Carry mesh package versions in build asks and fingerprints

ADR 0573 §2 has every module build against the latest published version of
each mesh package it uses, chosen by the planner and written by the build,
never pinned by hand (issue 1585, S4). The ask, the fetch request and the
merge preview now carry the packages and their versions, and the new-form
fingerprint takes each version, so a package's trunk merge changes every
dependent's fingerprint. A module using no package keeps its fingerprint.

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

go/buildstep/request_test.go

@@ -10,11 +10,15 @@ import (
 // from the indexer's kept inputs and the build module reads them from the call, never from the manifest (ADR 0495
 // clause 1). The request survives the trip through a tool call's arguments.
 func TestAFetchRequestCarriesTheNamedPathsThroughTheToolCall(t *testing.T) {
+	// And the versions of the mesh packages to build against (novox/hq ADR 0573 §2; issue 1585 S4).
 	req := FetchRequest{Repository: "novox/mesh-sdk", Commit: strings.Repeat("a", 40), Ref: "refs/pull/7/head",
-		Dir: ".", Paths: []string{"package.json", "src"}}
+		Dir: ".", Paths: []string{"package.json", "src"}, Packages: map[string]string{"git.novox.be/novox/mesh-sdk/go": strings.Repeat("d", 40)}}
 	args := req.Args()
-	// A tool call's arguments arrive as JSON: lists of any.
+	// A tool call's arguments arrive as JSON: lists of any, objects of any.
 	args["paths"] = []any{"package.json", "src"}
+	if p, ok := args["packages"].(map[string]any); !ok || p["git.novox.be/novox/mesh-sdk/go"] != strings.Repeat("d", 40) {
+		t.Fatalf("the packages are not in the call's arguments: %v", args["packages"])
+	}
 	got, err := ParseFetchRequest(args)
 	if err != nil {
 		t.Fatal(err)
@@ -42,6 +46,9 @@ func TestAFetchRequestCarriesTheNamedPathsThroughTheToolCall(t *testing.T) {
 		{map[string]any{"dir": "../a", "paths": []any{"src"}}, "leaves the repository"},
 		{map[string]any{"dir": "modules/a", "paths": []any{3}}, "paths is a list of strings"},
 		{map[string]any{"dir": "modules/a"}, "names a module directory and no path"},
+		{map[string]any{"packages": map[string]any{"git.novox.be/novox/mesh-sdk/go": "v0.1.7"}}, "no full commit"},
+		{map[string]any{"packages": map[string]any{"a b": strings.Repeat("d", 40)}}, "no module path"},
+		{map[string]any{"packages": []any{"x"}}, "packages is an object"},
 	} {
 		args := map[string]any{}
 		for k, v := range ok {