One push leaves the mesh consistent (issue 057)

A provision is minted while composing the consumer's node, and the
provider's grant list is a pure read of secrets already issued — so
pushing the consumer left the provider blind until somebody pushed it
again, with no signal to. A named push now captures what every machine
should be before composing, recomputes after, and sends the machines
whose declaration changed because of this push — by name, never
silently, converging over bounded rounds.

cmd/mesh-controller/push.go

@@ -9,6 +9,7 @@ import (
 	"flag"
 	"fmt"
 	"os"
+	"sort"
 	"strings"
 	"time"
 
@@ -249,6 +250,18 @@ func pushCommand(ctx context.Context, args []string) error {
 		return err
 	}
 
+	// What every machine should be BEFORE this push composes anything. Composing a named node
+	// mints the provisions its consumers need, and a minted provision changes what the PROVIDER
+	// machine should be — its grant list is a pure read of secrets already issued (novox/hq
+	// issue 057). Captured now so that, after the send, "what changed because of this push" is
+	// a comparison rather than a guess.
+	var before map[string]string
+	if len(args) == 1 {
+		if before, err = wouldSend(ctx, open, nodes); err != nil {
+			return err
+		}
+	}
+
 	server, err := link.Connect(nil, nil)
 	if err != nil {
 		return err
@@ -321,6 +334,41 @@ func pushCommand(ctx context.Context, args []string) error {
 	}
 	fmt.Printf("\n%d node(s) told\n", len(sending))
 
+	// **A push leaves the mesh consistent, not just the machine it named** (novox/hq issue 057).
+	// The machines whose declaration changed because of THIS push — providers a provision was
+	// just minted from — are sent theirs too, by name, never silently: the alternative was a
+	// consumer that retries forever while nothing says the provider was left blind, and a rule
+	// ("push the provider node too") enforced by nothing. Bounded: a cascade send may itself
+	// mint, so this converges over a few rounds, each naming what changed and why.
+	if len(args) == 1 && before != nil {
+		delivered := map[string]bool{args[0]: true}
+		for round := 0; round < 3; round++ {
+			after, err := wouldSend(ctx, open, nodes)
+			if err != nil {
+				return err
+			}
+			var also []string
+			for name, digest := range after {
+				if !delivered[name] && before[name] != "" && before[name] != digest {
+					also = append(also, name)
+				}
+			}
+			if len(also) == 0 {
+				break
+			}
+			sort.Strings(also)
+			fmt.Printf("\nthis push changed what %s should be — a provision granted from "+
+				"there; sending it too\n", strings.Join(also, ", "))
+			if err := sendTo(ctx, open, also); err != nil {
+				return err
+			}
+			for _, name := range also {
+				delivered[name] = true
+			}
+			before = after
+		}
+	}
+
 	// A named node is a request to make THAT node current now, so it waits for the node to say it
 	// applied exactly this. A whole-mesh or --behind push does not wait: it is a sweep, and blocking
 	// on the slowest machine would hold back the report on all the others.