One bus: the AMQP transport is gone from the controller

The mesh runs on the seat's bus alone (novox/hq ADR 0131, design 28 task 5.5). The old
transport's consume loop, build request, tool ask, management API and account scoping are
deleted, and the bus switch with them; the controller connects to the broker seat and to
nothing else. The store-window tests keep their assertions on a bus-less fake, and the tests
that only made sense for the old transport's in-memory holding go with it.

internal/link/build.go

@@ -1,12 +1,7 @@
 package link
 
 import (
-	"context"
 	"encoding/json"
-	"fmt"
-	"time"
-
-	amqp "github.com/rabbitmq/amqp091-go"
 )
 
 // Asking a machine to build a module, and hearing what came out.
@@ -22,21 +17,6 @@ import (
 // holds no opinion about what they contain, and a host that also built things would be a host
 // with a container runtime requirement and a git dependency (novox/hq ADR 0005).
 
-// BuildQueue is where build requests wait. One queue, so several build machines can share the
-// work and each request is done exactly once — which is what a queue is for and what a
-// per-machine routing key would not give.
-const BuildQueue = "builds"
-
-// KeyBuilt is what a builder publishes when it has finished, successfully or not.
-const KeyBuilt = "built"
-
-// ReplyQueue is where the answer to one request goes.
-//
-// **Named here rather than left to the broker**, so it can be scoped and reasoned about. A broker
-// generates its own name for an unnamed queue, and a builder permitted to write to whatever that
-// convention happens to produce works on one broker and silently cannot answer on another.
-func ReplyQueue(id string) string { return BuildQueue + ".reply." + id }
-
 // BuildRequest is one module to build.
 type BuildRequest struct {
 	// ID correlates the answer with the asking. Not the module name: two builds of one module can
@@ -118,77 +98,3 @@ type MadeArtifact struct {
 	Kind      string `json:"kind"`
 	Reference string `json:"reference"`
 }
-
-// RequestBuild asks for a module to be built and waits for the answer.
-//
-// Waiting rather than returning immediately, because the thing a person wants after asking for a
-// build is to know whether it worked. A build that is dispatched and forgotten needs somewhere to
-// look afterwards, and there is nowhere yet.
-func RequestBuild(ctx context.Context, channel *amqp.Channel, request BuildRequest,
-	timeout time.Duration) (BuildResult, error) {
-
-	// Its own queue for the answer, declared before the ask. Consuming from the shared exchange
-	// would mean competing with the control plane's own consumer for a message meant for this
-	// caller — which is the fault this package's own doc comment records having had.
-	replies, err := channel.QueueDeclare(ReplyQueue(request.ID), false, true, true, false, nil)
-	if err != nil {
-		return BuildResult{}, err
-	}
-	// Bound to the exchange, and the answer comes back through it.
-	//
-	// **A builder never publishes to the default exchange**, because permission there is per
-	// exchange and not per queue — a builder allowed to use it could publish into any node's
-	// queue, which is the privilege a build machine most obviously should not have. Found by
-	// running it: the builder built, could not answer, and the connection closed saying only
-	// "not allowed to publish to exchange ''".
-	//
-	// The cost is that every asker sees every result, which is why the correlation is checked
-	// below rather than assumed.
-	if err := channel.QueueBind(replies.Name, KeyBuilt, Exchange, false, nil); err != nil {
-		return BuildResult{}, err
-	}
-	answers, err := channel.ConsumeWithContext(ctx, replies.Name, "", true, true, false, false, nil)
-	if err != nil {
-		return BuildResult{}, err
-	}
-
-	body, err := json.Marshal(request)
-	if err != nil {
-		return BuildResult{}, err
-	}
-	if err := channel.PublishWithContext(ctx, "", BuildQueue, false, false, amqp.Publishing{
-		ContentType:   "application/json",
-		DeliveryMode:  amqp.Persistent,
-		CorrelationId: request.ID,
-		ReplyTo:       replies.Name,
-		Body:          body,
-	}); err != nil {
-		return BuildResult{}, err
-	}
-
-	waiting, cancel := context.WithTimeout(ctx, timeout)
-	defer cancel()
-	for {
-		select {
-		case <-waiting.Done():
-			return BuildResult{}, fmt.Errorf(
-				"no builder answered within %s. Something must be consuming %q, and nothing is "+
-					"— or it is building something that takes longer than this",
-				timeout, BuildQueue)
-		case delivery, ok := <-answers:
-			if !ok {
-				return BuildResult{}, fmt.Errorf("the connection closed while waiting for a build")
-			}
-			var result BuildResult
-			if err := json.Unmarshal(delivery.Body, &result); err != nil {
-				return BuildResult{}, fmt.Errorf("a builder answered with something unreadable: %w", err)
-			}
-			if result.ID != request.ID {
-				// Somebody else's answer on this queue. Ignored rather than returned, because
-				// returning it would attribute one build's outcome to another's.
-				continue
-			}
-			return result, nil
-		}
-	}
-}