Item 4 (join 11): the composition-inputs test guards what each machine was asked

gather asks the machines side by side, and the test's stand-in call wrote one map from each of them: a concurrent map
write, the panic once seen at compositioninputs_test.go:61 (the race detector shows it every run). The record is
guarded; the whole assigner's unit suite runs clean under the race detector.

Builds: design 47 G §354, A-243, A-252

Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/compositioninputs_test.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"errors"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -55,10 +56,14 @@ func TestTheMachinesOfAStep(t *testing.T) {
 // §354, A-243, A-252, §64: each machine is asked compose-candidate with the step's key and input true, its numbers as written; a
 // silent or unready node says why, and a machine away is not asked.
 func TestAStepsInputsAreAskedOfEachMachine(t *testing.T) {
+	// gather asks the machines side by side, so the record of what each was asked is guarded.
+	var mu sync.Mutex
 	asked := map[string]string{}
 	call := func(node, key string, body any) (json.RawMessage, error) {
 		raw, _ := json.Marshal(body)
+		mu.Lock()
 		asked[node] = key + " " + string(raw)
+		mu.Unlock()
 		switch node {
 		case "g14":
 			return nil, errors.New("no responders")