Serve the read verbs on the serving controller's own connection, and name every connection

Each verb ran as a process that dialled the bus, so hundreds of short
connections an hour, all named mesh-controller, hid any client reconnecting
in a loop (hq issue 327). D15 now says a user whose connections keep dropping.

internal/broker/jetstream.go

@@ -28,6 +28,8 @@ import (
 type JetStream struct {
 	conn *nats.Conn
 	js   nats.JetStreamContext
+	// borrowed is a connection lent by its owner (Borrow): closing it is the owner's.
+	borrowed bool
 	// Note is how this says something it decided not to fail over. Nil is silent, which is only
 	// right for a caller that has no way to report; the controller sets it.
 	Note func(string, ...any)
@@ -40,9 +42,17 @@ func (j *JetStream) note(format string, args ...any) {
 	}
 }
 
+// ConnectionName is what a connection this process dials says it is, in the server's list of
+// connections: the controller's role and what it is doing (novox/hq issue 327). Every connection was
+// named `mesh-controller` — the serving controller's, each verb's own process, the build agents' — so the
+// server's list could not say which was which. The process sets it once, at its start; an option a
+// caller passes to Dial names one connection otherwise.
+var ConnectionName = "mesh-controller"
+
 // Dial connects and returns the controller's JetStream handle.
 func Dial(url string, opts ...nats.Option) (*JetStream, error) {
-	opts = append(opts, nats.Name("mesh-controller"), nats.Timeout(10*time.Second))
+	// The name first, so a name the caller gives is the one that stands.
+	opts = append([]nats.Option{nats.Name(ConnectionName), nats.Timeout(10 * time.Second)}, opts...)
 	// **Pinned, not named.** The bus presents the mesh's own certificate, which names nothing a
 	// public verifier would accept (design 25 §4: a host pins the server's exact certificate and
 	// checks nothing else, and so does this). Without this, the first connection failed with
@@ -130,11 +140,20 @@ func (j *JetStream) Conn() *nats.Conn { return j.conn }
 func (j *JetStream) Context() nats.JetStreamContext { return j.js }
 
 func (j *JetStream) Close() {
-	if j.conn != nil {
+	if j.conn != nil && !j.borrowed {
 		j.conn.Close()
 	}
 }
 
+// Borrow is the same connection for a caller that will close what it was handed when it is done: its
+// Close closes nothing, and the connection stays its owner's (novox/hq issue 327). How the serving
+// controller lends its own connection to work that would otherwise dial one of its own.
+func Borrow(j *JetStream) *JetStream {
+	lent := *j
+	lent.borrowed = true
+	return &lent
+}
+
 // EnsureStream creates the stream if it is absent and brings it to match if it is present.
 //
 // **Idempotent, because the controller asserts on every start** rather than creating once at

internal/broker/jetstream_test.go

@@ -3,6 +3,8 @@ package broker
 import (
 	"testing"
 
+	"github.com/nats-io/nats.go"
+
 	"github.com/novox/mesh-controller/internal/testbus"
 )
 
@@ -66,3 +68,32 @@ func TestAgainstARealServer(t *testing.T) {
 		}
 	})
 }
+
+// A connection says what it is in the server's list (novox/hq issue 327): the process's name, unless the
+// caller names this one; and a lent connection's Close leaves its owner's open.
+func TestAConnectionIsNamedAndALentOneIsNotClosed(t *testing.T) {
+	url := testbus.URL(t)
+	was := ConnectionName
+	ConnectionName = "mesh-controller verb conditions"
+	defer func() { ConnectionName = was }()
+	named, err := Dial(url)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer named.Close()
+	if got := named.Conn().Opts.Name; got != "mesh-controller verb conditions" {
+		t.Errorf("named %q", got)
+	}
+	lease, err := Dial(url, nats.Name("mesh-controller serving lease"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer lease.Close()
+	if got := lease.Conn().Opts.Name; got != "mesh-controller serving lease" {
+		t.Errorf("a name the caller gave became %q", got)
+	}
+	Borrow(named).Close()
+	if !named.Conn().IsConnected() {
+		t.Error("closing a lent connection closed its owner's")
+	}
+}

internal/link/builds_nats.go

@@ -47,6 +47,12 @@ func BuildsOverNATSOn(address, seat string) (Builders, error) {
 	return &natsBuilds{js: js, owned: true, seat: seat}, nil
 }
 
+// BuildsOn is the asking side on a connection the caller holds, which Close leaves open: the serving
+// controller asks on its own rather than dialling one per build (novox/hq issue 327).
+func BuildsOn(js *broker.JetStream, seat string) Builders {
+	return &natsBuilds{js: js, seat: seat}
+}
+
 // role is the seat asked: what the asker was made for, or the current build role for one made
 // without saying (a test building the struct by hand).
 func (b *natsBuilds) role() string {