Point the builder's package binding at the port given with --packages-port (hq ADR 0100)

internal/bootstrap/builder.go

@@ -1,8 +1,10 @@
 package bootstrap
 
 import (
+	"bytes"
 	"context"
 	"fmt"
+	"strconv"
 	"strings"
 )
 
@@ -53,6 +55,9 @@ func InstallBuilder(ctx context.Context, o Options, d Deps, control controlPlane
 			"This is the manifest that makes the builder an ordinary module. Without it the mesh "+
 			"has the image and no way to run it, so nothing can be built here", err)
 	}
+	if manifest, err = followPackagesPort(manifest, o.Ports.orDefaults().Packages); err != nil {
+		return out, err
+	}
 	pinned, places, err := pinPlaceholder(manifest, published.Reference, BuilderModule)
 	if err != nil {
 		return out, err
@@ -84,3 +89,25 @@ func InstallBuilder(ctx context.Context, o Options, d Deps, control controlPlane
 	out.Installed.Pushed, err = pushNode(ctx, o, control, say)
 	return out, err
 }
+
+// packagesPortInBinding is the package registry's port as the builder's manifest names it, in the
+// binding file it carries — JSON inside a JSON string, so its quotes are escaped.
+const packagesPortInBinding = `\"port\": 3000`
+
+// followPackagesPort points the builder's package binding at the port the node gave the package
+// registry (novox/hq ADR 0100). Genesis raises the registry by hand before gitea is a module, so no
+// binding the controller resolves can say where it is; the builder carries the address in its own
+// manifest, and a port given at genesis must reach it there or the base build dials a port nothing
+// answers on. At the default it is left byte for byte as the catalogue has it.
+func followPackagesPort(manifest []byte, port int) ([]byte, error) {
+	if port == defaultGiteaPort {
+		return manifest, nil
+	}
+	if n := bytes.Count(manifest, []byte(packagesPortInBinding)); n != 1 {
+		return nil, fmt.Errorf("the builder's manifest names the package registry's port %d time(s) where "+
+			"this installer looks for it once (%s), so the port given with --packages-port cannot reach "+
+			"it; nothing was changed", n, packagesPortInBinding)
+	}
+	return bytes.Replace(manifest, []byte(packagesPortInBinding),
+		[]byte(`\"port\": `+strconv.Itoa(port)), 1), nil
+}