hakurei/internal/pkg/pkg_test.go

package pkg_test

import (
	"archive/tar"
	"bytes"
	"context"
	"crypto/sha512"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"reflect"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"testing"
	"testing/fstest"
	"time"
	"unique"
	"unsafe"

	"hakurei.app/check"
	"hakurei.app/container"
	"hakurei.app/fhs"
	"hakurei.app/internal/info"
	"hakurei.app/internal/landlock"
	"hakurei.app/internal/pkg"
	"hakurei.app/internal/stub"
	"hakurei.app/message"
)

var skipLock = func() pkg.CacheAttr {
	var attr pkg.CacheAttr
	*(*bool)(unsafe.Pointer(reflect.ValueOf(&attr).
		Elem().
		FieldByName("skipLock").
		UnsafeAddr())) = true
	return attr
}()

var (
	// extension is a string uniquely identifying a set of custom [Artifact]
	// implementations registered by calling [Register].
	//
	//go:linkname extension hakurei.app/internal/pkg.extension
	extension string

	// opened is false if [Open] was never called.
	//
	//go:linkname opened hakurei.app/internal/pkg.opened
	opened bool

	// irArtifact refers to artifact IR interpretation functions and must not be
	// written to directly.
	//
	//go:linkname irArtifact hakurei.app/internal/pkg.irArtifact
	irArtifact map[pkg.Kind]pkg.IRReadFunc

	// statusHeader is the header written to all status files in dirStatus.
	//
	//go:linkname statusHeader hakurei.app/internal/pkg.statusHeader
	statusHeader string
)

// newRContext returns the address of a new [pkg.RContext] unsafely created for
// the specified [testing.TB].
func newRContext(tb testing.TB, c *pkg.Cache) *pkg.RContext {
	var r pkg.RContext
	rContextVal := reflect.ValueOf(&r).Elem().FieldByName("ctx")
	reflect.NewAt(
		rContextVal.Type(),
		unsafe.Pointer(rContextVal.UnsafeAddr()),
	).Elem().Set(reflect.ValueOf(tb.Context()))
	rCacheVal := reflect.ValueOf(&r).Elem().FieldByName("cache")
	reflect.NewAt(
		rCacheVal.Type(),
		unsafe.Pointer(rCacheVal.UnsafeAddr()),
	).Elem().Set(reflect.ValueOf(c))
	return &r
}

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
	pkg.TrivialArtifact
}

func (a overrideIdent) ID() pkg.ID { return a.id }

// overrideIdentFile overrides the ID method of [FileArtifact].
type overrideIdentFile struct {
	id pkg.ID
	pkg.FileArtifact
}

func (a overrideIdentFile) ID() pkg.ID { return a.id }

// A knownIdentArtifact implements [pkg.KnownIdent] and [Artifact]
type knownIdentArtifact interface {
	pkg.KnownIdent
	pkg.TrivialArtifact
}

// A knownIdentFile implements [pkg.KnownIdent] and [FileArtifact]
type knownIdentFile interface {
	pkg.KnownIdent
	pkg.FileArtifact
}

// overrideChecksum overrides the Checksum method of [Artifact].
type overrideChecksum struct {
	checksum pkg.Checksum
	knownIdentArtifact
}

func (a overrideChecksum) Checksum() pkg.Checksum { return a.checksum }

// overrideChecksumFile overrides the Checksum method of [FileArtifact].
type overrideChecksumFile struct {
	checksum pkg.Checksum
	knownIdentFile
}

func (a overrideChecksumFile) Checksum() pkg.Checksum { return a.checksum }

// A stubArtifact implements [TrivialArtifact] with hardcoded behaviour.
type stubArtifact struct {
	kind   pkg.Kind
	params []byte
	deps   []pkg.Artifact

	cure func(t *pkg.TContext) error
}

func (a *stubArtifact) Kind() pkg.Kind             { return a.kind }
func (a *stubArtifact) Params(ctx *pkg.IContext)   { ctx.Write(a.params) }
func (a *stubArtifact) Inputs() []pkg.Artifact     { return a.deps }
func (a *stubArtifact) Cure(t *pkg.TContext) error { return a.cure(t) }
func (*stubArtifact) IsExclusive() bool            { return false }

// A stubArtifactF implements [FloodArtifact] with hardcoded behaviour.
type stubArtifactF struct {
	kind   pkg.Kind
	params []byte
	deps   []pkg.Artifact
	excl   bool

	cure func(f *pkg.FContext) error
}

func (a *stubArtifactF) Kind() pkg.Kind             { return a.kind }
func (a *stubArtifactF) Params(ctx *pkg.IContext)   { ctx.Write(a.params) }
func (a *stubArtifactF) Inputs() []pkg.Artifact     { return a.deps }
func (a *stubArtifactF) Cure(f *pkg.FContext) error { return a.cure(f) }
func (a *stubArtifactF) IsExclusive() bool          { return a.excl }

// A stubFile implements [FileArtifact] with hardcoded behaviour.
type stubFile struct {
	data []byte
	err  error

	stubArtifact
}

func (a *stubFile) Cure(*pkg.RContext) (io.ReadCloser, error) {
	return io.NopCloser(bytes.NewReader(a.data)), a.err
}

// newStubFile returns an implementation of [pkg.File] with hardcoded behaviour.
func newStubFile(
	kind pkg.Kind,
	id pkg.ID,
	sum *pkg.Checksum,
	data []byte,
	err error,
) pkg.FileArtifact {
	f := overrideIdentFile{id, &stubFile{data, err, stubArtifact{
		kind,
		nil,
		nil,
		func(*pkg.TContext) error {
			panic("unreachable")
		},
	}}}
	if sum == nil {
		return f
	} else {
		return overrideChecksumFile{*sum, f}
	}
}

// stubExtern implements [External] with hardcoded prepared outcomes.
type stubExtern struct {
	artifact map[unique.Handle[pkg.ID]]pkg.Checksum
	checksum map[unique.Handle[pkg.Checksum]]fstest.MapFS
	status   map[unique.Handle[pkg.ID]]string
}

func (e stubExtern) Artifact(_ context.Context, id unique.Handle[pkg.ID]) (*pkg.Checksum, error) {
	if checksum, ok := e.artifact[id]; ok {
		return &checksum, nil
	}
	return nil, nil
}

func (e stubExtern) Checksum(checksum unique.Handle[pkg.Checksum]) pkg.Artifact {
	var buf bytes.Buffer
	if err := pkg.Write(e.checksum[checksum], ".", &buf); err != nil {
		panic(err)
	}
	return pkg.NewArchive(pkg.NewFile("", buf.Bytes()))
}

func (e stubExtern) Status(_ *pkg.RContext, id unique.Handle[pkg.ID]) (io.ReadCloser, error) {
	if status, ok := e.status[id]; ok {
		return io.NopCloser(strings.NewReader(status)), nil
	}
	return nil, nil
}

// destroyArtifact removes all traces of an [Artifact] from the on-disk cache.
// Do not use this in a test case without a very good reason to do so.
func destroyArtifact(
	t *testing.T,
	base *check.Absolute,
	c *pkg.Cache,
	a pkg.Artifact,
) {
	if pathname, checksum, err := c.Cure(a); err != nil {
		t.Fatalf("Cure: error = %v", err)
	} else if err = os.Remove(pathname.String()); err != nil {
		t.Fatal(err)
	} else {
		p := base.Append(
			"checksum",
			pkg.Encode(checksum.Value()),
		)
		if err = filepath.WalkDir(p.String(), func(
			path string,
			d fs.DirEntry,
			err error,
		) error {
			if err != nil {
				return err
			}
			if d.IsDir() {
				return os.Chmod(path, 0700)
			}
			return nil
		}); err != nil && !errors.Is(err, os.ErrNotExist) {
			t.Fatal(err)
		}
		if err = os.RemoveAll(p.String()); err != nil {
			t.Fatal(err)
		}
	}
}

// newDestroyArtifactFunc returns a function that calls destroyArtifact.
func newDestroyArtifactFunc(a pkg.Artifact) func(
	t *testing.T,
	base *check.Absolute,
	c *pkg.Cache,
) {
	return func(
		t *testing.T,
		base *check.Absolute,
		c *pkg.Cache,
	) {
		destroyArtifact(t, base, c, a)
	}
}

// destroyStatus counts non-substitution status entries and destroys them.
func destroyStatus(t *testing.T, base *check.Absolute, c, s int) {
	dents, err := os.ReadDir(base.Append("status").String())
	if err != nil {
		t.Fatal(err)
	}

	var gotC, gotS int
	for _, dent := range dents {
		if err = os.Remove(base.Append(
			"status",
			dent.Name(),
		).String()); err != nil {
			t.Fatal(err)
		}

		if dent.Type().IsRegular() {
			gotC++
			continue
		}
		if dent.Type()&fs.ModeSymlink == fs.ModeSymlink {
			gotS++
			continue
		}
		t.Errorf("%s: %s", dent.Name(), dent.Type())
	}

	if gotC != c {
		t.Errorf("status: c = %d, want %d", gotC, c)
	}
	if gotS != s {
		t.Errorf("status: s = %d, want %d", gotS, s)
	}
}

func TestIdent(t *testing.T) {
	t.Parallel()

	testCases := []struct {
		name string
		a    pkg.Artifact
		want unique.Handle[pkg.ID]
	}{
		{"decompress", &stubArtifact{
			pkg.KindDecompress,
			[]byte{pkg.Gzip, 0, 0, 0, 0, 0, 0, 0},
			[]pkg.Artifact{
				overrideIdent{pkg.ID{}, new(stubArtifact)},
			},
			nil,
		}, unique.Make[pkg.ID](pkg.MustDecode(
			"fkmge-H56Ph2LzNNbEUjTypes8LfOxrF_CEXg07kq6ho_nbTNvzQde9-bjB7gyB_",
		))},
	}

	msg := message.New(log.New(os.Stderr, "ident: ", 0))
	msg.SwapVerbose(true)
	var cache *pkg.Cache
	if a, err := check.NewAbs(t.TempDir()); err != nil {
		t.Fatal(err)
	} else if cache, err = pkg.Open(t.Context(), msg, a, nil); err != nil {
		t.Fatal(err)
	}
	t.Cleanup(cache.Close)

	for _, tc := range testCases {
		t.Run(tc.name, func(t *testing.T) {
			t.Parallel()

			if got := cache.Ident(tc.a); got != tc.want {
				t.Errorf("Ident: %s, want %s",
					pkg.Encode(got.Value()),
					pkg.Encode(tc.want.Value()),
				)
			}
		})
	}
}

// An expectsKnown describes an expected file or directory.
type expectsKnown interface {
	// hash returns the checksum of the represented data.
	hash() (checksum pkg.Checksum)
}

// An expectsChecksum is a prepared checksum value.
type expectsChecksum pkg.Checksum

// hash returns e.
func (e expectsChecksum) hash() pkg.Checksum { return e }

// An expectsFile is the contents of a file expected by the test suite.
type expectsFile []byte

// hash computes the checksum of e.
func (e expectsFile) hash() (checksum pkg.Checksum) {
	h := sha512.New384()
	h.Write(e)
	h.Sum(checksum[:0])
	return
}

// An expectsFS describes the state of a filesystem expected by the test suite.
type expectsFS fstest.MapFS

// hash computes the checksum of e.
func (e expectsFS) hash() (checksum pkg.Checksum) {
	if err := pkg.SumFS(&checksum, fstest.MapFS(e), "."); err != nil {
		panic(err)
	}
	return
}

// expectsFrom generates expectsFS for a filesystem directory.
func expectsFrom(pathname string) string {
	var buf strings.Builder
	buf.WriteString("expectsFS{\n")
	if err := filepath.WalkDir(pathname, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}

		var rel string
		if rel, err = filepath.Rel(pathname, path); err != nil {
			return err
		}
		buf.WriteString("\t" + strconv.Quote(rel) + ": {Mode: ")

		var fi fs.FileInfo
		if fi, err = d.Info(); err != nil {
			return err
		}
		mode := fi.Mode()

		switch {
		case mode.IsDir():
			buf.WriteString("fs.ModeDir | 0" +
				strconv.FormatInt(int64(mode&^fs.ModeDir), 8))

		case mode&fs.ModeSymlink != 0:
			buf.WriteString("fs.ModeSymlink | 0" +
				strconv.FormatInt(int64(mode&^fs.ModeSymlink), 8) +
				", Data: []byte(")
			var linkname string
			if linkname, err = os.Readlink(path); err != nil {
				return err
			}
			buf.WriteString(strconv.Quote(linkname))
			buf.WriteByte(')')

		case mode.IsRegular():
			buf.WriteString("0" + strconv.FormatInt(int64(mode), 8))
			var p []byte
			if p, err = os.ReadFile(path); err != nil {
				return err
			}

			if len(p) > 0 {
				buf.WriteString(", Data: []byte(")
				buf.WriteString(strconv.Quote(unsafe.String(unsafe.SliceData(p), len(p))))
				buf.WriteByte(')')
			}
		}
		buf.WriteString("},\n")
		return nil
	}); err != nil {
		panic(err)
	}
	buf.WriteString("}")
	return buf.String()
}

// cacheTestCase is a test case passed to checkWithCache where a new instance
// of [pkg.Cache] is prepared for the test case, and is validated and removed
// on test completion.
type cacheTestCase struct {
	name  string
	flags int
	early func(t *testing.T, base *check.Absolute)
	f     func(t *testing.T, base *check.Absolute, c *pkg.Cache)
	want  expectsFS
}

const (
	// checkDestroySubstitutes arranges for substitutes to be destroyed before
	// measurement during checkWithCache.
	checkDestroySubstitutes = 1 << (iota + 32)
)

// makeBase returns a [pkg.Cache] base directory created for tb.
func makeBase(tb testing.TB) (base *check.Absolute) {
	tb.Helper()

	base = check.MustAbs(tb.TempDir())
	if err := os.Chmod(base.String(), 0700); err != nil {
		tb.Fatal(err)
	}
	tb.Cleanup(func() {
		if err := filepath.WalkDir(base.String(), func(path string, d fs.DirEntry, err error) error {
			if err != nil {
				tb.Error(err)
				return nil
			}
			if !d.IsDir() {
				return nil
			}
			return os.Chmod(path, 0700)
		}); err != nil {
			tb.Fatal(err)
		}
	})
	return
}

// checkWithCache runs a slice of cacheTestCase.
func checkWithCache(t *testing.T, testCases []cacheTestCase) {
	t.Helper()

	for _, tc := range testCases {
		t.Run(tc.name, func(t *testing.T) {
			t.Helper()
			t.Parallel()

			base := makeBase(t)
			msg := message.New(log.New(os.Stderr, "cache: ", 0))
			msg.SwapVerbose(testing.Verbose())

			flags := tc.flags | pkg.CSuppressInit

			if info.CanDegrade {
				if _, err := landlock.GetABI(); err != nil {
					if !errors.Is(err, syscall.ENOSYS) {
						t.Fatalf("LandlockGetABI: error = %v", err)
					}
					flags |= pkg.CHostAbstract
					t.Log("Landlock LSM is unavailable, setting CHostAbstract")
				}
			}

			var scrubFunc func() error // scrub after hashing
			if c, err := pkg.Open(t.Context(), msg, base, &pkg.CacheAttr{
				Cures: 1 << 4,
				Flags: flags,
			}); err != nil {
				t.Fatalf("Open: error = %v", err)
			} else {
				t.Cleanup(c.Close)
				if tc.early != nil {
					tc.early(t, base)
				}
				tc.f(t, base, c)
				scrubFunc = func() error {
					err = c.Scrub(1 << 7)
					idents, checksums, cleanErr := c.Clean(false, false)
					if len(idents) > 0 {
						t.Errorf("destroyed %d idents", len(idents))
					}
					if len(checksums) > 0 {
						t.Errorf("destroyed %d checksums", len(checksums))
					}
					return errors.Join(err, cleanErr)
				}
			}

			var restoreTemp bool
			if _, err := os.Lstat(base.Append("temp").String()); err != nil {
				if !errors.Is(err, os.ErrNotExist) {
					t.Fatal(err)
				}
			} else {
				restoreTemp = true
			}

			// destroy lock and variant file to avoid changing cache checksums
			for _, s := range []string{
				"lock",
				"variant",
			} {
				pathname := base.Append(s)
				if p, err := os.ReadFile(pathname.String()); err != nil {
					t.Fatal(err)
				} else if len(p) != 0 {
					t.Fatalf("file %q: %q", s, string(p))
				}
				if err := os.Remove(pathname.String()); err != nil {
					t.Fatal(err)
				}
			}

			// destroy non-deterministic substitutes
			if tc.flags&checkDestroySubstitutes != 0 {
				substitute := base.Append("substitute")
				if err := os.RemoveAll(substitute.String()); err != nil {
					t.Fatal(err)
				} else if err = os.Mkdir(substitute.String(), 0700); err != nil {
					t.Fatal(err)
				}
			}

			// destroy empty status directory
			if err := syscall.Rmdir(base.Append("status").String()); err != nil {
				if !errors.Is(err, syscall.ENOTEMPTY) {
					t.Fatal(err)
				}
			}

			// destroy empty fault directory
			if err := os.Remove(base.Append("fault").String()); err != nil {
				t.Fatal(err)
			}

			want := tc.want.hash()

			var checksum pkg.Checksum
			if err := pkg.SumDir(&checksum, base); err != nil {
				t.Fatalf("SumDir: error = %v", err)
			} else if checksum != want {
				t.Fatal(expectsFrom(base.String()))
			}

			if err := scrubFunc(); err != nil {
				t.Fatal("cache contains inconsistencies\n\n" + err.Error())
			}

			if restoreTemp {
				if err := os.Mkdir(
					base.Append("temp").String(),
					0700,
				); err != nil {
					t.Fatal(err)
				}
			}

			// validate again to make sure scrub did not condemn anything
			if err := pkg.SumDir(&checksum, base); err != nil {
				t.Fatalf("SumDir: error = %v", err)
			} else if checksum != want {
				t.Fatalf("(scrubbed) %s", expectsFrom(base.String()))
			}
		})
	}
}

// A cureStep contains an [Artifact] to be cured, and the expected outcome.
type cureStep struct {
	name string

	a pkg.Artifact

	pathname *check.Absolute
	output   expectsKnown
	whence   int
	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) {
	t.Helper()

	makeChecksumH := func(checksum pkg.Checksum) unique.Handle[pkg.Checksum] {
		if checksum == (pkg.Checksum{}) {
			return unique.Handle[pkg.Checksum]{}
		}
		return unique.Make(checksum)
	}

	for _, step := range steps {
		t.Log("cure step:", step.name)
		if pathname, checksum, whence, err := c.CureWhence(step.a); !reflect.DeepEqual(err, step.err) {
			faults, _err := c.ReadFaults(step.a)
			if _err != nil {
				t.Errorf("ReadFaults: error = %v", _err)
			}

			var p []byte
			for _, fault := range faults {
				p, _err = os.ReadFile(fault.String())
				if _err != nil {
					t.Error(_err)
					continue
				}
				t.Log(string(p))
				t.Logf("faulting cure terminated %s ago", time.Since(faults[0].Time()))
			}
			t.Fatalf("Cure: error = %v, want %v", err, step.err)
		} else if step.whence != whence {
			t.Fatalf("Cure: whence = %s, want %s", pkg.WhenceString(whence), pkg.WhenceString(step.whence))
		} else if step.pathname != ignorePathname && !pathname.Is(step.pathname) {
			t.Fatalf("Cure: pathname = %q, want %q", pathname, step.pathname)
		} else if step.output == nil || checksum != makeChecksumH(step.output.hash()) {
			if pathname != nil {
				if name, _err := filepath.EvalSymlinks(pathname.String()); _err != nil {
					t.Fatal(_err)
				} else {
					t.Fatal(expectsFrom(name))
				}
			} else if checksum != (unique.Handle[pkg.Checksum]{}) {
				t.Fatalf("Cure: unexpected checksum %s", pkg.Encode(checksum.Value()))
			}
		} else {
			v := any(err)
			if err == nil {
				v = pathname
			}
			var checksumVal pkg.Checksum
			if checksum != (unique.Handle[pkg.Checksum]{}) {
				checksumVal = checksum.Value()
			}
			t.Log(pkg.Encode(checksumVal)+":", v)
		}
	}
}

// newWantScrubError returns the address to a new [ScrubError] for base.
func newWantScrubError(base *check.Absolute) *pkg.ScrubError {
	return &pkg.ScrubError{
		ChecksumMismatches: []pkg.ChecksumMismatchError{
			{Got: pkg.MustDecode(
				"vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX",
			), Want: pkg.Checksum{0xff, 0}},
		},
		DanglingIdentifiers: []pkg.ID{
			{0xfe, 0},
			{0xfe, 0xfe},
			{0xfe, 0xff},
		},
		Errs: map[unique.Handle[string]][]error{
			base.Append("checksum", "__8AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA").Handle(): {
				pkg.InvalidFileModeError(fs.ModeSymlink),
			},

			base.Append("checksum", "invalid").Handle(): {
				base64.CorruptInputError(4),
			},

			base.Append("nonexistent").Handle(): {
				base64.CorruptInputError(8),
			},

			base.Append("identifier", pkg.Encode(pkg.ID{0xfe, 0xff})).Handle(): {
				&os.PathError{
					Op: "readlink",
					Path: base.Append(
						"identifier",
						pkg.Encode(pkg.ID{0xfe, 0xff}),
					).String(),
					Err: syscall.EINVAL,
				},
			},
			base.Append("identifier", "invalid").Handle(): {
				base64.CorruptInputError(4),
			},
		},
	}
}

func TestCache(t *testing.T) {
	t.Parallel()

	testdata := expectsFile("" +
		"\x00\x00\x00\x00" +
		"\xad\x0b\x00" +
		"\x04" +
		"\xfe\xfe\x00\x00" +
		"\xfe\xca\x00\x00")

	testCases := []cacheTestCase{
		{"file", pkg.CValidateKnown | pkg.CAssumeChecksum, nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
			identifier := (pkg.ID)(bytes.Repeat([]byte{
				0x75, 0xe6, 0x9d, 0x6d, 0xe7, 0x9f,
			}, 8))
			wantPathname := base.Append(
				"identifier",
				"deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef",
			)
			identifier0 := (pkg.ID)(bytes.Repeat([]byte{
				0x71, 0xa7, 0xde, 0x6d, 0xa6, 0xde,
			}, 8))
			wantPathname0 := base.Append(
				"identifier",
				"cafebabecafebabecafebabecafebabecafebabecafebabecafebabecafebabe",
			)
			failingFile := newStubFile(
				pkg.KindHTTPGet,
				pkg.ID{0xff, 3},
				nil,
				nil, struct {
					_ []byte
					stub.UniqueError
				}{UniqueError: 0xbad},
			)

			cureMany(t, c, []cureStep{
				{"initial file", newStubFile(
					pkg.KindHTTPGet,
					identifier,
					new(testdata.hash()),
					testdata, nil,
				), wantPathname, testdata, pkg.WNew, nil},

				{"identical content", newStubFile(
					pkg.KindHTTPGet,
					identifier0,
					new(testdata.hash()),
					testdata, nil,
				), wantPathname0, testdata, pkg.WCache, nil},

				{"existing entry", newStubFile(
					pkg.KindHTTPGet,
					identifier,
					new(testdata.hash()),
					testdata, nil,
				), wantPathname, testdata, pkg.WCache, nil},

				{"checksum mismatch", newStubFile(
					pkg.KindHTTPGet,
					pkg.ID{0xff, 0},
					new(pkg.Checksum),
					testdata, nil,
				), nil, nil, pkg.WNew, &pkg.ChecksumMismatchError{
					Got: testdata.hash(),
				}},

				{"store without validation", newStubFile(
					pkg.KindHTTPGet,
					pkg.MustDecode("vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX"),
					nil,
					[]byte{0}, nil,
				), base.Append(
					"identifier",
					"vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX",
				), expectsChecksum{
					0xbe, 0xc0, 0x21, 0xb4, 0xf3, 0x68,
					0xe3, 0x06, 0x91, 0x34, 0xe0, 0x12,
					0xc2, 0xb4, 0x30, 0x70, 0x83, 0xd3,
					0xa9, 0xbd, 0xd2, 0x06, 0xe2, 0x4e,
					0x5f, 0x0d, 0x86, 0xe1, 0x3d, 0x66,
					0x36, 0x65, 0x59, 0x33, 0xec, 0x2b,
					0x41, 0x34, 0x65, 0x96, 0x68, 0x17,
					0xa9, 0xc2, 0x08, 0xa1, 0x17, 0x17,
				}, pkg.WNew, nil},

				{"incomplete implementation", struct{ pkg.Artifact }{&stubArtifact{
					kind:   pkg.KindExec,
					params: []byte("artifact overridden to be incomplete"),
				}}, nil, nil, pkg.WNew, pkg.InvalidArtifactError(pkg.MustDecode(
					"poVrv3zNINbHd-WUJihwgWQwJpbHURFHfpY7Zux-ztto_bQhhS5PdpbNMjdkXv-V",
				))},

				{"error passthrough", newStubFile(
					pkg.KindHTTPGet,
					pkg.ID{0xff, 1},
					nil,
					nil, stub.UniqueError(0xcafe),
				), nil, nil, pkg.WNew, stub.UniqueError(0xcafe)},

				{"error caching", newStubFile(
					pkg.KindHTTPGet,
					pkg.ID{0xff, 1},
					nil,
					nil, nil,
				), nil, nil, pkg.WCache, stub.UniqueError(0xcafe)},

				{"cache hit bad type", overrideChecksum{testdata.hash(), overrideIdent{pkg.ID{0xff, 2}, &stubArtifact{
					kind: pkg.KindTar,
				}}}, nil, nil, pkg.WCache, pkg.InvalidFileModeError(
					0400,
				)},

				{"noncomparable error", &stubArtifactF{
					kind:   pkg.KindExec,
					params: []byte("artifact with dependency returning noncomparable error"),
					deps:   []pkg.Artifact{failingFile},

					cure: func(f *pkg.FContext) error {
						panic("attempting to cure impossible artifact")
					},
				}, nil, nil, pkg.WNew, &pkg.DependencyCureError{
					{
						A: failingFile,
						Err: struct {
							_ []byte
							stub.UniqueError
						}{UniqueError: 0xbad},
					},
				}},
			})

			if c0, err := pkg.Open(
				t.Context(),
				message.New(nil),
				base, &skipLock,
			); err != nil {
				t.Fatalf("open: error = %v", err)
			} else {
				t.Cleanup(c.Close) // check doubled cancel
				cureMany(t, c0, []cureStep{
					{"cache hit ident", overrideIdent{
						id: identifier,
					}, wantPathname, testdata, pkg.WCache, nil},

					{"cache miss checksum match", newStubFile(
						pkg.KindHTTPGet,
						testdata.hash(),
						nil,
						testdata,
						nil,
					), base.Append(
						"identifier",
						pkg.Encode(testdata.hash()),
					), testdata, pkg.WNew, nil},
				})

				// cure after close
				c.Close()
				if _, _, err = c.Cure(&stubArtifactF{
					kind:   pkg.KindExec,
					params: []byte("unreachable artifact cured after cancel"),
					deps:   []pkg.Artifact{pkg.NewFile("", []byte("unreachable dependency"))},
				}); !reflect.DeepEqual(err, context.Canceled) {
					t.Fatalf("(closed) Cure: error = %v", err)
				}
			}
		}, expectsFS{
			".": {Mode: fs.ModeDir | 0700},

			"checksum": {Mode: fs.ModeDir | 0700},
			"checksum/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX": {Mode: 0400, Data: []byte{0}},
			"checksum/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq": {Mode: 0400, Data: []byte{0, 0, 0, 0, 0xad, 0xb, 0, 4, 0xfe, 0xfe, 0, 0, 0xfe, 0xca, 0, 0}},

			"identifier": {Mode: fs.ModeDir | 0700},
			"identifier/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX")},
			"identifier/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq")},
			"identifier/cafebabecafebabecafebabecafebabecafebabecafebabecafebabecafebabe": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq")},
			"identifier/deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq")},

			"substitute": {Mode: fs.ModeDir | 0700},

			"work": {Mode: fs.ModeDir | 0700},
		}},

		{"directory", pkg.CAssumeChecksum, nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
			id := pkg.MustDecode(
				"HnySzeLQvSBZuTUcvfmLEX_OmH4yJWWH788NxuLuv7kVn8_uPM6Ks4rqFWM2NZJY",
			)
			makeSample := func(t *pkg.TContext) error {
				work := t.GetWorkDir()
				if err := os.Mkdir(work.String(), 0700); err != nil {
					return err
				}

				if err := os.WriteFile(
					work.Append("check").String(),
					[]byte{0, 0},
					0400,
				); err != nil {
					return err
				}

				if err := os.MkdirAll(work.Append(
					"lib",
					"pkgconfig",
				).String(), 0700); err != nil {
					return err
				}

				return os.Symlink(
					"/proc/nonexistent/libedac.so",
					work.Append(
						"lib",
						"libedac.so",
					).String(),
				)
			}
			want := expectsFS{
				".": {Mode: fs.ModeDir | 0500},

				"check": {Mode: 0400, Data: []byte{0, 0}},

				"lib":            {Mode: fs.ModeDir | 0700},
				"lib/libedac.so": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent/libedac.so")},

				"lib/pkgconfig": {Mode: fs.ModeDir | 0700},
			}
			wantPathname := base.Append(
				"identifier",
				pkg.Encode(id),
			)

			id0 := pkg.MustDecode(
				"Zx5ZG9BAwegNT3zQwCySuI2ktCXxNgxirkGLFjW4FW06PtojYVaCdtEw8yuntPLa",
			)
			wantPathname0 := base.Append(
				"identifier",
				pkg.Encode(id0),
			)

			makeGarbage := func(work *check.Absolute, wantErr error) error {
				if err := os.Mkdir(work.String(), 0700); err != nil {
					return err
				}

				mode := fs.FileMode(0)
				if wantErr == nil {
					mode = 0500
				}

				if err := os.MkdirAll(work.Append(
					"lib",
					"pkgconfig",
				).String(), 0700); err != nil {
					return err
				}

				if err := os.WriteFile(work.Append(
					"lib",
					"check",
				).String(), nil, 0400&mode); err != nil {
					return err
				}

				if err := os.Chmod(work.Append(
					"lib",
					"pkgconfig",
				).String(), 0500&mode); err != nil {
					return err
				}
				if err := os.Chmod(work.Append(
					"lib",
				).String(), 0500&mode); err != nil {
					return err
				}

				return wantErr
			}

			cureMany(t, c, []cureStep{
				{"initial directory", overrideChecksum{want.hash(), overrideIdent{id, &stubArtifact{
					kind: pkg.KindTar,
					cure: makeSample,
				}}}, wantPathname, want, pkg.WNew, nil},

				{"identical identifier", overrideChecksum{want.hash(), overrideIdent{id, &stubArtifact{
					kind: pkg.KindTar,
				}}}, wantPathname, want, pkg.WCache, nil},

				{"identical checksum", overrideIdent{id0, &stubArtifact{
					kind: pkg.KindTar,
					cure: makeSample,
				}}, wantPathname0, want, pkg.WNew, nil},

				{"cure fault", overrideIdent{pkg.ID{0xff, 0}, &stubArtifact{
					kind: pkg.KindTar,
					cure: func(t *pkg.TContext) error {
						return makeGarbage(t.GetWorkDir(), stub.UniqueError(0xcafe))
					},
				}}, nil, nil, pkg.WNew, stub.UniqueError(0xcafe)},

				{"checksum mismatch", overrideChecksum{pkg.Checksum{}, overrideIdent{pkg.ID{0xff, 1}, &stubArtifact{
					kind: pkg.KindTar,
					cure: func(t *pkg.TContext) error {
						return makeGarbage(t.GetWorkDir(), nil)
					},
				}}}, nil, nil, pkg.WNew, &pkg.ChecksumMismatchError{
					Got: pkg.MustDecode(
						"CUx-3hSbTWPsbMfDhgalG4Ni_GmR9TnVX8F99tY_P5GtkYvczg9RrF5zO0jX9XYT",
					),
				}},

				{"cache hit bad type", newStubFile(
					pkg.KindHTTPGet,
					pkg.ID{0xff, 2},
					new(want.hash()),
					testdata, nil,
				), nil, nil, pkg.WCache, pkg.InvalidFileModeError(
					fs.ModeDir | 0500,
				)},

				{"openFile directory", overrideIdent{pkg.ID{0xff, 3}, &stubArtifact{
					kind: pkg.KindTar,
					cure: func(t *pkg.TContext) error {
						r, err := t.Open(overrideChecksumFile{checksum: want.hash()})
						if err != nil {
							panic(err)
						}
						_, err = io.ReadAll(r)
						return err
					},
				}}, nil, nil, pkg.WNew, &os.PathError{
					Op: "read",
					Path: base.Append(
						"checksum",
						pkg.Encode(want.hash()),
					).String(),
					Err: syscall.EISDIR,
				}},

				{"no output", overrideIdent{pkg.ID{0xff, 4}, &stubArtifact{
					kind: pkg.KindTar,
					cure: func(t *pkg.TContext) error {
						return nil
					},
				}}, nil, nil, pkg.WNew, pkg.NoOutputError{}},

				{"file output", overrideIdent{pkg.ID{0xff, 5}, &stubArtifact{
					kind: pkg.KindTar,
					cure: func(t *pkg.TContext) error {
						return os.WriteFile(t.GetWorkDir().String(), []byte{0}, 0400)
					},
				}}, nil, nil, pkg.WNew, errors.New("non-file artifact produced regular file")},

				{"symlink output", overrideIdent{pkg.ID{0xff, 6}, &stubArtifact{
					kind: pkg.KindTar,
					cure: func(t *pkg.TContext) error {
						return os.Symlink(
							t.GetWorkDir().String(),
							t.GetWorkDir().String(),
						)
					},
				}}, nil, nil, pkg.WNew, pkg.InvalidFileModeError(
					fs.ModeSymlink | 0777,
				)},

				{"alternative", &stubArtifactF{
					kind:   pkg.KindExec,
					params: []byte("substitutable artifact"),
					deps: []pkg.Artifact{newStubFile(
						pkg.KindHTTPGet,
						pkg.ID{0xff, 8},
						nil,
						[]byte("substitutable dependency"),
						nil,
					)},

					cure: func(f *pkg.FContext) error {
						return makeSample(&f.TContext)
					},
				}, base.Append(
					"identifier",
					"gIH5eti07nBAhVti3ZTn8EIGOBCZWWvNpxg5CmCZlDzIC4mBdomPmQLeEpf1IQg9",
				), want, pkg.WNew, nil},

				{"substitutable", &stubArtifactF{
					kind:   pkg.KindExec,
					params: []byte("substitutable artifact"),
					deps: []pkg.Artifact{newStubFile(
						pkg.KindHTTPGet,
						pkg.ID{0xff, 10},
						nil,
						[]byte("substitutable dependency"),
						nil,
					)},

					cure: func(f *pkg.FContext) error {
						panic("substitution missed")
					},
				}, base.Append(
					"identifier",
					"VGjpp7NVw3OYLpgOQumfM0KcJgY3suz6torykUczcg4bGT24ySkPn5hy-4dNqqkR",
				), want, pkg.WSubstitute, nil},
			})

			if c0, err := pkg.Open(
				t.Context(),
				message.New(nil),
				base, &skipLock,
			); err != nil {
				t.Fatalf("open: error = %v", err)
			} else {
				t.Cleanup(c.Close)
				cureMany(t, c0, []cureStep{
					{"substitutable", &stubArtifactF{
						kind:   pkg.KindExec,
						params: []byte("substitutable artifact"),
						deps: []pkg.Artifact{newStubFile(
							pkg.KindHTTPGet,
							pkg.ID{0xff, 0xff, 0xfd, 0xfd},
							nil,
							[]byte("substitutable dependency"),
							nil,
						)},

						cure: func(f *pkg.FContext) error {
							panic("substitution missed")
						},
					}, base.Append(
						"identifier",
						"zeZ4JEZ0atAKl6Am67cBID6-KR18nZGgeYfU4qTuYaWhQC4eAn0dyTXdIBH9Bos8",
					), want, pkg.WSubstitute, nil},
				})
			}

			if dents, err := os.ReadDir(base.Append("status").String()); err != nil {
				t.Fatal(err)
			} else if len(dents) > 0 {
				t.Errorf("ReadDir: %v", dents)
			}

		}, expectsFS{
			".": {Mode: fs.ModeDir | 0700},

			"checksum": {Mode: fs.ModeDir | 0700},
			"checksum/7lfQ4QwSpV8nw7IDh0JiQ_jqUPrPv3_Vfie034RxsSy-cy4vO8DVvxgpx2LW08oO":                {Mode: 0400, Data: []byte("substitutable dependency")},
			"checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b":                {Mode: fs.ModeDir | 0500},
			"checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b/check":          {Mode: 0400, Data: []byte{0, 0}},
			"checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b/lib":            {Mode: fs.ModeDir | 0700},
			"checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b/lib/pkgconfig":  {Mode: fs.ModeDir | 0700},
			"checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b/lib/libedac.so": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent/libedac.so")},

			"identifier": {Mode: fs.ModeDir | 0700},
			"identifier/HnySzeLQvSBZuTUcvfmLEX_OmH4yJWWH788NxuLuv7kVn8_uPM6Ks4rqFWM2NZJY": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b")},
			"identifier/Zx5ZG9BAwegNT3zQwCySuI2ktCXxNgxirkGLFjW4FW06PtojYVaCdtEw8yuntPLa": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b")},
			"identifier/zeZ4JEZ0atAKl6Am67cBID6-KR18nZGgeYfU4qTuYaWhQC4eAn0dyTXdIBH9Bos8": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b")},
			"identifier/___9_QAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/7lfQ4QwSpV8nw7IDh0JiQ_jqUPrPv3_Vfie034RxsSy-cy4vO8DVvxgpx2LW08oO")},
			"identifier/_wgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/7lfQ4QwSpV8nw7IDh0JiQ_jqUPrPv3_Vfie034RxsSy-cy4vO8DVvxgpx2LW08oO")},
			"identifier/_woAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/7lfQ4QwSpV8nw7IDh0JiQ_jqUPrPv3_Vfie034RxsSy-cy4vO8DVvxgpx2LW08oO")},
			"identifier/VGjpp7NVw3OYLpgOQumfM0KcJgY3suz6torykUczcg4bGT24ySkPn5hy-4dNqqkR": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b")},
			"identifier/gIH5eti07nBAhVti3ZTn8EIGOBCZWWvNpxg5CmCZlDzIC4mBdomPmQLeEpf1IQg9": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b")},

			"substitute": {Mode: fs.ModeDir | 0700},
			"substitute/nWPg893oqn_YNN8kgfZrs_LVLwP90e0mKxqU8UwoazQh-yBPwhoviD7of6YALx-M": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b")},

			"work": {Mode: fs.ModeDir | 0700},
		}},

		{"pending", pkg.CValidateKnown, nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
			wantErr := stub.UniqueError(0xcafe)
			n, ready := make(chan struct{}), make(chan struct{})
			go func() {
				if _, _, err := c.Cure(overrideIdent{pkg.ID{0xff}, &stubArtifact{
					kind: pkg.KindTar,
					cure: func(t *pkg.TContext) error {
						close(ready)
						<-n
						return wantErr
					},
				}}); !reflect.DeepEqual(err, wantErr) {
					panic(fmt.Sprintf("Cure: error = %v, want %v", err, wantErr))
				}
			}()

			<-ready
			wCureDone := make(chan struct{})
			go func() {
				if _, _, err := c.Cure(overrideIdent{pkg.ID{0xff}, &stubArtifact{
					kind: pkg.KindTar,
				}}); !reflect.DeepEqual(err, wantErr) {
					panic(fmt.Sprintf("Cure: error = %v, want %v", err, wantErr))
				}
				close(wCureDone)
			}()

			// check cache activity while a cure is blocking
			cureMany(t, c, []cureStep{
				{"error passthrough", newStubFile(
					pkg.KindHTTPGet,
					pkg.ID{0xff, 1},
					nil,
					nil, stub.UniqueError(0xbad),
				), nil, nil, pkg.WNew, stub.UniqueError(0xbad)},

				{"file output", overrideIdent{pkg.ID{0xff, 2}, &stubArtifact{
					kind: pkg.KindTar,
					cure: func(t *pkg.TContext) error {
						return os.WriteFile(
							t.GetWorkDir().String(),
							[]byte{0},
							0400,
						)
					},
				}}, nil, nil, pkg.WNew, errors.New(
					"non-file artifact produced regular file",
				)},
			})

			wantErrScrub := &pkg.ScrubError{
				Errs: map[unique.Handle[string]][]error{
					base.Handle(): {errors.New("scrub began with pending artifacts")},
				},
			}
			if err := c.Scrub(1 << 6); !reflect.DeepEqual(err, wantErrScrub) {
				t.Fatalf("Scrub: error = %#v, want %#v", err, wantErrScrub)
			}

			notify := c.Done(unique.Make(pkg.ID{0xff}))
			go close(n)
			if notify != nil {
				<-notify
			}
			for c.Done(unique.Make(pkg.ID{0xff})) != nil {
			}
			<-wCureDone
		}, expectsFS{
			".":          {Mode: fs.ModeDir | 0700},
			"checksum":   {Mode: fs.ModeDir | 0700},
			"identifier": {Mode: fs.ModeDir | 0700},
			"substitute": {Mode: fs.ModeDir | 0700},
			"work":       {Mode: fs.ModeDir | 0700},
		}},

		{"cancel abort block", pkg.CValidateKnown, nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
			var wg sync.WaitGroup
			defer wg.Wait()

			var started sync.WaitGroup
			defer started.Wait()

			blockCures := func(d byte, e stub.UniqueError, n int) {
				started.Add(n)
				for i := range n {
					wg.Go(func() {
						if _, _, err := c.Cure(overrideIdent{pkg.ID{d, byte(i)}, &stubArtifact{
							kind: pkg.KindTar,
							cure: func(t *pkg.TContext) error {
								started.Done()
								<-t.Unwrap().Done()
								return e + stub.UniqueError(i)
							},
						}}); !reflect.DeepEqual(err, e+stub.UniqueError(i)) {
							panic(err)
						}
					})
				}
				started.Wait()
			}

			blockCures(0xfd, 0xbad, 16)
			c.Abort()
			wg.Wait()

			blockCures(0xfd, 0xcafe, 16)
			c.Abort()
			wg.Wait()

			blockCures(0xff, 0xbad, 1)
			if !c.Cancel(unique.Make(pkg.ID{0xff})) {
				t.Fatal("missed cancellation")
			}
			wg.Wait()

			blockCures(0xff, 0xcafe, 1)
			if !c.Cancel(unique.Make(pkg.ID{0xff})) {
				t.Fatal("missed cancellation")
			}
			wg.Wait()

			for c.Cancel(unique.Make(pkg.ID{0xff})) {
			}

			c.Close()
			c.Abort()
		}, expectsFS{
			".":          {Mode: fs.ModeDir | 0700},
			"checksum":   {Mode: fs.ModeDir | 0700},
			"identifier": {Mode: fs.ModeDir | 0700},
			"substitute": {Mode: fs.ModeDir | 0700},
			"work":       {Mode: fs.ModeDir | 0700},
		}},

		{"no assume checksum", 0, nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
			makeGarbage := func(work *check.Absolute, wantErr error) error {
				if err := os.Mkdir(work.String(), 0700); err != nil {
					return err
				}

				if err := os.WriteFile(work.Append(
					"check",
				).String(), nil, 0400); err != nil {
					return err
				}

				return wantErr
			}

			want := expectsChecksum(pkg.MustDecode(
				"Aubi5EG4_Y8DhL9bQ3Q4HFBhLRF7X5gt9D3CNCQfT-TeBtlRXc7Zi_JYZEMoCC7M",
			))

			cureMany(t, c, []cureStep{
				{"create", overrideChecksum{want.hash(), overrideIdent{pkg.ID{0xff, 0}, &stubArtifact{
					kind: pkg.KindTar,
					cure: func(t *pkg.TContext) error {
						return makeGarbage(t.GetWorkDir(), nil)
					},
				}}}, base.Append(
					"identifier",
					pkg.Encode(pkg.ID{0xff, 0}),
				), want, pkg.WNew, nil},

				{"reject", overrideChecksum{want.hash(), overrideIdent{pkg.ID{0xfe, 1}, &stubArtifact{
					kind: pkg.KindTar,
					cure: func(t *pkg.TContext) error {
						return makeGarbage(t.GetWorkDir(), stub.UniqueError(0xbad))
					},
				}}}, nil, nil, pkg.WNew, stub.UniqueError(0xbad)},

				{"match", overrideChecksum{want.hash(), overrideIdent{pkg.ID{0xff, 1}, &stubArtifact{
					kind: pkg.KindTar,
					cure: func(t *pkg.TContext) error {
						return makeGarbage(t.GetWorkDir(), nil)
					},
				}}}, base.Append(
					"identifier",
					pkg.Encode(pkg.ID{0xff, 1}),
				), want, pkg.WNew, nil},
			})
		}, expectsFS{
			".": {Mode: fs.ModeDir | 0700},

			"checksum": {Mode: fs.ModeDir | 0700},
			"checksum/Aubi5EG4_Y8DhL9bQ3Q4HFBhLRF7X5gt9D3CNCQfT-TeBtlRXc7Zi_JYZEMoCC7M":       {Mode: fs.ModeDir | 0500},
			"checksum/Aubi5EG4_Y8DhL9bQ3Q4HFBhLRF7X5gt9D3CNCQfT-TeBtlRXc7Zi_JYZEMoCC7M/check": {Mode: 0400, Data: []byte{}},

			"identifier": {Mode: fs.ModeDir | 0700},
			"identifier/_wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/Aubi5EG4_Y8DhL9bQ3Q4HFBhLRF7X5gt9D3CNCQfT-TeBtlRXc7Zi_JYZEMoCC7M")},
			"identifier/_wEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/Aubi5EG4_Y8DhL9bQ3Q4HFBhLRF7X5gt9D3CNCQfT-TeBtlRXc7Zi_JYZEMoCC7M")},

			"substitute": {Mode: fs.ModeDir | 0700},

			"work": {Mode: fs.ModeDir | 0700},
		}},

		{"scrub", 0, nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
			cureMany(t, c, []cureStep{
				{"bad measured file", newStubFile(
					pkg.KindHTTPGet,
					pkg.Checksum{0xfe, 0},
					&pkg.Checksum{0xff, 0},
					[]byte{0}, nil,
				), base.Append(
					"identifier",
					pkg.Encode(pkg.Checksum{0xfe, 0}),
				), expectsChecksum{0xff, 0}, pkg.WNew, nil},
			})

			for _, p := range [][]string{
				{"identifier", "invalid"},
				{"identifier", pkg.Encode(pkg.ID{0xfe, 0xff})},
				{"checksum", "invalid"},
			} {
				if err := os.WriteFile(
					base.Append(p...).String(),
					nil,
					0400,
				); err != nil {
					t.Fatal(err)
				}
			}

			for _, p := range [][]string{
				{"../nonexistent", "checksum", pkg.Encode(pkg.Checksum{0xff, 0xff})},
				{"../nonexistent", "identifier", pkg.Encode(pkg.Checksum{0xfe, 0xfe})},
			} {
				if err := os.Symlink(
					p[0],
					base.Append(p[1:]...).String(),
				); err != nil {
					t.Fatal(err)
				}
			}

			wantErr := newWantScrubError(base)
			if err := c.Scrub(1 << 6); !reflect.DeepEqual(err, wantErr) {
				t.Fatalf("Scrub: error =\n%s\nwant\n%s", err, wantErr)
			}
		}, expectsFS{
			".":          {Mode: fs.ModeDir | 0700},
			"checksum":   {Mode: fs.ModeDir | 0700},
			"identifier": {Mode: fs.ModeDir | 0700},
			"substitute": {Mode: fs.ModeDir | 0700},
			"work":       {Mode: fs.ModeDir | 0700},
		}},

		{"status substitute clean", 0, nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
			destroyed := &stubArtifactF{
				kind:   pkg.KindExec,
				params: []byte("destroyed"),
				deps: []pkg.Artifact{
					pkg.NewFile("destroyed-input", []byte("destroyed")),
				},
				cure: func(f *pkg.FContext) error {
					if w, err := f.GetStatusWriter(); err != nil {
						return err
					} else if _, err = w.Write([]byte("destroyed")); err != nil {
						return err
					}

					p := f.GetWorkDir()
					if err := os.MkdirAll(p.String(), 0755); err != nil {
						return err
					}
					return os.WriteFile(p.Append("result").String(), nil, 0444)
				},
			}
			substituted := new(*destroyed)
			substituted.deps = []pkg.Artifact{
				pkg.NewFile("destroyed-input-0", []byte("destroyed")),
			}
			substituted.cure = func(*pkg.FContext) error {
				panic("substitutable cure reached")
			}

			cureMany(t, c, []cureStep{
				{"destroyed", destroyed, base.Append(
					"identifier",
					pkg.Encode(c.Ident(destroyed).Value()),
				), expectsFS{
					".":      {Mode: fs.ModeDir | 0500},
					"result": {Mode: 0444},
				}, pkg.WNew, nil},

				{"substituted", substituted, base.Append(
					"identifier",
					pkg.Encode(c.Ident(substituted).Value()),
				), expectsFS{
					".":      {Mode: fs.ModeDir | 0500},
					"result": {Mode: 0444},
				}, pkg.WSubstitute, nil},
			})
		}, expectsFS{
			".": {Mode: fs.ModeDir | 0700},

			"checksum": {Mode: fs.ModeDir | 0700},
			"checksum/UjZSrgz7_B7XMd9fHU7jM33UZhWlFgX0rz7JZbCBYR28bCS7jr_CAJdcDhi52ruE":        {Mode: fs.ModeDir | 0500},
			"checksum/UjZSrgz7_B7XMd9fHU7jM33UZhWlFgX0rz7JZbCBYR28bCS7jr_CAJdcDhi52ruE/result": {Mode: 0444},
			"checksum/wILUy2izpj2sgKJVhGUGIAde1XVuqvp5BpFMIQHanT5Q8R6jK4QPVSrJsjZh-njV":        {Mode: 0400, Data: []byte("destroyed")},

			"identifier": {Mode: fs.ModeDir | 0700},
			"identifier/2vZYAE7AVme2W3EgcDP1QUfwrmgFWIswUQBd6ZIBtiCal-MLiCtAg940Jzed5w4_": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/UjZSrgz7_B7XMd9fHU7jM33UZhWlFgX0rz7JZbCBYR28bCS7jr_CAJdcDhi52ruE")},
			"identifier/42lkARs2-xl_7wXfjPB0DaOXH8U2BKimaDYX-POJv5l01ArTKMbABt_kUMp24F1U": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/wILUy2izpj2sgKJVhGUGIAde1XVuqvp5BpFMIQHanT5Q8R6jK4QPVSrJsjZh-njV")},
			"identifier/H5pfX9loHFLORmMrMFCDbVUGg0RtxUDj4GHs21Q6bD8PTiAaFVGLnTQlhbMC5Z0G": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/UjZSrgz7_B7XMd9fHU7jM33UZhWlFgX0rz7JZbCBYR28bCS7jr_CAJdcDhi52ruE")},
			"identifier/sZVN1nOxhdWvZnus3nPTe6q0SqqzObfNBsJNnVu6Co6ajKA9wCiUP33MOdaaEt7K": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/wILUy2izpj2sgKJVhGUGIAde1XVuqvp5BpFMIQHanT5Q8R6jK4QPVSrJsjZh-njV")},

			"status": {Mode: fs.ModeDir | 0700},
			"status/H5pfX9loHFLORmMrMFCDbVUGg0RtxUDj4GHs21Q6bD8PTiAaFVGLnTQlhbMC5Z0G": {Mode: fs.ModeSymlink | 0777, Data: []byte("dP-6_wIDRRouOaOF-nkBy-IaUbLdYHbOUTrptu7j_qfW01mnHSjYJ0oykUmvUd2x")},
			"status/2vZYAE7AVme2W3EgcDP1QUfwrmgFWIswUQBd6ZIBtiCal-MLiCtAg940Jzed5w4_": {Mode: 0400, Data: []byte(statusHeader + "destroyed")},
			"status/dP-6_wIDRRouOaOF-nkBy-IaUbLdYHbOUTrptu7j_qfW01mnHSjYJ0oykUmvUd2x": {Mode: 0400, Data: []byte(statusHeader + "destroyed")},

			"substitute": {Mode: fs.ModeDir | 0700},
			"substitute/dP-6_wIDRRouOaOF-nkBy-IaUbLdYHbOUTrptu7j_qfW01mnHSjYJ0oykUmvUd2x": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/UjZSrgz7_B7XMd9fHU7jM33UZhWlFgX0rz7JZbCBYR28bCS7jr_CAJdcDhi52ruE")},

			"work": {Mode: fs.ModeDir | 0700},
		}},

		{"extern", 0, nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
			a := &stubArtifactF{
				kind:   pkg.KindExec,
				params: []byte("extern"),
			}
			wantIdent := c.Ident(a)
			wantOutput := expectsFS{
				".":      {Mode: fs.ModeDir | 0500},
				"result": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent")},
			}
			var wantChecksum pkg.Checksum
			if err := pkg.SumFS(
				&wantChecksum,
				fstest.MapFS(wantOutput),
				".",
			); err != nil {
				t.Fatal(err)
			}
			wantChecksumH := unique.Make(wantChecksum)

			_a := &stubArtifactF{
				kind:   pkg.KindExec,
				params: []byte("extern substitute"),
				deps:   []pkg.Artifact{pkg.NewFile("", nil)},
			}
			_wantIdent := c.Ident(_a)
			_wantOutput := expectsFS{
				".": {Mode: fs.ModeDir | 0500},
			}
			var _wantChecksum pkg.Checksum
			if err := pkg.SumFS(
				&_wantChecksum,
				fstest.MapFS(_wantOutput),
				".",
			); err != nil {
				t.Fatal(err)
			}
			_wantChecksumH := unique.Make(_wantChecksum)

			kca := pkg.NewExec(
				"", "",
				new(pkg.Checksum), 0, false, false,
				fhs.AbsRoot, nil, fhs.AbsRoot, nil,
			)
			kcIdent := c.Ident(kca)

			c.SetExternal(stubExtern{
				artifact: map[unique.Handle[pkg.ID]]pkg.Checksum{
					wantIdent:  wantChecksum,
					_wantIdent: _wantChecksum,
					kcIdent:    wantChecksum,
				},
				checksum: map[unique.Handle[pkg.Checksum]]fstest.MapFS{
					wantChecksumH:  fstest.MapFS(wantOutput),
					_wantChecksumH: fstest.MapFS(_wantOutput),
				},
				status: map[unique.Handle[pkg.ID]]string{
					wantIdent: "\x00",
					kcIdent:   "unreachable",
				},
			})

			cureMany(t, c, []cureStep{
				{"extern", a, base.Append(
					"identifier",
					pkg.Encode(wantIdent.Value()),
				), wantOutput, pkg.WExternal, nil},

				{"substitute", _a, base.Append(
					"identifier",
					pkg.Encode(_wantIdent.Value()),
				), _wantOutput, pkg.WExternal, nil},

				{"mismatch", kca, nil, nil, pkg.WExternal, &pkg.ChecksumMismatchError{
					Got: wantChecksum,
				}},
			})
		}, expectsFS{
			".": {Mode: fs.ModeDir | 0700},

			"checksum": {Mode: fs.ModeDir | 0700},
			"checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU":        {Mode: fs.ModeDir | 0500},
			"checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb":        {Mode: 0400},
			"checksum/fHkl_RuHOoc4rso__nV-qreikovd6Yhrq5mpBlkf5hmPGaxDlik2bYOQ4dhUQjtl":        {Mode: fs.ModeDir | 0500},
			"checksum/fHkl_RuHOoc4rso__nV-qreikovd6Yhrq5mpBlkf5hmPGaxDlik2bYOQ4dhUQjtl/result": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent")},

			"identifier": {Mode: fs.ModeDir | 0700},
			"identifier/PITQy8S3pqQRTJOE9lPJVjUMri6jSuknElXX7SaUVtUTQqByg79dI-kpc6J2GNeY": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
			"identifier/TI4SrHTEYRZ9yeiJzPqPULx4pl1hVSFgZ7DTweQSwk49k8lAIC1A5UrPs45P3Hi6": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/fHkl_RuHOoc4rso__nV-qreikovd6Yhrq5mpBlkf5hmPGaxDlik2bYOQ4dhUQjtl")},
			"identifier/xCv2q_KJpNoTkXI9ua5UMAC1ndSrCeAhlQ9njUcwXCSd_qAnSXkgOy7uluHWWD3o": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
			"identifier/DyLrgassC_E06vPgPzQFuCOxwoccc08C04FSuI6aliWWXdJLWnJt9R9OXwoakhhm": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb")},
			"identifier/8VL-egZySw-RbnHZtxGWdf5Z2v9S9CihrdFwa54Bc5EYMQcEgWEem7QrdCTWlCb8": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/fHkl_RuHOoc4rso__nV-qreikovd6Yhrq5mpBlkf5hmPGaxDlik2bYOQ4dhUQjtl")},

			"status": {Mode: fs.ModeDir | 0700},
			"status/8VL-egZySw-RbnHZtxGWdf5Z2v9S9CihrdFwa54Bc5EYMQcEgWEem7QrdCTWlCb8": {Mode: 0400, Data: []byte("\x00")},

			"substitute": {Mode: fs.ModeDir | 0700},
			"substitute/socGRnhdsJlJ4Z01ZwHFZdLzFH0rWvoaJrylcUKtvhBdGsE7VoYl-vdUuvfK8B4I": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},

			"work": {Mode: fs.ModeDir | 0700},
		}},

		{"extern shallow", pkg.CExternShallow, nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
			a := &stubArtifactF{
				kind:   pkg.KindExec,
				params: []byte("extern"),
			}
			wantIdent := c.Ident(a)
			wantOutput := expectsFS{
				".":      {Mode: fs.ModeDir | 0500},
				"result": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent")},
			}
			var wantChecksum pkg.Checksum
			if err := pkg.SumFS(
				&wantChecksum,
				fstest.MapFS(wantOutput),
				".",
			); err != nil {
				t.Fatal(err)
			}
			wantChecksumH := unique.Make(wantChecksum)

			_a := &stubArtifactF{
				kind:   pkg.KindExec,
				params: []byte("extern substitute"),
				deps:   []pkg.Artifact{pkg.NewFile("", nil)},
			}
			_wantIdent := c.Ident(_a)
			_wantOutput := expectsFS{
				".": {Mode: fs.ModeDir | 0500},
			}
			var _wantChecksum pkg.Checksum
			if err := pkg.SumFS(
				&_wantChecksum,
				fstest.MapFS(_wantOutput),
				".",
			); err != nil {
				t.Fatal(err)
			}
			_wantChecksumH := unique.Make(_wantChecksum)

			kca := pkg.NewExec(
				"", "",
				new(pkg.Checksum), 0, false, false,
				fhs.AbsRoot, nil, fhs.AbsRoot, nil,
			)
			kcIdent := c.Ident(kca)

			fia := &stubArtifactF{
				kind:   pkg.KindExec,
				params: []byte("flood input"),
				deps:   []pkg.Artifact{_a},
			}
			fiaIdent := c.Ident(fia)

			flia := &stubArtifactF{
				kind:   pkg.KindExec,
				params: []byte("flood input local"),
				deps:   []pkg.Artifact{_a},
			}
			fliaIdent := c.Ident(flia)

			h := &stubArtifactF{
				kind:   pkg.KindExec,
				params: []byte("hanging input"),
			}

			fhia := &stubArtifactF{
				kind:   pkg.KindExec,
				params: []byte("flood input local"),
				deps:   []pkg.Artifact{h},
			}
			fhiaIdent := c.Ident(fhia)

			c.SetExternal(stubExtern{
				artifact: map[unique.Handle[pkg.ID]]pkg.Checksum{
					wantIdent:  wantChecksum,
					_wantIdent: _wantChecksum,
					kcIdent:    wantChecksum,
					fiaIdent:   wantChecksum,
					fliaIdent:  wantChecksum,
					fhiaIdent:  wantChecksum,
				},
				checksum: map[unique.Handle[pkg.Checksum]]fstest.MapFS{
					wantChecksumH:  fstest.MapFS(wantOutput),
					_wantChecksumH: fstest.MapFS(_wantOutput),
				},
				status: map[unique.Handle[pkg.ID]]string{
					wantIdent: "\x00",
					kcIdent:   "unreachable",
				},
			})

			cureMany(t, c, []cureStep{
				{"extern", a, base.Append(
					"identifier",
					pkg.Encode(wantIdent.Value()),
				), wantOutput, pkg.WExternal, nil},

				{"flood shallow extern", fia, base.Append(
					"identifier",
					pkg.Encode(fiaIdent.Value()),
				), wantOutput, pkg.WExternal, nil},

				{"substitute", _a, base.Append(
					"identifier",
					pkg.Encode(_wantIdent.Value()),
				), _wantOutput, pkg.WExternal, nil},

				{"flood shallow local", flia, base.Append(
					"identifier",
					pkg.Encode(fliaIdent.Value()),
				), wantOutput, pkg.WExternal, nil},

				{"flood shallow hanging", fhia, nil, nil,
					pkg.WNew, pkg.HangingInputError(c.Ident(h))},

				{"mismatch", kca, nil, nil, pkg.WExternal, &pkg.ChecksumMismatchError{
					Got: wantChecksum,
				}},
			})
		}, expectsFS{
			".": {Mode: fs.ModeDir | 0700},

			"checksum": {Mode: fs.ModeDir | 0700},
			"checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU":        {Mode: fs.ModeDir | 0500},
			"checksum/fHkl_RuHOoc4rso__nV-qreikovd6Yhrq5mpBlkf5hmPGaxDlik2bYOQ4dhUQjtl":        {Mode: fs.ModeDir | 0500},
			"checksum/fHkl_RuHOoc4rso__nV-qreikovd6Yhrq5mpBlkf5hmPGaxDlik2bYOQ4dhUQjtl/result": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent")},

			"identifier": {Mode: fs.ModeDir | 0700},
			"identifier/xCv2q_KJpNoTkXI9ua5UMAC1ndSrCeAhlQ9njUcwXCSd_qAnSXkgOy7uluHWWD3o": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
			"identifier/uaLFpraDJ8JOCFT94FhrVCNn9R2iXozSw3W4Rt_zdAKhlViF36CGjjwL6IJoe4fU": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/fHkl_RuHOoc4rso__nV-qreikovd6Yhrq5mpBlkf5hmPGaxDlik2bYOQ4dhUQjtl")},
			"identifier/aCVm-QVKHmWPyHu02CjnJ5xXlIr78nNQRv1x9HhFRamQkaYesdubZFy-m7JxI38v": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/fHkl_RuHOoc4rso__nV-qreikovd6Yhrq5mpBlkf5hmPGaxDlik2bYOQ4dhUQjtl")},
			"identifier/PITQy8S3pqQRTJOE9lPJVjUMri6jSuknElXX7SaUVtUTQqByg79dI-kpc6J2GNeY": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
			"identifier/8VL-egZySw-RbnHZtxGWdf5Z2v9S9CihrdFwa54Bc5EYMQcEgWEem7QrdCTWlCb8": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/fHkl_RuHOoc4rso__nV-qreikovd6Yhrq5mpBlkf5hmPGaxDlik2bYOQ4dhUQjtl")},
			"identifier/TI4SrHTEYRZ9yeiJzPqPULx4pl1hVSFgZ7DTweQSwk49k8lAIC1A5UrPs45P3Hi6": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/fHkl_RuHOoc4rso__nV-qreikovd6Yhrq5mpBlkf5hmPGaxDlik2bYOQ4dhUQjtl")},

			"status": {Mode: fs.ModeDir | 0700},
			"status/8VL-egZySw-RbnHZtxGWdf5Z2v9S9CihrdFwa54Bc5EYMQcEgWEem7QrdCTWlCb8": {Mode: 0400, Data: []byte("\x00")},

			"substitute": {Mode: fs.ModeDir | 0700},
			"substitute/socGRnhdsJlJ4Z01ZwHFZdLzFH0rWvoaJrylcUKtvhBdGsE7VoYl-vdUuvfK8B4I": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
			"substitute/MccYezQ4pshkeBV4w_aAEIwvZdKHL3OAgAkR3ouZ43EF94Ur1HBHaN7njPfJAj50": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/fHkl_RuHOoc4rso__nV-qreikovd6Yhrq5mpBlkf5hmPGaxDlik2bYOQ4dhUQjtl")},
			"substitute/VV5W0_DiA1iylaqbKFThp1ZpV_y1ccVS1XyqDnDaXoHQ-EEyPI4XFrQHcHOF2hWG": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/fHkl_RuHOoc4rso__nV-qreikovd6Yhrq5mpBlkf5hmPGaxDlik2bYOQ4dhUQjtl")},

			"work": {Mode: fs.ModeDir | 0700},
		}},
	}
	checkWithCache(t, testCases)
}

func TestErrors(t *testing.T) {
	t.Parallel()

	testCases := []struct {
		name string
		err  error
		want string
	}{
		{"InvalidLookupError", pkg.InvalidLookupError{
			0xff, 0xf0,
		}, "attempting to look up non-input artifact __AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"},

		{"InvalidArtifactError", pkg.InvalidArtifactError{
			0xff, 0xfd,
		}, "artifact __0AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA cannot be cured"},

		{"ChecksumMismatchError", &pkg.ChecksumMismatchError{
			Want: (pkg.Checksum)(bytes.Repeat([]byte{
				0x75, 0xe6, 0x9d, 0x6d, 0xe7, 0x9f,
			}, 8)),
		}, "got AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
			" instead of deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef"},

		{"ResponseStatusError", pkg.ResponseStatusError(
			http.StatusNotAcceptable,
		), "the requested URL returned non-OK status: Not Acceptable"},

		{"DisallowedTypeflagError", pkg.DisallowedTypeflagError(
			tar.TypeChar,
		), "disallowed typeflag '3'"},

		{"InvalidFileModeError", pkg.InvalidFileModeError(
			fs.ModeSymlink | 0777,
		), "artifact did not produce a regular file or directory"},

		{"NoOutputError", pkg.NoOutputError{
			// empty struct
		}, "artifact cured successfully but did not produce any output"},

		{"IRKindError", &pkg.IRKindError{
			Got:       pkg.IRKindEnd,
			Want:      pkg.IRKindIdent,
			Ancillary: 0xcafebabe,
		}, "got terminator IR value (0xcafebabe) instead of ident"},
		{"IRKindError invalid", &pkg.IRKindError{
			Got:       0xbeef,
			Want:      pkg.IRKindIdent,
			Ancillary: 0xcafe,
		}, "got invalid kind 48879 IR value (0xcafe) instead of ident"},

		{"UnsupportedVariantError", pkg.UnsupportedVariantError(
			"rosa",
		), `unsupported variant "rosa"`},

		{"UnsupportedArchError zero", pkg.UnsupportedArchError(""),
			"invalid architecture name"},
		{"UnsupportedArchError", pkg.UnsupportedArchError("riscv64"),
			"unsupported architecture riscv64"},
	}
	for _, tc := range testCases {
		t.Run(tc.name, func(t *testing.T) {
			t.Parallel()

			if got := tc.err.Error(); got != tc.want {
				t.Errorf("Error: %q, want %q", got, tc.want)
			}
		})
	}
}

func TestScrubError(t *testing.T) {
	t.Parallel()

	testCases := []struct {
		name   string
		err    pkg.ScrubError
		want   string
		unwrap []error
	}{
		{"sample", *newWantScrubError(
			fhs.AbsVarLib.Append("cure"),
		), `checksum mismatches:
got vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX instead of _wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

dangling identifiers:
_gAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
_v4AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
_v8AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

errors during scrub:
  /var/lib/cure/checksum/__8AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA:
    artifact did not produce a regular file or directory
  /var/lib/cure/checksum/invalid:
    illegal base64 data at input byte 4
  /var/lib/cure/identifier/_v8AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA:
    readlink /var/lib/cure/identifier/_v8AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: invalid argument
  /var/lib/cure/identifier/invalid:
    illegal base64 data at input byte 4
  /var/lib/cure/nonexistent:
    illegal base64 data at input byte 8
`, []error{
			&pkg.ChecksumMismatchError{Got: pkg.MustDecode(
				"vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX",
			), Want: pkg.Checksum{0xff, 0}},

			pkg.InvalidFileModeError(fs.ModeSymlink),
			base64.CorruptInputError(4),

			&os.PathError{
				Op: "readlink",
				Path: fhs.AbsVarLib.Append("cure").Append(
					"identifier",
					pkg.Encode(pkg.ID{0xfe, 0xff}),
				).String(),
				Err: syscall.EINVAL,
			},

			base64.CorruptInputError(4),
			base64.CorruptInputError(8),
		}},

		{"full", pkg.ScrubError{
			ChecksumMismatches: []pkg.ChecksumMismatchError{
				{Want: pkg.MustDecode("CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN")},
			},
			DanglingIdentifiers: []pkg.ID{
				(pkg.ID)(bytes.Repeat([]byte{0x75, 0xe6, 0x9d, 0x6d, 0xe7, 0x9f}, 8)),
				(pkg.ID)(bytes.Repeat([]byte{0x71, 0xa7, 0xde, 0x6d, 0xa6, 0xde}, 8)),
			},
			Errs: map[unique.Handle[string]][]error{
				unique.Make("/proc/nonexistent"): {
					stub.UniqueError(0xcafe),
					stub.UniqueError(0xbad),
					stub.UniqueError(0xff),
				},
			},
		}, `checksum mismatches:
got AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA instead of CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN

dangling identifiers:
deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef
cafebabecafebabecafebabecafebabecafebabecafebabecafebabecafebabe

errors during scrub:
  /proc/nonexistent:
    unique error 51966 injected by the test suite
    unique error 2989 injected by the test suite
    unique error 255 injected by the test suite
`, []error{
			&pkg.ChecksumMismatchError{Want: pkg.MustDecode("CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN")},
			stub.UniqueError(0xcafe),
			stub.UniqueError(0xbad),
			stub.UniqueError(0xff),
		}},
	}
	for _, tc := range testCases {
		t.Run(tc.name, func(t *testing.T) {
			t.Parallel()

			if got := tc.err.Error(); got != tc.want {
				t.Errorf("Error:\n\n%s\n\nwant\n\n%s", got, tc.want)
			}

			if unwrap := tc.err.Unwrap(); !reflect.DeepEqual(unwrap, tc.unwrap) {
				t.Errorf("Unwrap: %#v, want %#v", unwrap, tc.unwrap)
			}
		})
	}
}

func TestDependencyCureError(t *testing.T) {
	t.Parallel()

	makeIdent := func(ident ...byte) pkg.Artifact {
		var a overrideIdent
		copy(a.id[:], ident)
		// does not compare equal
		a.TrivialArtifact = new(stubArtifact)
		return a
	}

	testCases := []struct {
		name   string
		err    pkg.DependencyCureError
		want   string
		unwrap []error
	}{
		{"simple", pkg.DependencyCureError{
			{A: makeIdent(0xff, 9), Err: stub.UniqueError(0xbad09)},
			{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
			{A: makeIdent(0xff, 0xf), Err: stub.UniqueError(0xbad0f)},
			{A: makeIdent(0xff, 1), Err: stub.UniqueError(0xbad01)},
		}, `errors curing dependencies:
	_wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765184 injected by the test suite
	_wEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765185 injected by the test suite
	_wkAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765193 injected by the test suite
	_w8AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765199 injected by the test suite`, []error{
			&pkg.CureError{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
			&pkg.CureError{A: makeIdent(0xff, 1), Err: stub.UniqueError(0xbad01)},
			&pkg.CureError{A: makeIdent(0xff, 9), Err: stub.UniqueError(0xbad09)},
			&pkg.CureError{A: makeIdent(0xff, 0xf), Err: stub.UniqueError(0xbad0f)},
		}},

		{"dedup", pkg.DependencyCureError{
			{A: makeIdent(0xff, 9), Err: stub.UniqueError(0xbad09)},
			{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
			{A: makeIdent(0xff, 0xfd), Err: &pkg.DependencyCureError{
				{A: makeIdent(0xff, 9), Err: stub.UniqueError(0xbad09)},
				{A: makeIdent(0xff, 0xc), Err: &pkg.DependencyCureError{
					{A: makeIdent(0xff, 0xf), Err: stub.UniqueError(0xbad0f)},
					{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
				}},
				{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
				{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
			}},
			{A: makeIdent(0xff, 0xff), Err: &pkg.DependencyCureError{
				{A: makeIdent(0xff, 9), Err: stub.UniqueError(0xbad09)},
				{A: makeIdent(0xff, 0xc), Err: &pkg.DependencyCureError{
					{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
				}},
				{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
			}},
			{A: makeIdent(0xff, 0xf), Err: stub.UniqueError(0xbad0f)},
			{A: makeIdent(0xff, 1), Err: stub.UniqueError(0xbad01)},
		}, `errors curing dependencies:
	_wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765184 injected by the test suite
	_wEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765185 injected by the test suite
	_wkAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765193 injected by the test suite
	_w8AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765199 injected by the test suite`, []error{
			&pkg.CureError{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
			&pkg.CureError{A: makeIdent(0xff, 1), Err: stub.UniqueError(0xbad01)},
			&pkg.CureError{A: makeIdent(0xff, 9), Err: stub.UniqueError(0xbad09)},
			&pkg.CureError{A: makeIdent(0xff, 0xf), Err: stub.UniqueError(0xbad0f)},
		}},
	}
	for _, tc := range testCases {
		t.Run(tc.name, func(t *testing.T) {
			t.Parallel()

			if got := tc.err.Error(); got != tc.want {
				t.Errorf("Error:\n%s\nwant\n%s", got, tc.want)
			}

			if unwrap := tc.err.Unwrap(); !reflect.DeepEqual(unwrap, tc.unwrap) {
				t.Errorf("Unwrap: %#v, want %#v", unwrap, tc.unwrap)
			}
		})
	}
}

// earlyFailureF is a [FloodArtifact] with a large dependency graph resulting in
// a large [DependencyCureError].
type earlyFailureF int

func (earlyFailureF) Kind() pkg.Kind       { return pkg.KindExec }
func (earlyFailureF) Params(*pkg.IContext) {}
func (earlyFailureF) IsExclusive() bool    { return false }

func (a earlyFailureF) Inputs() []pkg.Artifact {
	deps := make([]pkg.Artifact, a)
	for i := range deps {
		deps[i] = a - 1
	}
	return deps
}

func (a earlyFailureF) Cure(*pkg.FContext) error {
	if a != 0 {
		panic("unexpected cure on " + strconv.Itoa(int(a)))
	}
	return stub.UniqueError(0xcafe)
}

func BenchmarkEarlyDCE(b *testing.B) {
	msg := message.New(log.New(os.Stderr, "dce: ", 0))
	msg.SwapVerbose(testing.Verbose())
	c, err := pkg.Open(b.Context(), msg, check.MustAbs(b.TempDir()), nil)
	if err != nil {
		b.Fatal(err)
	}
	_, _, err = c.Cure(earlyFailureF(8))
	if !errors.Is(err, stub.UniqueError(0xcafe)) {
		b.Fatalf("Cure: error = %v", err)
	}
	c.Close()
	dce := err.(*pkg.DependencyCureError)

	for b.Loop() {
		dce.Unwrap()
	}
}

func TestDependencyCureErrorEarly(t *testing.T) {
	t.Parallel()

	checkWithCache(t, []cacheTestCase{
		{"early", 0, nil, func(t *testing.T, _ *check.Absolute, c *pkg.Cache) {
			_, _, err := c.Cure(earlyFailureF(8))
			if !errors.Is(err, stub.UniqueError(0xcafe)) {
				t.Fatalf("Cure: error = %v", err)
			}
		}, expectsFS{
			".":          {Mode: fs.ModeDir | 0700},
			"checksum":   {Mode: fs.ModeDir | 0700},
			"identifier": {Mode: fs.ModeDir | 0700},
			"substitute": {Mode: fs.ModeDir | 0700},
			"work":       {Mode: fs.ModeDir | 0700},
		}},
	})
}

func TestOpen(t *testing.T) {
	t.Parallel()

	t.Run("nonexistent", func(t *testing.T) {
		t.Parallel()

		wantErr := &os.PathError{
			Op:   "mkdir",
			Path: container.Nonexistent,
			Err:  syscall.ENOENT,
		}
		if _, err := pkg.Open(
			t.Context(),
			message.New(nil),
			check.MustAbs(container.Nonexistent),
			nil,
		); !reflect.DeepEqual(err, wantErr) {
			t.Errorf("Open: error = %#v, want %#v", err, wantErr)
		}
	})

	t.Run("permission", func(t *testing.T) {
		t.Parallel()

		tempDir := check.MustAbs(t.TempDir())
		if err := os.Chmod(tempDir.String(), 0); err != nil {
			t.Fatal(err)
		} else {
			t.Cleanup(func() {
				if err = os.Chmod(tempDir.String(), 0700); err != nil {
					t.Fatal(err)
				}
			})
		}

		wantErr := &os.PathError{
			Op:   "mkdir",
			Path: tempDir.Append("cache").String(),
			Err:  syscall.EACCES,
		}
		if _, err := pkg.Open(
			t.Context(),
			message.New(nil),
			tempDir.Append("cache"),
			nil,
		); !reflect.DeepEqual(err, wantErr) {
			t.Errorf("Open: error = %#v, want %#v", err, wantErr)
		}
	})

	t.Run("dirty", func(t *testing.T) {
		t.Parallel()

		tempDir := check.MustAbs(t.TempDir())
		if err := os.MkdirAll(tempDir.Append(
			"cache",
			"work",
			"dirty",
		).String(), 0755); err != nil {
			t.Fatal(err)
		}

		wantErr := errors.New("work is not empty, scrub likely required")
		if _, err := pkg.Open(
			t.Context(),
			message.New(nil),
			tempDir.Append("cache"),
			nil,
		); !reflect.DeepEqual(err, wantErr) {
			t.Errorf("Open: error = %#v, want %#v", err, wantErr)
		}
	})

	t.Run("scratch", func(t *testing.T) {
		t.Parallel()

		tempDir := check.MustAbs(t.TempDir())
		if err := os.MkdirAll(tempDir.Append(
			"cache",
			"scratch",
		).String(), 0755); err != nil {
			t.Fatal(err)
		}

		wantErr := errors.New("scratch is present, scrub likely required")
		if _, err := pkg.Open(
			t.Context(),
			message.New(nil),
			tempDir.Append("cache"), nil,
		); !reflect.DeepEqual(err, wantErr) {
			t.Errorf("Open: error = %#v, want %#v", err, wantErr)
		}
	})
}

func TestExtensionRegister(t *testing.T) {
	extensionOld := extension
	openedOld := opened
	t.Cleanup(func() { extension = extensionOld; opened = openedOld })
	extension = ""
	opened = false

	t.Run("set", func(t *testing.T) {
		t.Cleanup(func() { extension = "" })

		const want = "rosa"
		pkg.SetExtension(want)
		if got := pkg.Extension(); got != want {
			t.Fatalf("Extension: %q, want %q", got, want)
		}
	})

	t.Run("twice", func(t *testing.T) {
		t.Cleanup(func() { extension = "" })

		defer func() {
			const wantPanic = "attempting to set extension twice"
			if r := recover(); r != wantPanic {
				t.Errorf("panic: %#v, want %q", r, wantPanic)
			}
		}()
		pkg.SetExtension("rosa")
		pkg.SetExtension("rosa")
	})

	t.Run("invalid", func(t *testing.T) {
		defer func() {
			var wantPanic = pkg.ErrInvalidExtension
			if r := recover(); r != wantPanic {
				t.Errorf("panic: %#v, want %#v", r, wantPanic)
			}
		}()
		pkg.SetExtension(" ")
	})

	t.Run("opened", func(t *testing.T) {
		t.Cleanup(func() { opened = false })

		if _, err := pkg.Open(
			t.Context(),
			message.New(log.Default()),
			check.MustAbs(container.Nonexistent),
			nil,
		); !errors.Is(err, os.ErrNotExist) {
			t.Fatalf("Open: error = %v", err)
		}

		t.Run("variant", func(t *testing.T) {
			defer func() {
				const wantPanic = "attempting to set extension after open"
				if r := recover(); r != wantPanic {
					t.Errorf("panic: %#v, want %q", r, wantPanic)
				}
			}()
			pkg.SetExtension("rosa")
		})

		t.Run("register", func(t *testing.T) {
			defer func() {
				const wantPanic = "attempting to register after open"
				if r := recover(); r != wantPanic {
					t.Errorf("panic: %#v, want %q", r, wantPanic)
				}
			}()
			pkg.Register(pkg.KindCustomOffset, nil)
		})
	})

	t.Run("incomplete", func(t *testing.T) {
		t.Cleanup(func() { delete(irArtifact, pkg.KindCustomOffset) })

		defer func() {
			const wantPanic = "attempting to open cache with incomplete variant setup"
			if r := recover(); r != wantPanic {
				t.Errorf("panic: %#v, want %q", r, wantPanic)
			}
		}()
		pkg.Register(pkg.KindCustomOffset, nil)

		t.Cleanup(func() { opened = false })
		_, _ = pkg.Open(nil, nil, nil, nil)
		panic("unreachable")
	})

	t.Run("create", func(t *testing.T) {
		t.Cleanup(func() { extension = "" })
		const want = "rosa"
		pkg.SetExtension(want)

		base := check.MustAbs(t.TempDir())
		t.Cleanup(func() { opened = false })
		if c, err := pkg.Open(t.Context(), nil, base, nil); err != nil {
			t.Fatal(err)
		} else {
			c.Close()
		}

		if got, err := os.ReadFile(base.Append("variant").String()); err != nil {
			t.Fatal(err)
		} else if string(got) != want {
			t.Fatalf("variant: %q", string(got))
		}
	})

	t.Run("access", func(t *testing.T) {
		base := check.MustAbs(t.TempDir())
		t.Cleanup(func() { opened = false })

		if err := os.WriteFile(base.Append("variant").String(), nil, 0); err != nil {
			t.Fatal(err)
		}

		wantErr := &os.PathError{
			Op:   "open",
			Path: base.Append("variant").String(),
			Err:  syscall.EACCES,
		}
		if _, err := pkg.Open(
			t.Context(), nil,
			base, nil,
		); !reflect.DeepEqual(err, wantErr) {
			t.Fatalf("Open: error = %v, want %v", err, wantErr)
		}
	})

	t.Run("promote", func(t *testing.T) {
		t.Cleanup(func() { extension = "" })
		const want = "rosa"
		pkg.SetExtension(want)

		base := check.MustAbs(t.TempDir())
		t.Cleanup(func() { opened = false })

		variantPath := base.Append("variant")
		if err := os.WriteFile(variantPath.String(), nil, 0600); err != nil {
			t.Fatal(err)
		}

		if _, err := pkg.Open(
			t.Context(), nil,
			base,
			nil,
		); !reflect.DeepEqual(err, pkg.ErrWouldPromote) {
			t.Fatalf("Open: error = %v", err)
		}

		if p, err := os.ReadFile(variantPath.String()); err != nil {
			t.Fatal(err)
		} else if len(p) != 0 {
			t.Fatalf("variant: %q", string(p))
		}

		if c, err := pkg.Open(
			t.Context(), nil,
			base, &pkg.CacheAttr{Flags: pkg.CPromoteVariant},
		); err != nil {
			t.Fatalf("Open: error = %v", err)
		} else {
			c.Close()
		}

		if p, err := os.ReadFile(variantPath.String()); err != nil {
			t.Fatal(err)
		} else if string(p) != want {
			t.Fatalf("variant: %q, want %q", string(p), want)
		}
	})

	t.Run("open invalid", func(t *testing.T) {
		base := check.MustAbs(t.TempDir())
		t.Cleanup(func() { opened = false })

		variantPath := base.Append("variant")
		if err := os.WriteFile(variantPath.String(), make([]byte, 129), 0400); err != nil {
			t.Fatal(err)
		}

		if _, err := pkg.Open(
			t.Context(), nil,
			base, nil,
		); !reflect.DeepEqual(err, pkg.ErrInvalidExtension) {
			t.Fatalf("Open: error = %v", err)
		}
	})

	t.Run("unsupported", func(t *testing.T) {
		base := check.MustAbs(t.TempDir())
		t.Cleanup(func() { opened = false })

		variantPath := base.Append("variant")
		if err := os.WriteFile(variantPath.String(), []byte("rosa"), 0400); err != nil {
			t.Fatal(err)
		}

		if _, err := pkg.Open(
			t.Context(), nil,
			base, nil,
		); !reflect.DeepEqual(err, pkg.UnsupportedVariantError("rosa")) {
			t.Fatalf("Open: error = %v", err)
		}
	})
}