contracts/go/seats/nodebuildgo/contract.go

@@ -485,7 +485,7 @@ type StepAskCompose struct {
 	Fetch   Fetch  `json:"fetch"`
 	Package string `json:"package"`
 	Reader  string `json:"reader,omitempty"`
-	// the compose-candidate request
+	// the compose-candidate request, in one of two forms: the request as a JSON object, or, for one near the bus's message limit, a JSON string "gzip+base64:" followed by the base64 of the request object gzip-compressed; a holder that does not know the packed form refuses it, naming that it holds no request object
 	Request any `json:"request"`
 }
 

contracts/go/seats/nodebuildimage/contract.go

@@ -485,7 +485,7 @@ type StepAskCompose struct {
 	Fetch   Fetch  `json:"fetch"`
 	Package string `json:"package"`
 	Reader  string `json:"reader,omitempty"`
-	// the compose-candidate request
+	// the compose-candidate request, in one of two forms: the request as a JSON object, or, for one near the bus's message limit, a JSON string "gzip+base64:" followed by the base64 of the request object gzip-compressed; a holder that does not know the packed form refuses it, naming that it holds no request object
 	Request any `json:"request"`
 }
 

contracts/go/seats/nodebuildnode/contract.go

@@ -485,7 +485,7 @@ type StepAskCompose struct {
 	Fetch   Fetch  `json:"fetch"`
 	Package string `json:"package"`
 	Reader  string `json:"reader,omitempty"`
-	// the compose-candidate request
+	// the compose-candidate request, in one of two forms: the request as a JSON object, or, for one near the bus's message limit, a JSON string "gzip+base64:" followed by the base64 of the request object gzip-compressed; a holder that does not know the packed form refuses it, naming that it holds no request object
 	Request any `json:"request"`
 }
 

contracts/parts/build-step.json

@@ -161,7 +161,7 @@
               "type": "string"
             },
             "request": {
-              "description": "the compose-candidate request"
+              "description": "the compose-candidate request, in one of two forms: the request as a JSON object, or, for one near the bus's message limit, a JSON string \"gzip+base64:\" followed by the base64 of the request object gzip-compressed; a holder that does not know the packed form refuses it, naming that it holds no request object"
             },
             "reader": {
               "type": "string"

contracts/ts/seats/nodebuildgo/src/parts/build-step.ts

@@ -293,7 +293,7 @@ export interface StepAskCompose {
   "fetch": Fetch;
   "package": string;
   "reader"?: string;
-  /** the compose-candidate request */
+  /** the compose-candidate request, in one of two forms: the request as a JSON object, or, for one near the bus's message limit, a JSON string "gzip+base64:" followed by the base64 of the request object gzip-compressed; a holder that does not know the packed form refuses it, naming that it holds no request object */
   "request": unknown;
 }
 

contracts/ts/seats/nodebuildimage/src/parts/build-step.ts

@@ -293,7 +293,7 @@ export interface StepAskCompose {
   "fetch": Fetch;
   "package": string;
   "reader"?: string;
-  /** the compose-candidate request */
+  /** the compose-candidate request, in one of two forms: the request as a JSON object, or, for one near the bus's message limit, a JSON string "gzip+base64:" followed by the base64 of the request object gzip-compressed; a holder that does not know the packed form refuses it, naming that it holds no request object */
   "request": unknown;
 }
 

contracts/ts/seats/nodebuildnode/src/parts/build-step.ts

@@ -293,7 +293,7 @@ export interface StepAskCompose {
   "fetch": Fetch;
   "package": string;
   "reader"?: string;
-  /** the compose-candidate request */
+  /** the compose-candidate request, in one of two forms: the request as a JSON object, or, for one near the bus's message limit, a JSON string "gzip+base64:" followed by the base64 of the request object gzip-compressed; a holder that does not know the packed form refuses it, naming that it holds no request object */
   "request": unknown;
 }
 

modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main.go

@@ -378,7 +378,7 @@ func RequestTools(r check.StateRead) []stdio.Tool {
 		Description: "The composition request a check sent to a node: the composer's whole input for that node (the node-engine's composition input, the case's " +
 			"manifests and verdicts, the seat list), kept exactly as sent so a session reproduces the check's composition (the composer run by hand over the same " +
 			"request gives the check's answer). Kept in the checker's state compositions, per check key (group.heads, the 12-digit heads hash) and node, " +
-			"about 430 KB each (kept compressed, so a value fits the state's 256 KiB), for 3 days (the state's ttl-seconds). With a check and a node, that request whole; with a check, " +
+			"0.7 to 0.8 MB each (kept compressed, in pieces that each fit the state's 256 KiB value), for 3 days (the state's ttl-seconds). With a check and a node, that request whole; with a check, " +
 			"the nodes it kept one for; with neither, every kept request, each with its size, digest and when it was kept. Read-only.",
 		Input: map[string]any{"type": "object", "properties": map[string]any{
 			"check": map[string]any{"type": "string", "description": "the check's key, <group>.<heads hash>, as the verdict and composition name it"},

modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main_test.go

@@ -5,6 +5,7 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"errors"
+	"math/rand"
 	"os"
 	"regexp"
 	"slices"
@@ -48,7 +49,36 @@ func TestTheToolsServedAreTheFiveReadTools(t *testing.T) {
 			t.Fatal(err)
 		}
 	}
+	// Issue 1966: a request whose compressed bytes pass the state's value limit is kept in pieces and read back whole; the
+	// pieces are no requests in the list.
+	rnd := make([]byte, 600<<10)
+	_, _ = rand.New(rand.NewSource(1)).Read(rnd)
+	big := []byte(`{"input":"` + base64.StdEncoding.EncodeToString(rnd) + `"}`)
+	if err := keeper.Keep(context.Background(), "big.0123456789ab", "anchor", big); err != nil {
+		t.Fatalf("a request of %d bytes: %v", len(big), err)
+	}
 	rt := RequestTools(check.StateRead{Keys: store.Keys, Get: store.Get})
+	if one, err := rt[0].Run(map[string]any{"check": "big.0123456789ab", "node": "anchor"}); err != nil || !strings.Contains(func() string { b, _ := json.Marshal(one); return string(b) }(), base64.StdEncoding.EncodeToString(rnd)[:64]) {
+		t.Errorf("the big request read back: %v", err)
+	}
+	// Listing reads no piece, and a request of another version is refused by name.
+	store.vals["v1.0123456789ab/anchor"] = json.RawMessage(`{"v":1,"check":"v1.0123456789ab","node":"anchor","gzip":"x"}`)
+	noPieces := check.StateRead{Keys: store.Keys, Get: func(k string) (json.RawMessage, error) {
+		if strings.HasPrefix(k, "pieces/") {
+			return nil, errors.New("a piece was read")
+		}
+		return store.Get(k)
+	}}
+	if _, err := RequestTools(noPieces)[0].Run(map[string]any{}); err != nil {
+		t.Errorf("listing: %v", err)
+	}
+	if _, err := rt[0].Run(map[string]any{"check": "v1.0123456789ab", "node": "anchor"}); err == nil || !strings.Contains(err.Error(), "version 1") {
+		t.Errorf("a version 1 request: %v", err)
+	}
+	delete(store.vals, "v1.0123456789ab/anchor")
+	if all, _ := rt[0].Run(map[string]any{}); strings.Count(func() string { b, _ := json.Marshal(all); return string(b) }(), `"node"`) != 4 {
+		t.Errorf("the list holds a piece as a request: %v", all)
+	}
 	if len(rt) != 1 || rt[0].Name != check.RequestsReadTool || !strings.Contains(rt[0].Description, "composition request a check sent to a node") {
 		t.Fatalf("request tools = %+v", rt)
 	}
@@ -312,6 +342,9 @@ func TestTheTryToolsAskAndReadATry(t *testing.T) { // ADR 0501 §5, the agreed i
 type memPut struct{ m *memStore }
 
 func (p memPut) Put(_ context.Context, key string, value []byte) (uint64, error) {
+	if len(value) > 262144 { // the state's value limit, headers included (issue 1966)
+		return 0, errors.New("the value is over the 262144 bytes the bucket takes")
+	}
 	p.m.vals[key] = value
 	return 1, nil
 }

modules/mesh-delivery-checker/internal/check/engines.go

@@ -228,6 +228,10 @@ func (e EngineCompositions) inSandbox(ctx context.Context, c *Case, head, node s
 	}
 	job := buildstep.ComposeJob{Fetch: buildstep.Fetch{Repository: nodeEngineRepo, Commit: head, Packages: packagesFor(e.Published, c, c.Tagged, nodeEngineRepo)}, Dir: meshcatalogclient.RootPath,
 		Package: composer.Package, Request: raw, Reader: "the node-engine head of " + c.Group}
+	// The ask travels on the bus, whose message limit a whole request passes (1.2 MB for a large node): it goes packed.
+	if err := job.PackRequest(raw); err != nil {
+		return a, err
+	}
 	verdict, err := e.Sandbox.Compose(ctx, job)
 	if err != nil {
 		return a, fmt.Errorf("the composer at the node-engine's head %s did not answer for %s: %w", head, node, err)

modules/mesh-delivery-checker/internal/check/engines_test.go

@@ -59,7 +59,11 @@ type fakeSandbox struct {
 
 func (f *fakeSandbox) Compose(_ context.Context, job buildstep.ComposeJob) (composer.Verdict, error) {
 	var req composer.Request
-	if err := json.Unmarshal(job.Request, &req); err != nil {
+	body, err := job.RequestBytes()
+	if err != nil {
+		return composer.Verdict{}, err
+	}
+	if err := json.Unmarshal(body, &req); err != nil {
 		return composer.Verdict{}, err
 	}
 	f.mu.Lock()
@@ -206,7 +210,11 @@ func TestTheCompositionIsMadeFromTheEnginesAnswers(t *testing.T) {
 		}
 		job := sb.jobs[0]
 		var req composer.Request
-		_ = json.Unmarshal(job.Request, &req)
+		if len(job.Request) == 0 || job.Request[0] != '"' {
+			t.Errorf("the request went whole, not packed (issue 1966): %.60s", job.Request)
+		}
+		body, _ := job.RequestBytes()
+		_ = json.Unmarshal(body, &req)
 		if job.Fetch.Repository != nodeEngineRepo || job.Fetch.Commit != head2 || job.Package != composer.Package ||
 			string(req.Input) != `{"nodes":[{"name":"anchor"}]}` || req.Cases[0].Manifests["web"].Digest == "" ||
 			len(req.Seats) != 1 || string(req.Seats[0]) != string(host.Seats[0]) {
@@ -220,8 +228,9 @@ func TestTheCompositionIsMadeFromTheEnginesAnswers(t *testing.T) {
 			t.Fatal(err)
 		}
 		keyOfHost, _ := nodeengineclient.CompositionKey(host.Group, host.Heads)
+		lastBody, _ := sb.jobs[len(sb.jobs)-1].RequestBytes()
 		got, err := ReadRequests(store.read(), keyOfHost, "anchor")
-		if b, _ := json.Marshal(got); err != nil || !strings.Contains(string(b), `"request":`+string(sb.jobs[len(sb.jobs)-1].Request)) {
+		if b, _ := json.Marshal(got); err != nil || !strings.Contains(string(b), `"request":`+string(lastBody)) {
 			t.Errorf("kept %s, %v: want the request of the last job under %s/anchor", b, err, keyOfHost)
 		}
 		store.err = errors.New("the state is full")
@@ -311,7 +320,8 @@ func TestTheCompositionIsMadeFromTheEnginesAnswers(t *testing.T) {
 			t.Fatalf("jobs %+v: want one job at the node-engine's trunk", sb.jobs)
 		}
 		var req composer.Request
-		_ = json.Unmarshal(sb.jobs[0].Request, &req)
+		b0, _ := sb.jobs[0].RequestBytes()
+		_ = json.Unmarshal(b0, &req)
 		if got := string(req.Cases[0].Verdicts["mesh-build-go"]); got != string(brings.Judged["mesh-build-go"]) || len(req.Cases[0].Verdicts) != 2 {
 			t.Errorf("the request's verdicts %s: want the check's judge's for mesh-build-go and the indexer's for mail", req.Cases[0].Verdicts)
 		}
@@ -321,7 +331,8 @@ func TestTheCompositionIsMadeFromTheEnginesAnswers(t *testing.T) {
 			t.Fatal(err)
 		}
 		var none composer.Request
-		_ = json.Unmarshal(sb.jobs[len(sb.jobs)-1].Request, &none)
+		bn, _ := sb.jobs[len(sb.jobs)-1].RequestBytes()
+		_ = json.Unmarshal(bn, &none)
 		if _, kept := none.Cases[0].Verdicts["mesh-build-go"]; kept {
 			t.Errorf("the running indexer's verdict on the change's manifest was kept: %s", none.Cases[0].Verdicts)
 		}

modules/mesh-delivery-checker/internal/check/requests.go

@@ -20,20 +20,28 @@ import (
 // session reproduces a check's composition exactly. The checker is a foundation part (novox/hq ADR 0619 §1-3), so its
 // kept data is a section of its manifest's old form, here `state`, and not an object store asked in `requires`.
 //
-// **What bounds it.** A request is the node-engine's whole composition input of one node, about 430 KB as JSON. A
-// state's value holds at most 256 KiB (kvlimit.ModuleStateValueBytes), so it is kept gzip-compressed (JSON shrinks about
-// tenfold) in a document of its own; a request whose compressed bytes still do not fit is refused by the put, which
-// fails the node's composition naming the size (never dropped). The manifest's ttl-seconds is its lifetime (3 days):
-// the bus drops a value past it, so nothing waits on a timer here. A check kept again overwrites the key.
+// **What bounds it.** A request is the node-engine's whole composition input of one node, 0.7 to 0.8 MB as JSON and
+// growing with the mesh. A state's value holds at most 256 KiB (kvlimit.ModuleStateValueBytes, headers included), and
+// the compressed request already passed it (issue 1966: 300127 bytes), so it is kept gzip-compressed in pieces: the key
+// of the check and node holds a small document naming the request's digest, size and number of pieces, and each piece is
+// a value of its own under RequestChunkKey, of at most RequestChunkBytes. The kept data is the checker's, a foundation
+// part's, so it stays in the old section `state` (ADR 0619 §2) and is read through the tool runner's state read, which
+// serves no object store of the old sections. The manifest's ttl-seconds is the lifetime (3 days) of the pointer and of
+// every piece: the bus drops a value past it, so nothing waits on a timer here. A check kept again overwrites the key;
+// a request whose pieces cannot all be put is refused naming the size (never dropped, never half kept: the pointer is
+// put after its pieces).
 const (
 	// RequestsStateName is the checker's state of kept requests and RequestsBucket its bucket.
 	RequestsStateName = "compositions"
 	RequestsBucket    = CheckerModule + "_" + RequestsStateName
 	// RequestsReadTool is the tool that reads a kept request.
 	RequestsReadTool = "checker_composition_requests"
+	// RequestChunkBytes is the most compressed bytes one piece holds: base64 of it, in its document, stays well under
+	// the state's 256 KiB value.
+	RequestChunkBytes = 128 << 10
 )
 
-// KeptRequest is a request as the state holds it: whose it is, and the request's JSON, compressed.
+// KeptRequest is the pointer to a request as the state holds it: whose it is, and what its pieces make.
 type KeptRequest struct {
 	V      int       `json:"v"`
 	Check  string    `json:"check"`
@@ -42,8 +50,32 @@ type KeptRequest struct {
 	// Size and Digest are the request's, uncompressed: its bytes and their sha256.
 	Size   int    `json:"size"`
 	Digest string `json:"digest"`
-	// Gzip is the request's bytes, gzip-compressed and base64-encoded.
-	Gzip string `json:"gzip"`
+	// Pieces is how many pieces (RequestChunkKey of the digest, 0 to Pieces-1) make the request's gzip bytes.
+	Pieces int `json:"pieces"`
+}
+
+// KeptPiece is one piece of a request's gzip bytes, base64-encoded.
+type KeptPiece struct {
+	V      int    `json:"v"`
+	Digest string `json:"digest"`
+	Index  int    `json:"index"`
+	Gzip   string `json:"gzip"`
+}
+
+// isPieceKey is whether a key is a piece's: under pieces/ and a sha256 digest, which no check's key (group.heads/node) is.
+func isPieceKey(k string) bool {
+	rest, ok := strings.CutPrefix(k, "pieces/")
+	if !ok {
+		return false
+	}
+	digest, _, _ := strings.Cut(rest, "/")
+	return len(digest) == 64
+}
+
+// RequestChunkKey is the key of a request's piece: under the request's digest, so a request kept again for the same
+// bytes writes the same pieces.
+func RequestChunkKey(digest string, index int) string {
+	return fmt.Sprintf("pieces/%s/%d", digest, index)
 }
 
 // RequestKey is the key a check's request to a node is kept under: the check's key (group.heads) and the node.
@@ -75,14 +107,28 @@ func (k RequestKeeper) Keep(ctx context.Context, key, node string, body []byte)
 		now = k.Now
 	}
 	sum := sha256.Sum256(body)
-	doc, err := json.Marshal(KeptRequest{V: 1, Check: key, Node: node, KeptAt: now().UTC(), Size: len(body),
-		Digest: hex.EncodeToString(sum[:]), Gzip: base64.StdEncoding.EncodeToString(packed.Bytes())})
+	digest := hex.EncodeToString(sum[:])
+	pieces := (packed.Len() + RequestChunkBytes - 1) / RequestChunkBytes
+	fail := func(err error) error {
+		return fmt.Errorf("the composition request of check %s to %s (%d bytes, %d compressed in %d pieces) could not be kept in the state %s: %w",
+			key, node, len(body), packed.Len(), pieces, RequestsStateName, err)
+	}
+	for i := 0; i < pieces; i++ {
+		end := min((i+1)*RequestChunkBytes, packed.Len())
+		doc, err := json.Marshal(KeptPiece{V: 2, Digest: digest, Index: i, Gzip: base64.StdEncoding.EncodeToString(packed.Bytes()[i*RequestChunkBytes : end])})
+		if err != nil {
+			return err
+		}
+		if _, err := k.Store.Put(ctx, RequestChunkKey(digest, i), doc); err != nil {
+			return fail(err)
+		}
+	}
+	doc, err := json.Marshal(KeptRequest{V: 2, Check: key, Node: node, KeptAt: now().UTC(), Size: len(body), Digest: digest, Pieces: pieces})
 	if err != nil {
 		return err
 	}
 	if _, err := k.Store.Put(ctx, RequestKey(key, node), doc); err != nil {
-		return fmt.Errorf("the composition request of check %s to %s (%d bytes, %d compressed) could not be kept in the state %s: %w",
-			key, node, len(body), packed.Len(), RequestsStateName, err)
+		return fail(err)
 	}
 	return nil
 }
@@ -104,7 +150,7 @@ func ReadRequests(s StateRead, key, node string) (any, error) {
 		if len(raw) == 0 {
 			return nil, fmt.Errorf("no composition request of check %s to %s is kept (none was sent, or it is past its lifetime)", key, node)
 		}
-		kept, body, err := unpackRequest(raw)
+		kept, body, err := unpackRequest(s, raw)
 		if err != nil {
 			return nil, fmt.Errorf("the kept request %s: %w", RequestKey(key, node), err)
 		}
@@ -120,6 +166,9 @@ func ReadRequests(s StateRead, key, node string) (any, error) {
 		if key != "" && !strings.HasPrefix(k, key+"/") {
 			continue
 		}
+		if isPieceKey(k) {
+			continue // a piece of a request, not a request: never read here
+		}
 		raw, err := s.Get(k)
 		if err != nil {
 			return nil, err
@@ -134,15 +183,30 @@ func ReadRequests(s StateRead, key, node string) (any, error) {
 	return map[string]any{"kept": listed}, nil
 }
 
-// unpackRequest reads a kept document and its request's bytes, which must match the digest they were kept with.
-func unpackRequest(raw []byte) (KeptRequest, []byte, error) {
+// unpackRequest reads a kept pointer's pieces and the request's bytes, which must match the digest they were kept with.
+func unpackRequest(s StateRead, raw []byte) (KeptRequest, []byte, error) {
 	var kept KeptRequest
 	if err := json.Unmarshal(raw, &kept); err != nil {
 		return kept, nil, fmt.Errorf("is no kept request: %w", err)
 	}
-	packed, err := base64.StdEncoding.DecodeString(kept.Gzip)
-	if err != nil {
-		return kept, nil, fmt.Errorf("holds no base64: %w", err)
+	if kept.V != 2 {
+		return kept, nil, fmt.Errorf("is a kept request of version %d, which this reader does not read (it reads version 2; an older one is past its lifetime within 3 days)", kept.V)
+	}
+	var packed []byte
+	for i := 0; i < kept.Pieces; i++ {
+		raw, err := s.Get(RequestChunkKey(kept.Digest, i))
+		if err != nil {
+			return kept, nil, err
+		}
+		var piece KeptPiece
+		if err := json.Unmarshal(raw, &piece); err != nil || len(raw) == 0 {
+			return kept, nil, fmt.Errorf("lacks its piece %d of %d (past its lifetime, or never kept)", i, kept.Pieces)
+		}
+		part, err := base64.StdEncoding.DecodeString(piece.Gzip)
+		if err != nil {
+			return kept, nil, fmt.Errorf("holds no base64 in its piece %d: %w", i, err)
+		}
+		packed = append(packed, part...)
 	}
 	zr, err := gzip.NewReader(bytes.NewReader(packed))
 	if err != nil {

sdk/buildstep/ask.go

@@ -1,8 +1,12 @@
 package buildstep
 
 import (
+	"bytes"
+	"compress/gzip"
+	"encoding/base64"
 	"encoding/json"
 	"fmt"
+	"io"
 	"path"
 	"slices"
 	"sort"
@@ -281,13 +285,55 @@ type CheckJob struct {
 
 // ComposeJob asks one compose-candidate build.
 type ComposeJob struct {
-	Fetch   Fetch           `json:"fetch"`
-	Dir     string          `json:"dir"`
-	Package string          `json:"package"`
+	Fetch   Fetch  `json:"fetch"`
+	Dir     string `json:"dir"`
+	Package string `json:"package"`
+	// Request is the composer's request: a JSON object, or a JSON string PackedRequestPrefix + the base64 of the object
+	// gzip-compressed (issue 1966; the checker packs every request it sends, and
+	// the part's `request` describes both forms). The part types it `any`, so both fit it; a
+	// build module that does not know the packed form refuses the ask naming that it holds no request object.
 	Request json.RawMessage `json:"request"`
 	Reader  string          `json:"reader,omitempty"`
 }
 
+// PackedRequestPrefix opens a compose job's request that travels gzip-compressed.
+const PackedRequestPrefix = "gzip+base64:"
+
+// PackRequest sets the job's request from the JSON object raw, packed.
+func (c *ComposeJob) PackRequest(raw []byte) error {
+	var b bytes.Buffer
+	zw := gzip.NewWriter(&b)
+	if _, err := zw.Write(raw); err != nil {
+		return err
+	}
+	if err := zw.Close(); err != nil {
+		return err
+	}
+	packed, err := json.Marshal(PackedRequestPrefix + base64.StdEncoding.EncodeToString(b.Bytes()))
+	c.Request = packed
+	return err
+}
+
+// RequestBytes is the job's request as a JSON object, unpacked when it travels packed.
+func (c ComposeJob) RequestBytes() ([]byte, error) {
+	var packed string
+	if len(c.Request) == 0 || c.Request[0] != '"' {
+		return c.Request, nil
+	}
+	if err := json.Unmarshal(c.Request, &packed); err != nil || !strings.HasPrefix(packed, PackedRequestPrefix) {
+		return nil, fmt.Errorf("buildstep: a compose job's request is a string that is no packed request")
+	}
+	raw, err := base64.StdEncoding.DecodeString(strings.TrimPrefix(packed, PackedRequestPrefix))
+	if err != nil {
+		return nil, fmt.Errorf("buildstep: the packed request of a compose job is no base64: %w", err)
+	}
+	zr, err := gzip.NewReader(bytes.NewReader(raw))
+	if err != nil {
+		return nil, fmt.Errorf("buildstep: the packed request of a compose job is no gzip: %w", err)
+	}
+	return io.ReadAll(zr)
+}
+
 // AskOf is any seat's ask (or this form) as the neutral StepAsk: the one conversion, since the three seats' types
 // are the part's one layout. A value that does not fit the layout is refused.
 func AskOf[T any](seatAsk T) (StepAsk, error) {
@@ -378,7 +424,11 @@ func (c ComposeJob) check(id string) error {
 	if c.Package == "" {
 		return fmt.Errorf("buildstep: the compose ask %s names no package to build", id)
 	}
-	if !json.Valid(c.Request) || len(c.Request) == 0 || c.Request[0] != '{' {
+	req, err := c.RequestBytes()
+	if err != nil {
+		return err
+	}
+	if !json.Valid(req) || len(req) == 0 || req[0] != '{' {
 		return fmt.Errorf("buildstep: the compose ask %s holds no request object", id)
 	}
 	return nil

sdk/buildstep/ask_test.go

@@ -144,6 +144,28 @@ func TestAskCheckAndRoundTrip(t *testing.T) {
 	if _, err := DecodeStepAsk([]byte(`{"v":2}`)); !errors.Is(err, ErrUnknownVersion) {
 		t.Errorf("another version: %v", err)
 	}
+	// Issue 1966: a compose job's request travels packed when it passes the bus's message limit, and reads back as sent.
+	t.Run("1966: a compose request travels packed", func(t *testing.T) {
+		obj := []byte(`{"v":1,"input":{"nodes":[]}}`)
+		job := ComposeJob{Fetch: Fetch{Repository: "novox/mesh-host", Commit: strings.Repeat("a", 40)}, Dir: ".", Package: "p"}
+		if err := job.PackRequest(obj); err != nil {
+			t.Fatal(err)
+		}
+		if got, err := job.RequestBytes(); err != nil || string(got) != string(obj) {
+			t.Errorf("read back %s, %v", got, err)
+		}
+		if err := job.check("ask"); err != nil {
+			t.Errorf("a packed request is refused: %v", err)
+		}
+		job.Request = json.RawMessage(`"not packed"`)
+		if err := job.check("ask"); err == nil {
+			t.Errorf("a string that is no packed request is accepted")
+		}
+		job.Request = obj
+		if got, err := job.RequestBytes(); err != nil || string(got) != string(obj) {
+			t.Errorf("a whole request read back %s, %v", got, err)
+		}
+	})
 }
 
 // The seat's value and the neutral form are the same JSON: AskOf takes any seat's type (here its shape, with a