
 	if fmt.Sprint(r.calls[1:]) != `[test {"level":"unit","module":"b","workspace":"/w"} test {"level":"unit","module":"a","workspace":"/w"}]` {
 		t.Fatalf("calls %v", r.calls)
 	}
 	r = &recorder{fetch: map[string]any{"workspace": "/w", "conflicts": []string{"go.mod"}}}
-	out, err := RunAsk(context.Background(), r.steps(), ask(delivery.CheckJob{Level: delivery.LevelUnit, Fetch: map[string]any{"repository": "novox/x", "commit": runCommit}}))
-	if err != nil || len(r.calls) != 1 || len(out.(delivery.CheckAnswer).Tests) != 0 {
+	out, err := RunAsk(context.Background(), r.steps(), ask(delivery.CheckJob{Levels: []string{delivery.LevelUnit}, Fetch: map[string]any{"repository": "novox/x", "commit": runCommit}}))
+	if err != nil || len(r.calls) != 1 || len(out.(delivery.CheckAnswer).Levels) != 0 {
 		t.Fatalf("a conflict: %v %v", err, r.calls)
 	}
 }
diff --git a/go/buildstep/pull_test.go b/go/buildstep/pull_test.go
index e0d7af6..10fdedb 100644
--- a/go/buildstep/pull_test.go
+++ b/go/buildstep/pull_test.go
@@ -46,7 +46,7 @@ func testAsk(kind string) delivery.StepAsk {
 		b.Fetch = fetch
 		a.Build = &b
 	} else {
-		a.Check = &delivery.CheckJob{Fetch: fetch, Level: delivery.LevelUnit}
+		a.Check = &delivery.CheckJob{Fetch: fetch, Levels: []string{delivery.LevelUnit}}
 	}
 	return a
 }
diff --git a/go/delivery/stepasks.go b/go/delivery/stepasks.go
index f7ef11f..5cda634 100644
--- a/go/delivery/stepasks.go
+++ b/go/delivery/stepasks.go
@@ -183,21 +183,24 @@ type AskArtifact struct {
 	From     string `json:"from,omitempty"`
 }
 
-// CheckJob is a check ask's job: fetch the head merged onto its trunk, digest the level's packages, take the kept
-// verdicts for the digests that have one, and test the rest at Level, the packages the change's own tests are in first
-// (CheckAnswer).
+// CheckJob is a check ask's job, the levels of one check (ADR 0525 §3): fetch the head merged onto its trunk once, then
+// for each level in order digest its packages, take the kept verdicts for the digests that have one, and test the rest,
+// the packages the change's own tests are in first, stopping at the first level that does not pass (CheckAnswer).
 type CheckJob struct {
 	// Fetch is the fetch tool's arguments (repository, commit, ref, base, and the build module's own: beside, package).
 	Fetch map[string]any `json:"fetch"`
-	Level string         `json:"level"`
+	// Levels are run in this order (LevelUnit, LevelIntegration); a try may name one.
+	Levels []string `json:"levels"`
 	// Kept says the build module takes the kept verdicts of the checker's kept bucket (CheckerKeptBucket, by KeptKey)
-	// for the packages whose digest has one, and tests only the others. A try that runs some tests (Run) keeps nothing.
+	// for the packages whose digest has one and covers the siblings the fetch placed, and tests only the others (issue
+	// 1887's design limit 1). A try that runs some tests (Run), and a level the candidate's own build module judges
+	// (Runner), keep nothing.
 	Kept bool `json:"kept,omitempty"`
 	// Runner is the test step's runner ("workspace": the candidate's own build module judges it, ADR 0535 §4), used
 	// when the merge changes a path under RunnerWhen (every merge when RunnerWhen is empty).
 	Runner     string `json:"runner,omitempty"`
 	RunnerWhen string `json:"runner_when,omitempty"`
-	// Run is a try's test pattern (go test -run): the level runs it alone, digesting nothing.
+	// Run is a try's test pattern (go test -run): each level runs it alone, digesting nothing.
 	Run string `json:"run,omitempty"`
 }
 
@@ -259,8 +262,13 @@ func (b BuildJob) check(id string) error {
 }
 
 func (c CheckJob) check(id string) error {
-	if err := checkLevel(c.Level); err != nil {
-		return err
+	if len(c.Levels) == 0 {
+		return fmt.Errorf("delivery: the check ask %s names no level", id)
+	}
+	for _, l := range c.Levels {
+		if err := checkLevel(l); err != nil {
+			return err
+		}
 	}
 	return checkFetchArgs(id, c.Fetch)
 }
@@ -327,11 +335,18 @@ type AskBuilt struct {
 	Reference string `json:"reference,omitempty"`
 }
 
-// CheckAnswer is a check ask's step result, each part the build module's own tool's answer whole: the fetch's, the
-// digest's (absent when nothing was digested), the kept verdicts taken, and one test result per test step run, in the
-// order run. The checker judges and keeps from it as it did from the tools' answers.
+// CheckAnswer is a check ask's step result, each part the build module's own tool's answer whole: the fetch's, then one
+// LevelAnswer per level run, in order; a level that did not pass is the last. The checker judges and keeps from it as it
+// did from the tools' answers.
 type CheckAnswer struct {
-	Fetch  json.RawMessage   `json:"fetch"`
+	Fetch  json.RawMessage `json:"fetch"`
+	Levels []LevelAnswer   `json:"levels,omitempty"`
+}
+
+// LevelAnswer is one level of a check ask: the digest's answer (absent when nothing was digested: the level ran whole and
+// keeps nothing), the kept verdicts taken, and one test result per test step run, in the order run.
+type LevelAnswer struct {
+	Level  string            `json:"level"`
 	Digest json.RawMessage   `json:"digest,omitempty"`
 	Kept   []KeptTaken       `json:"kept,omitempty"`
 	Tests  []json.RawMessage `json:"tests,omitempty"`
diff --git a/go/delivery/stepasks_test.go b/go/delivery/stepasks_test.go
index 1cf1ad6..9ac39a5 100644
--- a/go/delivery/stepasks_test.go
+++ b/go/delivery/stepasks_test.go
@@ -23,7 +23,7 @@ func checkAsk() StepAsk {
 	return StepAsk{ID: "mh3k2x9qa1b2c4", Kind: AskCheck, Language: AskNode, Asker: "mesh-delivery-checker",
 		At: time.Date(2026, 10, 23, 13, 0, 0, 0, time.UTC),
 		Check: &CheckJob{Fetch: map[string]any{"repository": "novox/mesh-catalog", "commit": askCommit, "ref": "refs/pull/3/head", "base": askCommit},
-			Level: LevelUnit, Kept: true, Runner: "workspace", RunnerWhen: "modules/mesh-build-go/", Run: ""}}
+			Levels: []string{LevelUnit, LevelIntegration}, Kept: true, Runner: "workspace", RunnerWhen: "modules/mesh-build-go/", Run: ""}}
 }
 
 // 1887/A1a: an ask encodes and decodes with every field.
@@ -51,7 +51,7 @@ func TestAskRefusesUnknownKindAndLanguage(t *testing.T) {
 		"language": func(a *StepAsk) { a.Language = "typescript" },
 		"id":       func(a *StepAsk) { a.ID = "postgres" },
 		"neither":  func(a *StepAsk) { a.Build = nil },
-		"both":     func(a *StepAsk) { a.Check = &CheckJob{Level: LevelUnit, Fetch: a.Build.Fetch} },
+		"both":     func(a *StepAsk) { a.Check = &CheckJob{Levels: []string{LevelUnit}, Fetch: a.Build.Fetch} },
 		"recheck":  func(a *StepAsk) { a.Kind = AskRecheck },
 		"commit":   func(a *StepAsk) { a.Build.Fetch = map[string]any{"repository": "novox/x", "commit": "main"} },
 		"path":     func(a *StepAsk) { a.Build.Path = "" },