ADR 0627 §2: a transfer read back from the bus takes its first chunk

A transfer is kept in a key-value state as JSON, and its empty Chunks map is omitted, so the one
read back for the first chunk had none and Take panicked: every publish in parts through
BusTransfers. The unit tests' transfers now round-trip JSON as the bus does. Found by the forge
module's whole test (CAT-G3).

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

go/go.sum

@@ -1,10 +1,13 @@
 github.com/antithesishq/antithesis-sdk-go v0.8.0-default-no-op h1:1BOWQJweNyvZMlpAHXGLiZQn9S+QXGcz3xh94lC0w6E=
+github.com/antithesishq/antithesis-sdk-go v0.8.0-default-no-op/go.mod h1:FQyySiasQQM8735Ddel3MRojmy4dA1IqCeyJ5jmPMbI=
 github.com/google/go-tpm v0.9.8 h1:slArAR9Ft+1ybZu0lBwpSmpwhRXaa85hWtMinMyRAWo=
 github.com/google/go-tpm v0.9.8/go.mod h1:h9jEsEECg7gtLis0upRBQU+GhYVH6jMjrFxI8u6bVUY=
 github.com/klauspost/compress v1.20.1 h1:T7kKElXUMXrUJ2E9QhQhxFtcK5rPyLdsGZvdbLMPdiQ=
+github.com/klauspost/compress v1.20.1/go.mod h1:LUdAzn7YLVvxLpc7y3V1m40wESHTgc1422pwwBSKYuI=
 github.com/minio/highwayhash v1.0.4 h1:asJizugGgchQod2ja9NJlGOWq4s7KsAWr5XUc9Clgl4=
 github.com/minio/highwayhash v1.0.4/go.mod h1:GGYsuwP/fPD6Y9hMiXuapVvlIUEhFhMTh0rxU3ik1LQ=
 github.com/nats-io/jwt/v2 v2.8.2 h1:XXRgB60MSTnqsRwejQurVDs/hcv2dkt+86GjI+I/bMc=
+github.com/nats-io/jwt/v2 v2.8.2/go.mod h1:Ag/56sq9OblL4JgdYufDd16Egb17Kr/8WwwuO/forVc=
 github.com/nats-io/nats-server/v2 v2.11.17 h1:GKEghcFK6A+aFx11Yf1LjgLC3txAwvyhnYzhBIQZA8I=
 github.com/nats-io/nats-server/v2 v2.11.17/go.mod h1:B1sFVz4StNosQ903ak4N1G01Fl/9f8e06mXpFIE2K24=
 github.com/nats-io/nats.go v1.54.0 h1:vsXoOxjHp/GmPUN+EcI7uOf/uB+iAP+kEsAFNQN0yzA=
@@ -19,3 +22,4 @@ golang.org/x/sys v0.21.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/sys v0.48.0 h1:bbX/i/6MgT9BVLM9RT1thmxL04yeTAhbEz4SyadbXoo=
 golang.org/x/sys v0.48.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
 golang.org/x/time v0.16.0 h1:vMb6ptszcQMkcwiRTAuNNU50gom6++Q/6gY2hDM6VDE=
+golang.org/x/time v0.16.0/go.mod h1:rVKOqvZeKvrDKTQiAHJ7wmwP0RzleSphoEA9RcdLA0s=

go/parts/receive.go

@@ -240,6 +240,10 @@ func (r *Receiver[M]) Take(id, opener, digest string, sequence int, last bool, d
 	if err := r.Objects.Put(r.chunkName(id, digest, sequence), data); err != nil {
 		return Received{}, fmt.Errorf("the objects did not take the chunk: %w", err)
 	}
+	// A transfer read back from a key-value state has no Chunks until one was taken: the empty map is kept omitted.
+	if t.Chunks == nil {
+		t.Chunks = map[string]int{}
+	}
 	t.Chunks[digest] = sequence + 1
 	t.Last = r.now()
 	if last {

go/parts/receive_test.go

@@ -3,6 +3,7 @@ package parts
 import (
 	"crypto/sha256"
 	"encoding/hex"
+	"encoding/json"
 	"errors"
 	"reflect"
 	"strings"
@@ -28,14 +29,31 @@ func (m memObjects) Used() (uint64, error) {
 	return u, nil
 }
 
-type memTransfers[M any] map[string]Transfer[M]
+// memTransfers keeps each transfer as the bus keeps it, its JSON, so every case reads back what a key-value state
+// gives (BusTransfers): an empty map kept with omitempty comes back nil.
+type memTransfers[M any] map[string][]byte
 
-func (m memTransfers[M]) Get(id string) (Transfer[M], bool, error) { t, ok := m[id]; return t, ok, nil }
+func (m memTransfers[M]) Get(id string) (Transfer[M], bool, error) {
-func (m memTransfers[M]) Put(t Transfer[M]) error                  { m[t.ID] = t; return nil }
+	var t Transfer[M]
-func (m memTransfers[M]) Delete(id string) error                   { delete(m, id); return nil }
+	raw, ok := m[id]
+	if !ok {
+		return t, false, nil
+	}
+	return t, true, json.Unmarshal(raw, &t)
+}
+func (m memTransfers[M]) Put(t Transfer[M]) error {
+	raw, err := json.Marshal(t)
+	m[t.ID] = raw
+	return err
+}
+func (m memTransfers[M]) Delete(id string) error { delete(m, id); return nil }
 func (m memTransfers[M]) List() ([]Transfer[M], error) {
 	var out []Transfer[M]
-	for _, t := range m {
+	for id := range m {
+		t, _, err := m.Get(id)
+		if err != nil {
+			return nil, err
+		}
 		out = append(out, t)
 	}
 	return out, nil