internal/pkg: hold artifact in DCE

This is significantly slower but enables much better error reporting.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/exec_test.go

@@ -11,7 +11,6 @@ import (
 	"path/filepath"
 	"slices"
 	"testing"
-	"unique"
 
 	"hakurei.app/check"
 	"hakurei.app/container"
@@ -50,6 +49,13 @@ func TestExec(t *testing.T) {
 		"check": {Mode: 0400, Data: []byte{0}},
 	}
 	wantOfflineEncode := pkg.Encode(wantOffline.hash())
+	failingArtifact := &stubArtifact{
+		kind:   pkg.KindTar,
+		params: []byte("doomed artifact"),
+		cure: func(t *pkg.TContext) error {
+			return stub.UniqueError(0xcafe)
+		},
+	}
 
 	checkWithCache(t, []cacheTestCase{
 		{"offline", pkg.CValidateKnown | checkDestroySubstitutes, nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
@@ -86,18 +92,10 @@ func TestExec(t *testing.T) {
 					check.MustAbs("/opt/bin/testtool"),
 					[]string{"testtool"},
 
-					pkg.MustPath("/proc/nonexistent", false, &stubArtifact{
-						kind:   pkg.KindTar,
-						params: []byte("doomed artifact"),
-						cure: func(t *pkg.TContext) error {
-							return stub.UniqueError(0xcafe)
-						},
-					}),
+					pkg.MustPath("/proc/nonexistent", false, failingArtifact),
 				), nil, nil, &pkg.DependencyCureError{
 					{
-						Ident: unique.Make(pkg.ID(pkg.MustDecode(
-							"Sowo6oZRmG6xVtUaxB6bDWZhVsqAJsIJWUp0OPKlE103cY0lodx7dem8J-qQF0Z1",
-						))),
+						A:   failingArtifact,
 						Err: stub.UniqueError(0xcafe),
 					},
 				}},