The Go seat goes on to the public proxy only on a 404, the public proxy to direct on any failure (issue 1966, review 1)

Claude-Session: https://claude.ai/code/session_01JG73KEq4zoDfM9WtYpcQgZ

modules/mesh-build-go/cmd/mesh-build-go/fetch.go

@@ -334,10 +334,11 @@ func (m *Module) goEnv() []string {
 		// The Go seat first, the public proxy second, the forge's git last (CAT-BG3, E11: direct goes in the first
 		// change after mesh-sdk's and mesh-contracts' first numbered versions are in the Go seat); no GOPRIVATE, and
 		// the checksum database off for the forge's paths, which go.sum and the builder's h1: digest guard instead.
-		// The separator is "|", not ",": with "," go goes on only after a 404 or 410, so a seat that does not hold a
-		// package (a contracts package not published yet) and a public proxy the node cannot reach stopped the fetch
-		// before "direct" (issue 1966); with "|" any failure goes on to the next, and direct reaches the forge's git.
-		env = append(env, "GOPROXY="+proxy+"|"+PublicGoProxy+"|direct", "GONOSUMDB="+ForgeGoPaths, "GOPRIVATE=")
+		// The seat goes on to the public proxy only on a 404 or 410 (",": a package it does not hold), so a seat that
+		// fails otherwise (5xx, refused, timeout) fails the fetch loudly; the public proxy goes on to direct on any
+		// failure ("|"): a public proxy the node cannot reach stopped the fetch before direct, and direct reaches the
+		// forge's git for a package the seat does not hold (issue 1966, ADR 0605 §6).
+		env = append(env, "GOPROXY="+proxy+","+PublicGoProxy+"|direct", "GONOSUMDB="+ForgeGoPaths, "GOPRIVATE=")
 	} else {
 		env = append(env, "GOPRIVATE="+ForgeGoPaths)
 	}

modules/mesh-build-go/cmd/mesh-build-go/fetch_test.go

@@ -153,7 +153,7 @@ func TestFetchAsksGitForTheSshRemoteAndDownloadsEachModule(t *testing.T) {
 	}
 	m.GoSeatFile = seat
 	env := strings.Join(m.goEnv(), " ")
-	for _, want := range []string{"GOPROXY=http://forge.mesh:3000/api/packages/novox/go|https://proxy.golang.org|direct", "GONOSUMDB=git.novox.be", "GOPRIVATE= "} {
+	for _, want := range []string{"GOPROXY=http://forge.mesh:3000/api/packages/novox/go,https://proxy.golang.org|direct", "GONOSUMDB=git.novox.be", "GOPRIVATE= "} {
 		if !strings.Contains(env+" ", want) {
 			t.Errorf("with the Go seat bound the environment lacks %q: %s", want, env)
 		}