internal/pkg: in-flight error resolution

The DCE is a slow and overcomplicated solution to a simple problem. This change replaces the DCE by resolving errors in-flight.

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

internal/pkg/exec_test.go

@@ -118,11 +118,8 @@ func TestExec(t *testing.T) {
 					[]string{"testtool"},
 
 					pkg.MustPath("/proc/nonexistent", false, failingArtifact),
-				), nil, nil, pkg.WNew, &pkg.DependencyCureError{
-					{
-						A:   failingArtifact,
-						Err: stub.UniqueError(0xcafe),
-					},
+				), nil, nil, pkg.WNew, pkg.InputError{
+					failingArtifact: stub.UniqueError(0xcafe),
 				}},
 
 				{"invalid paths", pkg.NewExec(