Hold a node from composing to sending, so a push composed before converge or adopt is never sent after it (hq ADR 0100)

cmd/mesh-controller/hold.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"context"
+)
+
+// heldKey carries the nodes this call already holds, so an act that holds a node and then sends
+// through sendTo does not wait on itself.
+type heldKey struct{}
+
+// holdNodes holds the named nodes for composing and sending their declarations (novox/hq ADR
+// 0100), skipping any the context already holds, and returns a context that says it holds them.
+// Release gives back only what this call took.
+func holdNodes(ctx context.Context, open *stores, names []string) (context.Context, func(), error) {
+	already, _ := ctx.Value(heldKey{}).(map[string]bool)
+	var take []string
+	for _, n := range names {
+		if !already[n] {
+			take = append(take, n)
+		}
+	}
+	if len(take) == 0 {
+		return ctx, func() {}, nil
+	}
+	release, err := open.inventory.HoldNodes(ctx, take)
+	if err != nil {
+		return ctx, nil, err
+	}
+	held := map[string]bool{}
+	for n := range already {
+		held[n] = true
+	}
+	for _, n := range take {
+		held[n] = true
+	}
+	return context.WithValue(ctx, heldKey{}, held), release, nil
+}