internal/pkg: implement exec artifact

This runs a program in a container environment. Artifacts can be made available to the container, they are cured concurrently and mounted in order.

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

internal/pkg/pkg_test.go

@@ -23,6 +23,8 @@ import (
 	"hakurei.app/internal/pkg"
 )
 
+func TestMain(m *testing.M) { container.TryArgv0(nil); os.Exit(m.Run()) }
+
 // overrideIdent overrides the ID method of [Artifact].
 type overrideIdent struct {
 	id pkg.ID
@@ -251,13 +253,16 @@ type cureStep struct {
 	err      error
 }
 
+// ignorePathname is passed to cureMany to skip the pathname check.
+var ignorePathname = check.MustAbs("/\x00")
+
 // cureMany cures many artifacts against a [Cache] and checks their outcomes.
 func cureMany(t *testing.T, c *pkg.Cache, steps []cureStep) {
 	for _, step := range steps {
 		t.Log("cure step:", step.name)
 		if pathname, checksum, err := c.Cure(step.a); !reflect.DeepEqual(err, step.err) {
 			t.Fatalf("Cure: error = %v, want %v", err, step.err)
-		} else if !pathname.Is(step.pathname) {
+		} else if step.pathname != ignorePathname && !pathname.Is(step.pathname) {
 			t.Fatalf("Cure: pathname = %q, want %q", pathname, step.pathname)
 		} else if checksum != step.checksum {
 			t.Fatalf("Cure: checksum = %s, want %s", pkg.Encode(checksum), pkg.Encode(step.checksum))