The builder narrates every step, and every command it runs

A build was silent from clone to publish, so a build in progress, one that failed
quietly, and a request that never arrived all looked identical — which cost a long
diagnosis against a running mesh chasing "the handler never fired".

Now: the handler announces a request the instant it lands. Build logs each phase
— clone, commit, manifest, bases, each artifact starting and finishing with what
it produced, resolve, done — through a Log callback that is nil-safe, so the tests
that pass none still build. And the Command runner echoes every command before it
runs, with where and how long it took, because on a hang the last line is exactly
the command it is stuck inside: "git clone waiting on a network that will not
answer" rather than "the builder did nothing".

The unreadable-request path prints to stdout now too, not stderr, so it shows in
docker logs without splitting streams — the split is what hid it.

Claude-Session: https://claude.ai/code/session_01D6qtiYU3P9jk3pnAXyAFyx

cmd/mesh-builder/main.go

@@ -160,12 +160,18 @@ func run() error {
 func answer(ctx context.Context, channel *amqp.Channel, publisher builder.Publisher,
 	on, workspace string, delivery amqp.Delivery) {
 
+	// **First thing, and to stdout.** A build request that arrives and produces no visible line
+	// until it either finishes or fails is indistinguishable from one that never arrived — which
+	// cost a long diagnosis against a running mesh, chasing "the handler never fired" when the
+	// truth was only that the handler said nothing until the end.
+	fmt.Printf("a build request arrived (%d bytes)\n", len(delivery.Body))
+
 	var request link.BuildRequest
 	if err := json.Unmarshal(delivery.Body, &request); err != nil {
 		// Unreadable. Acknowledged and dropped rather than requeued: a message this builder
 		// cannot parse will not become parseable by being delivered again, and requeueing it
 		// would put it in front of every real request for ever.
-		fmt.Fprintf(os.Stderr, "a request could not be read and was dropped: %v\n", err)
+		fmt.Printf("a request could not be read and was dropped: %v\n", err)
 		_ = delivery.Ack(false)
 		return
 	}
@@ -184,7 +190,10 @@ func answer(ctx context.Context, channel *amqp.Channel, publisher builder.Publis
 	fmt.Println()
 
 	built, err := builder.Build(ctx, builder.Command, publisher,
-		request.Repository, request.Path, request.Ref, workspace, request.Held)
+		request.Repository, request.Path, request.Ref, workspace, request.Held,
+		func(step, message string) {
+			fmt.Printf("  [%s] %s\n", step, message)
+		})
 	if err != nil {
 		// A failure is a result. A build that fails and says nothing is indistinguishable from a
 		// builder that is not running, and those want completely different responses.

cmd/mesh-builder/once.go

@@ -84,7 +84,8 @@ func buildOnce(ctx context.Context, args []string) error {
 	}
 	fmt.Fprintln(os.Stderr)
 
-	built, buildErr := builder.Build(ctx, builder.Command, publisher, repository, *path, *ref, where, bases)
+	built, buildErr := builder.Build(ctx, builder.Command, publisher, repository, *path, *ref, where, bases,
+		func(step, message string) { fmt.Printf("  [%s] %s\n", step, message) })
 	if buildErr != nil {
 		return buildErr
 	}