From ae2df2c450dd655b93a950124b6ab16e2b4d967b Mon Sep 17 00:00:00 2001
From: Ophestra <cat@gensokyo.uk>
Date: Thu, 25 Sep 2025 13:46:21 +0900
Subject: [PATCH] internal: remove sys package

This package is replaced by container/stub. Remove and replace it with unexported implementation for the upcoming test suite rewrite.

Signed-off-by: Ophestra <cat@gensokyo.uk>
---
 cmd/hakurei/command.go                |  11 +-
 cmd/hakurei/main.go                   |   3 -
 cmd/hakurei/parse.go                  |   5 +-
 cmd/hakurei/print.go                  |   8 +-
 internal/app/app.go                   |   8 +-
 internal/app/app_stub_test.go         | 221 +++++++++++++++++---------
 internal/app/app_test.go              |  91 ++++++-----
 internal/app/container.go             |  41 ++---
 internal/app/dispatcher.go            |  99 ++++++++++++
 internal/app/export_test.go           |  16 --
 internal/app/{seal.go => finalise.go} | 203 +++++++++++------------
 internal/{sys => app}/hsu.go          |  40 +++--
 internal/app/paths.go                 |  36 +++++
 internal/app/process.go               |  54 +++----
 internal/sys/interface.go             |  76 ---------
 internal/sys/std.go                   |  44 -----
 test/test.py                          |   2 +-
 17 files changed, 516 insertions(+), 442 deletions(-)
 create mode 100644 internal/app/dispatcher.go
 delete mode 100644 internal/app/export_test.go
 rename internal/app/{seal.go => finalise.go} (73%)
 rename internal/{sys => app}/hsu.go (70%)
 create mode 100644 internal/app/paths.go
 delete mode 100644 internal/sys/interface.go
 delete mode 100644 internal/sys/std.go

diff --git a/cmd/hakurei/command.go b/cmd/hakurei/command.go
index 0600a55..1671902 100644
--- a/cmd/hakurei/command.go
+++ b/cmd/hakurei/command.go
@@ -18,7 +18,6 @@ import (
 	"hakurei.app/internal/app"
 	"hakurei.app/internal/app/state"
 	"hakurei.app/internal/hlog"
-	"hakurei.app/internal/sys"
 	"hakurei.app/system"
 	"hakurei.app/system/dbus"
 )
@@ -43,7 +42,7 @@ func buildCommand(ctx context.Context, out io.Writer) command.Command {
 		config := tryPath(args[0])
 		config.Args = append(config.Args, args[1:]...)
 
-		app.Main(ctx, std, config)
+		app.Main(ctx, config)
 		panic("unreachable")
 	})
 
@@ -79,7 +78,7 @@ func buildCommand(ctx context.Context, out io.Writer) command.Command {
 				passwd     *user.User
 				passwdOnce sync.Once
 				passwdFunc = func() {
-					us := strconv.Itoa(sys.MustUid(std, flagIdentity))
+					us := strconv.Itoa(app.HsuUid(new(app.Hsu).MustID(), flagIdentity))
 					if u, err := user.LookupId(us); err != nil {
 						hlog.Verbosef("cannot look up uid %s", us)
 						passwd = &user.User{
@@ -163,7 +162,7 @@ func buildCommand(ctx context.Context, out io.Writer) command.Command {
 				}
 			}
 
-			app.Main(ctx, std, config)
+			app.Main(ctx, config)
 			panic("unreachable")
 		}).
 			Flag(&flagDBusConfigSession, "dbus-config", command.StringFlag("builtin"),
@@ -219,7 +218,9 @@ func buildCommand(ctx context.Context, out io.Writer) command.Command {
 	{
 		var flagShort bool
 		c.NewCommand("ps", "List active instances", func(args []string) error {
-			printPs(os.Stdout, time.Now().UTC(), state.NewMulti(std.Paths().RunDirPath.String()), flagShort, flagJSON)
+			var sc hst.Paths
+			app.CopyPaths(&sc, new(app.Hsu).MustID())
+			printPs(os.Stdout, time.Now().UTC(), state.NewMulti(sc.RunDirPath.String()), flagShort, flagJSON)
 			return errSuccess
 		}).Flag(&flagShort, "short", command.BoolFlag(false), "Print instance id")
 	}
diff --git a/cmd/hakurei/main.go b/cmd/hakurei/main.go
index b71f50c..2b9193b 100644
--- a/cmd/hakurei/main.go
+++ b/cmd/hakurei/main.go
@@ -15,7 +15,6 @@ import (
 	"hakurei.app/container"
 	"hakurei.app/internal"
 	"hakurei.app/internal/hlog"
-	"hakurei.app/internal/sys"
 )
 
 var (
@@ -27,8 +26,6 @@ var (
 
 func init() { hlog.Prepare("hakurei") }
 
-var std sys.State = new(sys.Std)
-
 func main() {
 	// early init path, skips root check and duplicate PR_SET_DUMPABLE
 	container.TryArgv0(hlog.Output{}, hlog.Prepare, internal.InstallOutput)
diff --git a/cmd/hakurei/parse.go b/cmd/hakurei/parse.go
index 56ff83e..897382e 100644
--- a/cmd/hakurei/parse.go
+++ b/cmd/hakurei/parse.go
@@ -11,6 +11,7 @@ import (
 	"syscall"
 
 	"hakurei.app/hst"
+	"hakurei.app/internal/app"
 	"hakurei.app/internal/app/state"
 	"hakurei.app/internal/hlog"
 )
@@ -87,7 +88,9 @@ func tryShort(name string) (config *hst.Config, entry *state.State) {
 	if likePrefix && len(name) >= 8 {
 		hlog.Verbose("argument looks like prefix")
 
-		s := state.NewMulti(std.Paths().RunDirPath.String())
+		var sc hst.Paths
+		app.CopyPaths(&sc, new(app.Hsu).MustID())
+		s := state.NewMulti(sc.RunDirPath.String())
 		if entries, err := state.Join(s); err != nil {
 			log.Printf("cannot join store: %v", err)
 			// drop to fetch from file
diff --git a/cmd/hakurei/print.go b/cmd/hakurei/print.go
index 387b5c2..938517b 100644
--- a/cmd/hakurei/print.go
+++ b/cmd/hakurei/print.go
@@ -12,8 +12,8 @@ import (
 	"time"
 
 	"hakurei.app/hst"
+	"hakurei.app/internal/app"
 	"hakurei.app/internal/app/state"
-	"hakurei.app/internal/sys"
 	"hakurei.app/system/dbus"
 )
 
@@ -21,10 +21,8 @@ func printShowSystem(output io.Writer, short, flagJSON bool) {
 	t := newPrinter(output)
 	defer t.MustFlush()
 
-	info := &hst.Info{
-		Paths: std.Paths(),
-		User:  sys.MustGetUserID(std),
-	}
+	info := &hst.Info{User: new(app.Hsu).MustID()}
+	app.CopyPaths(&info.Paths, info.User)
 
 	if flagJSON {
 		printJSON(output, short, info)
diff --git a/internal/app/app.go b/internal/app/app.go
index 4ecf1cc..b533156 100644
--- a/internal/app/app.go
+++ b/internal/app/app.go
@@ -8,19 +8,17 @@ import (
 
 	"hakurei.app/hst"
 	"hakurei.app/internal/app/state"
-	"hakurei.app/internal/sys"
 )
 
 // Main runs an app according to [hst.Config] and terminates. Main does not return.
-func Main(ctx context.Context, k sys.State, config *hst.Config) {
+func Main(ctx context.Context, config *hst.Config) {
 	var id state.ID
 	if err := state.NewAppID(&id); err != nil {
 		log.Fatal(err)
 	}
 
-	var seal outcome
-	seal.id = &stringPair[state.ID]{id, id.String()}
-	if err := seal.finalise(ctx, k, config); err != nil {
+	seal := outcome{id: &stringPair[state.ID]{id, id.String()}, syscallDispatcher: direct{}}
+	if err := seal.finalise(ctx, config); err != nil {
 		printMessageError("cannot seal app:", err)
 		os.Exit(1)
 	}
diff --git a/internal/app/app_stub_test.go b/internal/app/app_stub_test.go
index f386eb0..ff21849 100644
--- a/internal/app/app_stub_test.go
+++ b/internal/app/app_stub_test.go
@@ -1,34 +1,24 @@
-package app_test
+package app
 
 import (
 	"fmt"
 	"io/fs"
 	"log"
+	"os/exec"
 	"os/user"
-	"strconv"
-
-	"hakurei.app/hst"
 )
 
-// fs methods are not implemented using a real FS
-// to help better understand filesystem access behaviour
 type stubNixOS struct {
 	lookPathErr map[string]error
 	usernameErr map[string]error
 }
 
-func (s *stubNixOS) Getuid() int                              { return 1971 }
-func (s *stubNixOS) Getgid() int                              { return 100 }
-func (s *stubNixOS) TempDir() string                          { return "/tmp" }
-func (s *stubNixOS) MustExecutable() string                   { return "/run/wrappers/bin/hakurei" }
-func (s *stubNixOS) Exit(code int)                            { panic("called exit on stub with code " + strconv.Itoa(code)) }
-func (s *stubNixOS) EvalSymlinks(path string) (string, error) { return path, nil }
-func (s *stubNixOS) Uid(aid int) (int, error)                 { return 1000000 + 0*10000 + aid, nil }
+func (k *stubNixOS) new(func(k syscallDispatcher)) { panic("not implemented") }
 
-func (s *stubNixOS) Println(v ...any)               { log.Println(v...) }
-func (s *stubNixOS) Printf(format string, v ...any) { log.Printf(format, v...) }
+func (k *stubNixOS) getuid() int { return 1971 }
+func (k *stubNixOS) getgid() int { return 100 }
 
-func (s *stubNixOS) LookupEnv(key string) (string, bool) {
+func (k *stubNixOS) lookupEnv(key string) (string, bool) {
 	switch key {
 	case "SHELL":
 		return "/run/current-system/sw/bin/zsh", true
@@ -40,6 +30,8 @@ func (s *stubNixOS) LookupEnv(key string) (string, bool) {
 		return "", false
 	case "HOME":
 		return "/home/ophestra", true
+	case "XDG_RUNTIME_DIR":
+		return "/run/user/1971", true
 	case "XDG_CONFIG_HOME":
 		return "/home/ophestra/xdg/config", true
 	default:
@@ -47,61 +39,7 @@ func (s *stubNixOS) LookupEnv(key string) (string, bool) {
 	}
 }
 
-func (s *stubNixOS) LookPath(file string) (string, error) {
-	if s.lookPathErr != nil {
-		if err, ok := s.lookPathErr[file]; ok {
-			return "", err
-		}
-	}
-
-	switch file {
-	case "zsh":
-		return "/run/current-system/sw/bin/zsh", nil
-	default:
-		panic(fmt.Sprintf("attempted to look up unexpected executable %q", file))
-	}
-}
-
-func (s *stubNixOS) LookupGroup(name string) (*user.Group, error) {
-	switch name {
-	case "video":
-		return &user.Group{Gid: "26", Name: "video"}, nil
-	default:
-		return nil, user.UnknownGroupError(name)
-	}
-}
-
-func (s *stubNixOS) ReadDir(name string) ([]fs.DirEntry, error) {
-	switch name {
-	case "/":
-		return stubDirEntries("bin", "boot", "dev", "etc", "home", "lib",
-			"lib64", "nix", "proc", "root", "run", "srv", "sys", "tmp", "usr", "var")
-	case "/run":
-		return stubDirEntries("agetty.reload", "binfmt", "booted-system",
-			"credentials", "cryptsetup", "current-system", "dbus", "host", "keys",
-			"libvirt", "libvirtd.pid", "lock", "log", "lvm", "mount", "NetworkManager",
-			"nginx", "nixos", "nscd", "opengl-driver", "pppd", "resolvconf", "sddm",
-			"store", "syncoid", "system", "systemd", "tmpfiles.d", "udev", "udisks2",
-			"user", "utmp", "virtlogd.pid", "wrappers", "zed.pid", "zed.state")
-	case "/etc":
-		return stubDirEntries("alsa", "bashrc", "binfmt.d", "dbus-1", "default",
-			"ethertypes", "fonts", "fstab", "fuse.conf", "group", "host.conf", "hostid",
-			"hostname", "hostname.CHECKSUM", "hosts", "inputrc", "ipsec.d", "issue", "kbd",
-			"libblockdev", "locale.conf", "localtime", "login.defs", "lsb-release", "lvm",
-			"machine-id", "man_db.conf", "modprobe.d", "modules-load.d", "mtab", "nanorc",
-			"netgroup", "NetworkManager", "nix", "nixos", "NIXOS", "nscd.conf", "nsswitch.conf",
-			"opensnitchd", "os-release", "pam", "pam.d", "passwd", "pipewire", "pki", "polkit-1",
-			"profile", "protocols", "qemu", "resolv.conf", "resolvconf.conf", "rpc", "samba",
-			"sddm.conf", "secureboot", "services", "set-environment", "shadow", "shells", "ssh",
-			"ssl", "static", "subgid", "subuid", "sudoers", "sysctl.d", "systemd", "terminfo",
-			"tmpfiles.d", "udev", "udisks2", "UPower", "vconsole.conf", "X11", "zfs", "zinputrc",
-			"zoneinfo", "zprofile", "zshenv", "zshrc")
-	default:
-		panic(fmt.Sprintf("attempted to read unexpected directory %q", name))
-	}
-}
-
-func (s *stubNixOS) Stat(name string) (fs.FileInfo, error) {
+func (k *stubNixOS) stat(name string) (fs.FileInfo, error) {
 	switch name {
 	case "/var/run/nscd":
 		return nil, nil
@@ -118,17 +56,144 @@ func (s *stubNixOS) Stat(name string) (fs.FileInfo, error) {
 	}
 }
 
-func (s *stubNixOS) Open(name string) (fs.File, error) {
+func (k *stubNixOS) readdir(name string) ([]fs.DirEntry, error) {
 	switch name {
+	case "/":
+		return stubDirEntries("bin", "boot", "dev", "etc", "home", "lib",
+			"lib64", "nix", "proc", "root", "run", "srv", "sys", "tmp", "usr", "var")
+
+	case "/run":
+		return stubDirEntries("agetty.reload", "binfmt", "booted-system",
+			"credentials", "cryptsetup", "current-system", "dbus", "host", "keys",
+			"libvirt", "libvirtd.pid", "lock", "log", "lvm", "mount", "NetworkManager",
+			"nginx", "nixos", "nscd", "opengl-driver", "pppd", "resolvconf", "sddm",
+			"store", "syncoid", "system", "systemd", "tmpfiles.d", "udev", "udisks2",
+			"user", "utmp", "virtlogd.pid", "wrappers", "zed.pid", "zed.state")
+
+	case "/etc":
+		return stubDirEntries("alsa", "bashrc", "binfmt.d", "dbus-1", "default",
+			"ethertypes", "fonts", "fstab", "fuse.conf", "group", "host.conf", "hostid",
+			"hostname", "hostname.CHECKSUM", "hosts", "inputrc", "ipsec.d", "issue", "kbd",
+			"libblockdev", "locale.conf", "localtime", "login.defs", "lsb-release", "lvm",
+			"machine-id", "man_db.conf", "modprobe.d", "modules-load.d", "mtab", "nanorc",
+			"netgroup", "NetworkManager", "nix", "nixos", "NIXOS", "nscd.conf", "nsswitch.conf",
+			"opensnitchd", "os-release", "pam", "pam.d", "passwd", "pipewire", "pki", "polkit-1",
+			"profile", "protocols", "qemu", "resolv.conf", "resolvconf.conf", "rpc", "samba",
+			"sddm.conf", "secureboot", "services", "set-environment", "shadow", "shells", "ssh",
+			"ssl", "static", "subgid", "subuid", "sudoers", "sysctl.d", "systemd", "terminfo",
+			"tmpfiles.d", "udev", "udisks2", "UPower", "vconsole.conf", "X11", "zfs", "zinputrc",
+			"zoneinfo", "zprofile", "zshenv", "zshrc")
+
 	default:
-		panic(fmt.Sprintf("attempted to open unexpected file %q", name))
+		panic(fmt.Sprintf("attempted to read unexpected directory %q", name))
 	}
 }
 
-func (s *stubNixOS) Paths() hst.Paths {
-	return hst.Paths{
-		SharePath:   m("/tmp/hakurei.1971"),
-		RuntimePath: m("/run/user/1971"),
-		RunDirPath:  m("/run/user/1971/hakurei"),
+func (k *stubNixOS) tempdir() string { return "/tmp/" }
+
+func (k *stubNixOS) evalSymlinks(path string) (string, error) {
+	switch path {
+	case "/run/user/1971":
+		return "/run/user/1971", nil
+	case "/tmp/hakurei.0":
+		return "/tmp/hakurei.0", nil
+	case "/run/dbus":
+		return "/run/dbus", nil
+	case "/dev/kvm":
+		return "/dev/kvm", nil
+	case "/etc/":
+		return "/etc/", nil
+	case "/bin":
+		return "/bin", nil
+	case "/boot":
+		return "/boot", nil
+	case "/home":
+		return "/home", nil
+	case "/lib":
+		return "/lib", nil
+	case "/lib64":
+		return "/lib64", nil
+	case "/nix":
+		return "/nix", nil
+	case "/root":
+		return "/root", nil
+	case "/run":
+		return "/run", nil
+	case "/srv":
+		return "/srv", nil
+	case "/sys":
+		return "/sys", nil
+	case "/usr":
+		return "/usr", nil
+	case "/var":
+		return "/var", nil
+	case "/dev/dri":
+		return "/dev/dri", nil
+	case "/usr/bin/":
+		return "/usr/bin/", nil
+	case "/nix/store":
+		return "/nix/store", nil
+	case "/run/current-system":
+		return "/nix/store/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-nixos-system-satori-25.05.99999999.aaaaaaa", nil
+	case "/sys/block":
+		return "/sys/block", nil
+	case "/sys/bus":
+		return "/sys/bus", nil
+	case "/sys/class":
+		return "/sys/class", nil
+	case "/sys/dev":
+		return "/sys/dev", nil
+	case "/sys/devices":
+		return "/sys/devices", nil
+	case "/run/opengl-driver":
+		return "/nix/store/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-graphics-drivers", nil
+	case "/var/lib/persist/module/hakurei/0/1":
+		return "/var/lib/persist/module/hakurei/0/1", nil
+	default:
+		panic(fmt.Sprintf("attempted to evaluate unexpected path %q", path))
 	}
 }
+
+func (k *stubNixOS) lookPath(file string) (string, error) {
+	if k.lookPathErr != nil {
+		if err, ok := k.lookPathErr[file]; ok {
+			return "", err
+		}
+	}
+
+	switch file {
+	case "zsh":
+		return "/run/current-system/sw/bin/zsh", nil
+	default:
+		panic(fmt.Sprintf("attempted to look up unexpected executable %q", file))
+	}
+}
+
+func (k *stubNixOS) lookupGroupId(name string) (string, error) {
+	switch name {
+	case "video":
+		return "26", nil
+	default:
+		return "", user.UnknownGroupError(name)
+	}
+}
+
+func (k *stubNixOS) cmdOutput(cmd *exec.Cmd) ([]byte, error) {
+	switch cmd.Path {
+	case "/proc/nonexistent/hsu":
+		return []byte{'0'}, nil
+	default:
+		panic(fmt.Sprintf("unexpected cmd %#v", cmd))
+	}
+}
+
+func (k *stubNixOS) overflowUid() int { return 65534 }
+func (k *stubNixOS) overflowGid() int { return 65534 }
+
+func (k *stubNixOS) mustHsuPath() string { return "/proc/nonexistent/hsu" }
+
+func (k *stubNixOS) fatalf(format string, v ...any) { panic(fmt.Sprintf(format, v...)) }
+
+func (k *stubNixOS) isVerbose() bool                  { return true }
+func (k *stubNixOS) verbose(v ...any)                 { log.Print(v...) }
+func (k *stubNixOS) verbosef(format string, v ...any) { log.Printf(format, v...) }
diff --git a/internal/app/app_test.go b/internal/app/app_test.go
index 9da7239..005b721 100644
--- a/internal/app/app_test.go
+++ b/internal/app/app_test.go
@@ -1,4 +1,4 @@
-package app_test
+package app
 
 import (
 	"context"
@@ -13,9 +13,7 @@ import (
 	"hakurei.app/container"
 	"hakurei.app/container/seccomp"
 	"hakurei.app/hst"
-	"hakurei.app/internal/app"
 	"hakurei.app/internal/app/state"
-	"hakurei.app/internal/sys"
 	"hakurei.app/system"
 	"hakurei.app/system/acl"
 	"hakurei.app/system/dbus"
@@ -24,7 +22,7 @@ import (
 func TestApp(t *testing.T) {
 	testCases := []struct {
 		name       string
-		os         sys.State
+		k          syscallDispatcher
 		config     *hst.Config
 		id         state.ID
 		wantSys    *system.I
@@ -40,11 +38,11 @@ func TestApp(t *testing.T) {
 				0xb9, 0xa6, 0x07, 0xac,
 			},
 			system.New(context.TODO(), 1000000).
-				Ensure("/tmp/hakurei.1971", 0711).
-				Ensure("/tmp/hakurei.1971/runtime", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/runtime", acl.Execute).
-				Ensure("/tmp/hakurei.1971/runtime/0", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/runtime/0", acl.Read, acl.Write, acl.Execute).
-				Ensure("/tmp/hakurei.1971/tmpdir", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/tmpdir", acl.Execute).
-				Ensure("/tmp/hakurei.1971/tmpdir/0", 01700).UpdatePermType(system.User, "/tmp/hakurei.1971/tmpdir/0", acl.Read, acl.Write, acl.Execute),
+				Ensure("/tmp/hakurei.0", 0711).
+				Ensure("/tmp/hakurei.0/runtime", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/runtime", acl.Execute).
+				Ensure("/tmp/hakurei.0/runtime/0", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/runtime/0", acl.Read, acl.Write, acl.Execute).
+				Ensure("/tmp/hakurei.0/tmpdir", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/tmpdir", acl.Execute).
+				Ensure("/tmp/hakurei.0/tmpdir/0", 01700).UpdatePermType(system.User, "/tmp/hakurei.0/tmpdir/0", acl.Read, acl.Write, acl.Execute),
 			&container.Params{
 				Dir:  m("/home/chronos"),
 				Path: m("/run/current-system/sw/bin/zsh"),
@@ -71,8 +69,8 @@ func TestApp(t *testing.T) {
 					Tmpfs(m("/run/dbus"), 8192, 0755).
 					Remount(m("/dev/"), syscall.MS_RDONLY).
 					Tmpfs(m("/run/user/"), 4096, 0755).
-					Bind(m("/tmp/hakurei.1971/runtime/0"), m("/run/user/65534"), container.BindWritable).
-					Bind(m("/tmp/hakurei.1971/tmpdir/0"), m("/tmp/"), container.BindWritable).
+					Bind(m("/tmp/hakurei.0/runtime/0"), m("/run/user/65534"), container.BindWritable).
+					Bind(m("/tmp/hakurei.0/tmpdir/0"), m("/tmp/"), container.BindWritable).
 					Place(m("/etc/passwd"), []byte("chronos:x:65534:65534:Hakurei:/home/chronos:/run/current-system/sw/bin/zsh\n")).
 					Place(m("/etc/group"), []byte("hakurei:x:65534:\n")).
 					Remount(m("/"), syscall.MS_RDONLY),
@@ -132,19 +130,19 @@ func TestApp(t *testing.T) {
 				0x9b, 0x64, 0xce, 0x7c,
 			},
 			system.New(context.TODO(), 1000009).
-				Ensure("/tmp/hakurei.1971", 0711).
-				Ensure("/tmp/hakurei.1971/runtime", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/runtime", acl.Execute).
-				Ensure("/tmp/hakurei.1971/runtime/9", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/runtime/9", acl.Read, acl.Write, acl.Execute).
-				Ensure("/tmp/hakurei.1971/tmpdir", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/tmpdir", acl.Execute).
-				Ensure("/tmp/hakurei.1971/tmpdir/9", 01700).UpdatePermType(system.User, "/tmp/hakurei.1971/tmpdir/9", acl.Read, acl.Write, acl.Execute).
-				Ephemeral(system.Process, "/tmp/hakurei.1971/ebf083d1b175911782d413369b64ce7c", 0711).
-				Wayland(new(*os.File), "/tmp/hakurei.1971/ebf083d1b175911782d413369b64ce7c/wayland", "/run/user/1971/wayland-0", "org.chromium.Chromium", "ebf083d1b175911782d413369b64ce7c").
+				Ensure("/tmp/hakurei.0", 0711).
+				Ensure("/tmp/hakurei.0/runtime", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/runtime", acl.Execute).
+				Ensure("/tmp/hakurei.0/runtime/9", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/runtime/9", acl.Read, acl.Write, acl.Execute).
+				Ensure("/tmp/hakurei.0/tmpdir", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/tmpdir", acl.Execute).
+				Ensure("/tmp/hakurei.0/tmpdir/9", 01700).UpdatePermType(system.User, "/tmp/hakurei.0/tmpdir/9", acl.Read, acl.Write, acl.Execute).
+				Ephemeral(system.Process, "/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c", 0711).
+				Wayland(new(*os.File), "/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/wayland", "/run/user/1971/wayland-0", "org.chromium.Chromium", "ebf083d1b175911782d413369b64ce7c").
 				Ensure("/run/user/1971/hakurei", 0700).UpdatePermType(system.User, "/run/user/1971/hakurei", acl.Execute).
 				Ensure("/run/user/1971", 0700).UpdatePermType(system.User, "/run/user/1971", acl.Execute). // this is ordered as is because the previous Ensure only calls mkdir if XDG_RUNTIME_DIR is unset
 				Ephemeral(system.Process, "/run/user/1971/hakurei/ebf083d1b175911782d413369b64ce7c", 0700).UpdatePermType(system.Process, "/run/user/1971/hakurei/ebf083d1b175911782d413369b64ce7c", acl.Execute).
 				Link("/run/user/1971/pulse/native", "/run/user/1971/hakurei/ebf083d1b175911782d413369b64ce7c/pulse").
 				CopyFile(new([]byte), "/home/ophestra/xdg/config/pulse/cookie", 256, 256).
-				MustProxyDBus("/tmp/hakurei.1971/ebf083d1b175911782d413369b64ce7c/bus", &dbus.Config{
+				MustProxyDBus("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/bus", &dbus.Config{
 					Talk: []string{
 						"org.freedesktop.Notifications",
 						"org.freedesktop.FileManager1",
@@ -166,7 +164,7 @@ func TestApp(t *testing.T) {
 						"org.freedesktop.portal.*": "@/org/freedesktop/portal/*",
 					},
 					Filter: true,
-				}, "/tmp/hakurei.1971/ebf083d1b175911782d413369b64ce7c/system_bus_socket", &dbus.Config{
+				}, "/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/system_bus_socket", &dbus.Config{
 					Talk: []string{
 						"org.bluez",
 						"org.freedesktop.Avahi",
@@ -174,8 +172,8 @@ func TestApp(t *testing.T) {
 					},
 					Filter: true,
 				}).
-				UpdatePerm("/tmp/hakurei.1971/ebf083d1b175911782d413369b64ce7c/bus", acl.Read, acl.Write).
-				UpdatePerm("/tmp/hakurei.1971/ebf083d1b175911782d413369b64ce7c/system_bus_socket", acl.Read, acl.Write),
+				UpdatePerm("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/bus", acl.Read, acl.Write).
+				UpdatePerm("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/system_bus_socket", acl.Read, acl.Write),
 			&container.Params{
 				Dir:  m("/home/chronos"),
 				Path: m("/run/current-system/sw/bin/zsh"),
@@ -208,15 +206,15 @@ func TestApp(t *testing.T) {
 					Tmpfs(m("/run/dbus"), 8192, 0755).
 					Remount(m("/dev/"), syscall.MS_RDONLY).
 					Tmpfs(m("/run/user/"), 4096, 0755).
-					Bind(m("/tmp/hakurei.1971/runtime/9"), m("/run/user/65534"), container.BindWritable).
-					Bind(m("/tmp/hakurei.1971/tmpdir/9"), m("/tmp/"), container.BindWritable).
+					Bind(m("/tmp/hakurei.0/runtime/9"), m("/run/user/65534"), container.BindWritable).
+					Bind(m("/tmp/hakurei.0/tmpdir/9"), m("/tmp/"), container.BindWritable).
 					Place(m("/etc/passwd"), []byte("chronos:x:65534:65534:Hakurei:/home/chronos:/run/current-system/sw/bin/zsh\n")).
 					Place(m("/etc/group"), []byte("hakurei:x:65534:\n")).
-					Bind(m("/tmp/hakurei.1971/ebf083d1b175911782d413369b64ce7c/wayland"), m("/run/user/65534/wayland-0"), 0).
+					Bind(m("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/wayland"), m("/run/user/65534/wayland-0"), 0).
 					Bind(m("/run/user/1971/hakurei/ebf083d1b175911782d413369b64ce7c/pulse"), m("/run/user/65534/pulse/native"), 0).
 					Place(m(hst.Tmp+"/pulse-cookie"), nil).
-					Bind(m("/tmp/hakurei.1971/ebf083d1b175911782d413369b64ce7c/bus"), m("/run/user/65534/bus"), 0).
-					Bind(m("/tmp/hakurei.1971/ebf083d1b175911782d413369b64ce7c/system_bus_socket"), m("/run/dbus/system_bus_socket"), 0).
+					Bind(m("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/bus"), m("/run/user/65534/bus"), 0).
+					Bind(m("/tmp/hakurei.0/ebf083d1b175911782d413369b64ce7c/system_bus_socket"), m("/run/dbus/system_bus_socket"), 0).
 					Remount(m("/"), syscall.MS_RDONLY),
 				SeccompPresets: seccomp.PresetExt | seccomp.PresetDenyDevel,
 				HostNet:        true,
@@ -283,19 +281,19 @@ func TestApp(t *testing.T) {
 				0xb4, 0x6e, 0xb5, 0xc1,
 			},
 			system.New(context.TODO(), 1000001).
-				Ensure("/tmp/hakurei.1971", 0711).
-				Ensure("/tmp/hakurei.1971/runtime", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/runtime", acl.Execute).
-				Ensure("/tmp/hakurei.1971/runtime/1", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/runtime/1", acl.Read, acl.Write, acl.Execute).
-				Ensure("/tmp/hakurei.1971/tmpdir", 0700).UpdatePermType(system.User, "/tmp/hakurei.1971/tmpdir", acl.Execute).
-				Ensure("/tmp/hakurei.1971/tmpdir/1", 01700).UpdatePermType(system.User, "/tmp/hakurei.1971/tmpdir/1", acl.Read, acl.Write, acl.Execute).
+				Ensure("/tmp/hakurei.0", 0711).
+				Ensure("/tmp/hakurei.0/runtime", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/runtime", acl.Execute).
+				Ensure("/tmp/hakurei.0/runtime/1", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/runtime/1", acl.Read, acl.Write, acl.Execute).
+				Ensure("/tmp/hakurei.0/tmpdir", 0700).UpdatePermType(system.User, "/tmp/hakurei.0/tmpdir", acl.Execute).
+				Ensure("/tmp/hakurei.0/tmpdir/1", 01700).UpdatePermType(system.User, "/tmp/hakurei.0/tmpdir/1", acl.Read, acl.Write, acl.Execute).
 				Ensure("/run/user/1971/hakurei", 0700).UpdatePermType(system.User, "/run/user/1971/hakurei", acl.Execute).
 				Ensure("/run/user/1971", 0700).UpdatePermType(system.User, "/run/user/1971", acl.Execute). // this is ordered as is because the previous Ensure only calls mkdir if XDG_RUNTIME_DIR is unset
 				UpdatePermType(system.EWayland, "/run/user/1971/wayland-0", acl.Read, acl.Write, acl.Execute).
 				Ephemeral(system.Process, "/run/user/1971/hakurei/8e2c76b066dabe574cf073bdb46eb5c1", 0700).UpdatePermType(system.Process, "/run/user/1971/hakurei/8e2c76b066dabe574cf073bdb46eb5c1", acl.Execute).
 				Link("/run/user/1971/pulse/native", "/run/user/1971/hakurei/8e2c76b066dabe574cf073bdb46eb5c1/pulse").
 				CopyFile(nil, "/home/ophestra/xdg/config/pulse/cookie", 256, 256).
-				Ephemeral(system.Process, "/tmp/hakurei.1971/8e2c76b066dabe574cf073bdb46eb5c1", 0711).
-				MustProxyDBus("/tmp/hakurei.1971/8e2c76b066dabe574cf073bdb46eb5c1/bus", &dbus.Config{
+				Ephemeral(system.Process, "/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1", 0711).
+				MustProxyDBus("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/bus", &dbus.Config{
 					Talk: []string{
 						"org.freedesktop.FileManager1", "org.freedesktop.Notifications",
 						"org.freedesktop.ScreenSaver", "org.freedesktop.secrets",
@@ -308,7 +306,7 @@ func TestApp(t *testing.T) {
 					},
 					Call: map[string]string{}, Broadcast: map[string]string{},
 					Filter: true,
-				}, "/tmp/hakurei.1971/8e2c76b066dabe574cf073bdb46eb5c1/system_bus_socket", &dbus.Config{
+				}, "/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/system_bus_socket", &dbus.Config{
 					Talk: []string{
 						"org.bluez",
 						"org.freedesktop.Avahi",
@@ -316,8 +314,8 @@ func TestApp(t *testing.T) {
 					},
 					Filter: true,
 				}).
-				UpdatePerm("/tmp/hakurei.1971/8e2c76b066dabe574cf073bdb46eb5c1/bus", acl.Read, acl.Write).
-				UpdatePerm("/tmp/hakurei.1971/8e2c76b066dabe574cf073bdb46eb5c1/system_bus_socket", acl.Read, acl.Write),
+				UpdatePerm("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/bus", acl.Read, acl.Write).
+				UpdatePerm("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/system_bus_socket", acl.Read, acl.Write),
 			&container.Params{
 				Uid:  1971,
 				Gid:  100,
@@ -358,15 +356,15 @@ func TestApp(t *testing.T) {
 					Bind(m("/var/lib/persist/module/hakurei/0/1"), m("/var/lib/persist/module/hakurei/0/1"), container.BindWritable|container.BindEnsure).
 					Remount(m("/dev/"), syscall.MS_RDONLY).
 					Tmpfs(m("/run/user/"), 4096, 0755).
-					Bind(m("/tmp/hakurei.1971/runtime/1"), m("/run/user/1971"), container.BindWritable).
-					Bind(m("/tmp/hakurei.1971/tmpdir/1"), m("/tmp/"), container.BindWritable).
+					Bind(m("/tmp/hakurei.0/runtime/1"), m("/run/user/1971"), container.BindWritable).
+					Bind(m("/tmp/hakurei.0/tmpdir/1"), m("/tmp/"), container.BindWritable).
 					Place(m("/etc/passwd"), []byte("u0_a1:x:1971:100:Hakurei:/var/lib/persist/module/hakurei/0/1:/run/current-system/sw/bin/zsh\n")).
 					Place(m("/etc/group"), []byte("hakurei:x:100:\n")).
 					Bind(m("/run/user/1971/wayland-0"), m("/run/user/1971/wayland-0"), 0).
 					Bind(m("/run/user/1971/hakurei/8e2c76b066dabe574cf073bdb46eb5c1/pulse"), m("/run/user/1971/pulse/native"), 0).
 					Place(m(hst.Tmp+"/pulse-cookie"), nil).
-					Bind(m("/tmp/hakurei.1971/8e2c76b066dabe574cf073bdb46eb5c1/bus"), m("/run/user/1971/bus"), 0).
-					Bind(m("/tmp/hakurei.1971/8e2c76b066dabe574cf073bdb46eb5c1/system_bus_socket"), m("/run/dbus/system_bus_socket"), 0).
+					Bind(m("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/bus"), m("/run/user/1971/bus"), 0).
+					Bind(m("/tmp/hakurei.0/8e2c76b066dabe574cf073bdb46eb5c1/system_bus_socket"), m("/run/dbus/system_bus_socket"), 0).
 					Remount(m("/"), syscall.MS_RDONLY),
 				SeccompPresets: seccomp.PresetExt | seccomp.PresetDenyTTY | seccomp.PresetDenyDevel,
 				HostNet:        true,
@@ -378,7 +376,8 @@ func TestApp(t *testing.T) {
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Run("finalise", func(t *testing.T) {
-				sys, params, err := app.FinaliseIParams(t.Context(), tc.os, tc.config, &tc.id)
+				seal := outcome{syscallDispatcher: tc.k, id: &stringPair[state.ID]{tc.id, tc.id.String()}}
+				err := seal.finalise(t.Context(), tc.config)
 				if err != nil {
 					if s, ok := container.GetErrorMessage(err); !ok {
 						t.Fatalf("Seal: error = %v", err)
@@ -388,14 +387,14 @@ func TestApp(t *testing.T) {
 				}
 
 				t.Run("sys", func(t *testing.T) {
-					if !sys.Equal(tc.wantSys) {
-						t.Errorf("Seal: sys = %#v, want %#v", sys, tc.wantSys)
+					if !seal.sys.Equal(tc.wantSys) {
+						t.Errorf("Seal: sys = %#v, want %#v", seal.sys, tc.wantSys)
 					}
 				})
 
 				t.Run("params", func(t *testing.T) {
-					if !reflect.DeepEqual(params, tc.wantParams) {
-						t.Errorf("seal: params =\n%s\n, want\n%s", mustMarshal(params), mustMarshal(tc.wantParams))
+					if !reflect.DeepEqual(seal.container, tc.wantParams) {
+						t.Errorf("seal: container =\n%s\n, want\n%s", mustMarshal(seal.container), mustMarshal(tc.wantParams))
 					}
 				})
 			})
diff --git a/internal/app/container.go b/internal/app/container.go
index 26bda26..d406d21 100644
--- a/internal/app/container.go
+++ b/internal/app/container.go
@@ -11,7 +11,6 @@ import (
 	"hakurei.app/container"
 	"hakurei.app/container/seccomp"
 	"hakurei.app/hst"
-	"hakurei.app/internal/sys"
 	"hakurei.app/system/dbus"
 )
 
@@ -20,7 +19,13 @@ const preallocateOpsCount = 1 << 5
 
 // newContainer initialises [container.Params] via [hst.ContainerConfig].
 // Note that remaining container setup must be queued by the caller.
-func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid *int) (*container.Params, map[string]string, error) {
+func newContainer(
+	k syscallDispatcher,
+	s *hst.ContainerConfig,
+	prefix string,
+	sc *hst.Paths,
+	uid, gid *int,
+) (*container.Params, map[string]string, error) {
 	if s == nil {
 		return nil, nil, newWithMessage("invalid container configuration")
 	}
@@ -38,9 +43,7 @@ func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid
 		ForwardCancel: s.WaitDelay >= 0,
 	}
 
-	as := &hst.ApplyState{
-		AutoEtcPrefix: prefix,
-	}
+	as := &hst.ApplyState{AutoEtcPrefix: prefix}
 	{
 		ops := make(container.Ops, 0, preallocateOpsCount+len(s.Filesystem))
 		params.Ops = &ops
@@ -65,13 +68,13 @@ func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid
 	}
 
 	if s.MapRealUID {
-		params.Uid = os.Getuid()
+		params.Uid = k.getuid()
 		*uid = params.Uid
-		params.Gid = os.Getgid()
+		params.Gid = k.getgid()
 		*gid = params.Gid
 	} else {
-		*uid = container.OverflowUid()
-		*gid = container.OverflowGid()
+		*uid = k.overflowUid()
+		*gid = k.overflowGid()
 	}
 
 	filesystem := s.Filesystem
@@ -107,7 +110,6 @@ func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid
 	to warn about issues in custom configuration; it is NOT a security feature
 	and should not be treated as such, ALWAYS be careful with what you bind */
 	var hidePaths []string
-	sc := os.Paths()
 	hidePaths = append(hidePaths, sc.RuntimePath.String(), sc.SharePath.String())
 	_, systemBusAddr := dbus.Address()
 	if entries, err := dbus.Parse([]byte(systemBusAddr)); err != nil {
@@ -124,11 +126,11 @@ func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid
 						// get parent dir of socket
 						dir := path.Dir(pair[1])
 						if dir == "." || dir == container.FHSRoot {
-							os.Printf("dbus socket %q is in an unusual location", pair[1])
+							k.verbosef("dbus socket %q is in an unusual location", pair[1])
 						}
 						hidePaths = append(hidePaths, dir)
 					} else {
-						os.Printf("dbus socket %q is not absolute", pair[1])
+						k.verbosef("dbus socket %q is not absolute", pair[1])
 					}
 				}
 			}
@@ -136,7 +138,7 @@ func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid
 	}
 	hidePathMatch := make([]bool, len(hidePaths))
 	for i := range hidePaths {
-		if err := evalSymlinks(os, &hidePaths[i]); err != nil {
+		if err := evalSymlinks(k, &hidePaths[i]); err != nil {
 			return nil, nil, err
 		}
 	}
@@ -155,7 +157,7 @@ func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid
 	// AutoRootOp is a collection of many BindMountOp internally
 	var autoRootEntries []fs.DirEntry
 	if autoroot != nil {
-		if d, err := os.ReadDir(autoroot.Source.String()); err != nil {
+		if d, err := k.readdir(autoroot.Source.String()); err != nil {
 			return nil, nil, err
 		} else {
 			// autoroot counter
@@ -191,7 +193,7 @@ func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid
 		}
 
 		hidePathSourceEval[i] = [2]string{a.String(), a.String()}
-		if err := evalSymlinks(os, &hidePathSourceEval[i][0]); err != nil {
+		if err := evalSymlinks(k, &hidePathSourceEval[i][0]); err != nil {
 			return nil, nil, err
 		}
 	}
@@ -207,7 +209,7 @@ func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid
 				return nil, nil, err
 			} else if ok {
 				hidePathMatch[i] = true
-				os.Printf("hiding path %q from %q", hidePaths[i], p[1])
+				k.verbosef("hiding path %q from %q", hidePaths[i], p[1])
 			}
 		}
 	}
@@ -238,12 +240,13 @@ func newContainer(s *hst.ContainerConfig, os sys.State, prefix string, uid, gid
 	return params, maps.Clone(s.Env), nil
 }
 
-func evalSymlinks(os sys.State, v *string) error {
-	if p, err := os.EvalSymlinks(*v); err != nil {
+// evalSymlinks calls syscallDispatcher.evalSymlinks but discards errors unwrapping to [fs.ErrNotExist].
+func evalSymlinks(k syscallDispatcher, v *string) error {
+	if p, err := k.evalSymlinks(*v); err != nil {
 		if !errors.Is(err, fs.ErrNotExist) {
 			return err
 		}
-		os.Printf("path %q does not yet exist", *v)
+		k.verbosef("path %q does not yet exist", *v)
 	} else {
 		*v = p
 	}
diff --git a/internal/app/dispatcher.go b/internal/app/dispatcher.go
new file mode 100644
index 0000000..deecfa9
--- /dev/null
+++ b/internal/app/dispatcher.go
@@ -0,0 +1,99 @@
+package app
+
+import (
+	"log"
+	"os"
+	"os/exec"
+	"os/user"
+	"path/filepath"
+
+	"hakurei.app/container"
+	"hakurei.app/internal"
+	"hakurei.app/internal/hlog"
+)
+
+// syscallDispatcher provides methods that make state-dependent system calls as part of their behaviour.
+type syscallDispatcher interface {
+	// new starts a goroutine with a new instance of syscallDispatcher.
+	// A syscallDispatcher must never be used in any goroutine other than the one owning it,
+	// just synchronising access is not enough, as this is for test instrumentation.
+	new(f func(k syscallDispatcher))
+
+	// getuid provides [os.Getuid].
+	getuid() int
+	// getgid provides [os.Getgid].
+	getgid() int
+	// lookupEnv provides [os.LookupEnv].
+	lookupEnv(key string) (string, bool)
+	// stat provides [os.Stat].
+	stat(name string) (os.FileInfo, error)
+	// readdir provides [os.ReadDir].
+	readdir(name string) ([]os.DirEntry, error)
+	// tempdir provides [os.TempDir].
+	tempdir() string
+
+	// evalSymlinks provides [filepath.EvalSymlinks].
+	evalSymlinks(path string) (string, error)
+
+	// lookPath provides exec.LookPath.
+	lookPath(file string) (string, error)
+
+	// lookupGroupId calls [user.LookupGroup] and returns the Gid field of the resulting [user.Group] struct.
+	lookupGroupId(name string) (string, error)
+
+	// cmdOutput provides the Output method of [exec.Cmd].
+	cmdOutput(cmd *exec.Cmd) ([]byte, error)
+
+	// overflowUid provides [container.OverflowUid].
+	overflowUid() int
+	// overflowGid provides [container.OverflowGid].
+	overflowGid() int
+
+	// mustHsuPath provides [internal.MustHsuPath].
+	mustHsuPath() string
+
+	// fatalf provides [log.Fatalf].
+	fatalf(format string, v ...any)
+
+	isVerbose() bool
+	verbose(v ...any)
+	verbosef(format string, v ...any)
+}
+
+// direct implements syscallDispatcher on the current kernel.
+type direct struct{}
+
+func (k direct) new(f func(k syscallDispatcher)) { go f(k) }
+
+func (direct) getuid() int                                { return os.Getuid() }
+func (direct) getgid() int                                { return os.Getgid() }
+func (direct) lookupEnv(key string) (string, bool)        { return os.LookupEnv(key) }
+func (direct) stat(name string) (os.FileInfo, error)      { return os.Stat(name) }
+func (direct) readdir(name string) ([]os.DirEntry, error) { return os.ReadDir(name) }
+func (direct) tempdir() string                            { return os.TempDir() }
+
+func (direct) evalSymlinks(path string) (string, error) { return filepath.EvalSymlinks(path) }
+
+func (direct) lookPath(file string) (string, error) { return exec.LookPath(file) }
+
+func (direct) lookupGroupId(name string) (gid string, err error) {
+	var group *user.Group
+	group, err = user.LookupGroup(name)
+	if group != nil {
+		gid = group.Gid
+	}
+	return
+}
+
+func (direct) cmdOutput(cmd *exec.Cmd) ([]byte, error) { return cmd.Output() }
+
+func (direct) overflowUid() int { return container.OverflowUid() }
+func (direct) overflowGid() int { return container.OverflowGid() }
+
+func (direct) mustHsuPath() string { return internal.MustHsuPath() }
+
+func (direct) fatalf(format string, v ...any) { log.Fatalf(format, v...) }
+
+func (k direct) isVerbose() bool                { return hlog.Load() }
+func (direct) verbose(v ...any)                 { hlog.Verbose(v...) }
+func (direct) verbosef(format string, v ...any) { hlog.Verbosef(format, v...) }
diff --git a/internal/app/export_test.go b/internal/app/export_test.go
deleted file mode 100644
index 1bfba48..0000000
--- a/internal/app/export_test.go
+++ /dev/null
@@ -1,16 +0,0 @@
-package app
-
-import (
-	"context"
-
-	"hakurei.app/container"
-	"hakurei.app/hst"
-	"hakurei.app/internal/app/state"
-	"hakurei.app/internal/sys"
-	"hakurei.app/system"
-)
-
-func FinaliseIParams(ctx context.Context, k sys.State, config *hst.Config, id *state.ID) (*system.I, *container.Params, error) {
-	seal := outcome{id: &stringPair[state.ID]{*id, id.String()}}
-	return seal.sys, seal.container, seal.finalise(ctx, k, config)
-}
diff --git a/internal/app/seal.go b/internal/app/finalise.go
similarity index 73%
rename from internal/app/seal.go
rename to internal/app/finalise.go
index c7dd9d6..2a0e5e6 100644
--- a/internal/app/seal.go
+++ b/internal/app/finalise.go
@@ -21,7 +21,6 @@ import (
 	"hakurei.app/hst"
 	"hakurei.app/internal/app/state"
 	"hakurei.app/internal/hlog"
-	"hakurei.app/internal/sys"
 	"hakurei.app/system"
 	"hakurei.app/system/acl"
 	"hakurei.app/system/dbus"
@@ -54,8 +53,9 @@ type outcome struct {
 	container *container.Params
 	env       map[string]string
 	sync      *os.File
+	active    atomic.Bool
 
-	f atomic.Bool
+	syscallDispatcher
 }
 
 // shareHost holds optional share directory state that must not be accessed directly
@@ -120,7 +120,7 @@ type hsuUser struct {
 	username string
 }
 
-func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Config) error {
+func (k *outcome) finalise(ctx context.Context, config *hst.Config) error {
 	const (
 		home  = "HOME"
 		shell = "SHELL"
@@ -144,14 +144,13 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 		// unreachable
 		panic("invalid call to finalise")
 	}
-	if seal.ctx != nil {
+	if k.ctx != nil {
 		// unreachable
 		panic("attempting to finalise twice")
 	}
-	seal.ctx = ctx
+	k.ctx = ctx
 
 	if config == nil {
-		// unreachable
 		return newWithMessage("invalid configuration")
 	}
 	if config.Home == nil {
@@ -164,7 +163,7 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 		if err := gob.NewEncoder(ct).Encode(config); err != nil {
 			return &hst.AppError{Step: "encode initial config", Err: err}
 		}
-		seal.ct = ct
+		k.ct = ct
 	}
 
 	// allowed identity range 0 to 9999, this is checked again in hsu
@@ -172,22 +171,23 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 		return newWithMessage(fmt.Sprintf("identity %d out of range", config.Identity))
 	}
 
-	seal.user = hsuUser{
+	k.user = hsuUser{
 		identity: newInt(config.Identity),
 		home:     config.Home,
 		username: config.Username,
 	}
 
-	if seal.user.username == "" {
-		seal.user.username = "chronos"
-	} else if !isValidUsername(seal.user.username) {
-		return newWithMessage(fmt.Sprintf("invalid user name %q", seal.user.username))
+	hsu := Hsu{k: k}
+	if k.user.username == "" {
+		k.user.username = "chronos"
+	} else if !isValidUsername(k.user.username) {
+		return newWithMessage(fmt.Sprintf("invalid user name %q", k.user.username))
 	}
-	seal.user.uid = newInt(sys.MustUid(k, seal.user.identity.unwrap()))
+	k.user.uid = newInt(HsuUid(hsu.MustID(), k.user.identity.unwrap()))
 
-	seal.user.supp = make([]string, len(config.Groups))
+	k.user.supp = make([]string, len(config.Groups))
 	for i, name := range config.Groups {
-		if g, err := k.LookupGroup(name); err != nil {
+		if gid, err := k.lookupGroupId(name); err != nil {
 			var unknownGroupError user.UnknownGroupError
 			if errors.As(err, &unknownGroupError) {
 				return newWithMessageError(fmt.Sprintf("unknown group %q", name), unknownGroupError)
@@ -195,7 +195,7 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 				return &hst.AppError{Step: "look up group by name", Err: err}
 			}
 		} else {
-			seal.user.supp[i] = g.Gid
+			k.user.supp[i] = gid
 		}
 	}
 
@@ -205,7 +205,7 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 
 		if config.Shell == nil {
 			config.Shell = container.AbsFHSRoot.Append("bin", "sh")
-			s, _ := k.LookupEnv(shell)
+			s, _ := k.lookupEnv(shell)
 			if a, err := container.NewAbs(s); err == nil {
 				config.Shell = a
 			}
@@ -214,7 +214,7 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 		// hsu clears the environment so resolve paths early
 		if config.Path == nil {
 			if len(config.Args) > 0 {
-				if p, err := k.LookPath(config.Args[0]); err != nil {
+				if p, err := k.lookPath(config.Args[0]); err != nil {
 					return &hst.AppError{Step: "look up executable file", Err: err}
 				} else if config.Path, err = container.NewAbs(p); err != nil {
 					return newWithMessageError(err.Error(), err)
@@ -250,7 +250,7 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 
 		// hide nscd from container if present
 		nscd := container.AbsFHSVar.Append("run/nscd")
-		if _, err := k.Stat(nscd.String()); !errors.Is(err, fs.ErrNotExist) {
+		if _, err := k.stat(nscd.String()); !errors.Is(err, fs.ErrNotExist) {
 			conf.Filesystem = append(conf.Filesystem, hst.FilesystemConfigJSON{FilesystemConfig: &hst.FSEphemeral{Target: nscd}})
 		}
 
@@ -274,86 +274,89 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 		return newWithMessage("invalid program path")
 	}
 
+	// TODO(ophestra): revert this after params to shim
+	share := &shareHost{seal: k}
+	copyPaths(k.syscallDispatcher, &share.sc, hsu.MustID())
+
 	var mapuid, mapgid *stringPair[int]
 	{
 		var uid, gid int
 		var err error
-		seal.container, seal.env, err = newContainer(config.Container, k, seal.id.String(), &uid, &gid)
-		seal.waitDelay = config.Container.WaitDelay
+		k.container, k.env, err = newContainer(k, config.Container, k.id.String(), &share.sc, &uid, &gid)
+		k.waitDelay = config.Container.WaitDelay
 		if err != nil {
 			return &hst.AppError{Step: "initialise container configuration", Err: err}
 		}
 		if len(config.Args) == 0 {
 			config.Args = []string{config.Path.String()}
 		}
-		seal.container.Path = config.Path
-		seal.container.Args = config.Args
+		k.container.Path = config.Path
+		k.container.Args = config.Args
 
 		mapuid = newInt(uid)
 		mapgid = newInt(gid)
-		if seal.env == nil {
-			seal.env = make(map[string]string, 1<<6)
+		if k.env == nil {
+			k.env = make(map[string]string, 1<<6)
 		}
 	}
 
 	// inner XDG_RUNTIME_DIR default formatting of `/run/user/%d` as mapped uid
 	innerRuntimeDir := container.AbsFHSRunUser.Append(mapuid.String())
-	seal.env[xdgRuntimeDir] = innerRuntimeDir.String()
-	seal.env[xdgSessionClass] = "user"
-	seal.env[xdgSessionType] = "tty"
+	k.env[xdgRuntimeDir] = innerRuntimeDir.String()
+	k.env[xdgSessionClass] = "user"
+	k.env[xdgSessionType] = "tty"
 
-	share := &shareHost{seal: seal, sc: k.Paths()}
-	seal.runDirPath = share.sc.RunDirPath
-	seal.sys = system.New(seal.ctx, seal.user.uid.unwrap())
-	seal.sys.Ensure(share.sc.SharePath.String(), 0711)
+	k.runDirPath = share.sc.RunDirPath
+	k.sys = system.New(k.ctx, k.user.uid.unwrap())
+	k.sys.Ensure(share.sc.SharePath.String(), 0711)
 
 	{
 		runtimeDir := share.sc.SharePath.Append("runtime")
-		seal.sys.Ensure(runtimeDir.String(), 0700)
-		seal.sys.UpdatePermType(system.User, runtimeDir.String(), acl.Execute)
-		runtimeDirInst := runtimeDir.Append(seal.user.identity.String())
-		seal.sys.Ensure(runtimeDirInst.String(), 0700)
-		seal.sys.UpdatePermType(system.User, runtimeDirInst.String(), acl.Read, acl.Write, acl.Execute)
-		seal.container.Tmpfs(container.AbsFHSRunUser, 1<<12, 0755)
-		seal.container.Bind(runtimeDirInst, innerRuntimeDir, container.BindWritable)
+		k.sys.Ensure(runtimeDir.String(), 0700)
+		k.sys.UpdatePermType(system.User, runtimeDir.String(), acl.Execute)
+		runtimeDirInst := runtimeDir.Append(k.user.identity.String())
+		k.sys.Ensure(runtimeDirInst.String(), 0700)
+		k.sys.UpdatePermType(system.User, runtimeDirInst.String(), acl.Read, acl.Write, acl.Execute)
+		k.container.Tmpfs(container.AbsFHSRunUser, 1<<12, 0755)
+		k.container.Bind(runtimeDirInst, innerRuntimeDir, container.BindWritable)
 	}
 
 	{
 		tmpdir := share.sc.SharePath.Append("tmpdir")
-		seal.sys.Ensure(tmpdir.String(), 0700)
-		seal.sys.UpdatePermType(system.User, tmpdir.String(), acl.Execute)
-		tmpdirInst := tmpdir.Append(seal.user.identity.String())
-		seal.sys.Ensure(tmpdirInst.String(), 01700)
-		seal.sys.UpdatePermType(system.User, tmpdirInst.String(), acl.Read, acl.Write, acl.Execute)
+		k.sys.Ensure(tmpdir.String(), 0700)
+		k.sys.UpdatePermType(system.User, tmpdir.String(), acl.Execute)
+		tmpdirInst := tmpdir.Append(k.user.identity.String())
+		k.sys.Ensure(tmpdirInst.String(), 01700)
+		k.sys.UpdatePermType(system.User, tmpdirInst.String(), acl.Read, acl.Write, acl.Execute)
 		// mount inner /tmp from share so it shares persistence and storage behaviour of host /tmp
-		seal.container.Bind(tmpdirInst, container.AbsFHSTmp, container.BindWritable)
+		k.container.Bind(tmpdirInst, container.AbsFHSTmp, container.BindWritable)
 	}
 
 	{
 		username := "chronos"
-		if seal.user.username != "" {
-			username = seal.user.username
+		if k.user.username != "" {
+			username = k.user.username
 		}
-		seal.container.Dir = seal.user.home
-		seal.env["HOME"] = seal.user.home.String()
-		seal.env["USER"] = username
-		seal.env[shell] = config.Shell.String()
+		k.container.Dir = k.user.home
+		k.env["HOME"] = k.user.home.String()
+		k.env["USER"] = username
+		k.env[shell] = config.Shell.String()
 
-		seal.container.Place(container.AbsFHSEtc.Append("passwd"),
-			[]byte(username+":x:"+mapuid.String()+":"+mapgid.String()+":Hakurei:"+seal.user.home.String()+":"+config.Shell.String()+"\n"))
-		seal.container.Place(container.AbsFHSEtc.Append("group"),
+		k.container.Place(container.AbsFHSEtc.Append("passwd"),
+			[]byte(username+":x:"+mapuid.String()+":"+mapgid.String()+":Hakurei:"+k.user.home.String()+":"+config.Shell.String()+"\n"))
+		k.container.Place(container.AbsFHSEtc.Append("group"),
 			[]byte("hakurei:x:"+mapgid.String()+":\n"))
 	}
 
 	// pass TERM for proper terminal I/O in initial process
-	if t, ok := k.LookupEnv(term); ok {
-		seal.env[term] = t
+	if t, ok := k.lookupEnv(term); ok {
+		k.env[term] = t
 	}
 
 	if config.Enablements.Unwrap()&system.EWayland != 0 {
 		// outer wayland socket (usually `/run/user/%d/wayland-%d`)
 		var socketPath *container.Absolute
-		if name, ok := k.LookupEnv(wayland.WaylandDisplay); !ok {
+		if name, ok := k.lookupEnv(wayland.WaylandDisplay); !ok {
 			hlog.Verbose(wayland.WaylandDisplay + " is not set, assuming " + wayland.FallbackName)
 			socketPath = share.sc.RuntimePath.Append(wayland.FallbackName)
 		} else if a, err := container.NewAbs(name); err != nil {
@@ -363,28 +366,28 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 		}
 
 		innerPath := innerRuntimeDir.Append(wayland.FallbackName)
-		seal.env[wayland.WaylandDisplay] = wayland.FallbackName
+		k.env[wayland.WaylandDisplay] = wayland.FallbackName
 
 		if !config.DirectWayland { // set up security-context-v1
 			appID := config.ID
 			if appID == "" {
 				// use instance ID in case app id is not set
-				appID = "app.hakurei." + seal.id.String()
+				appID = "app.hakurei." + k.id.String()
 			}
 			// downstream socket paths
 			outerPath := share.instance().Append("wayland")
-			seal.sys.Wayland(&seal.sync, outerPath.String(), socketPath.String(), appID, seal.id.String())
-			seal.container.Bind(outerPath, innerPath, 0)
+			k.sys.Wayland(&k.sync, outerPath.String(), socketPath.String(), appID, k.id.String())
+			k.container.Bind(outerPath, innerPath, 0)
 		} else { // bind mount wayland socket (insecure)
 			hlog.Verbose("direct wayland access, PROCEED WITH CAUTION")
 			share.ensureRuntimeDir()
-			seal.container.Bind(socketPath, innerPath, 0)
-			seal.sys.UpdatePermType(system.EWayland, socketPath.String(), acl.Read, acl.Write, acl.Execute)
+			k.container.Bind(socketPath, innerPath, 0)
+			k.sys.UpdatePermType(system.EWayland, socketPath.String(), acl.Read, acl.Write, acl.Execute)
 		}
 	}
 
 	if config.Enablements.Unwrap()&system.EX11 != 0 {
-		if d, ok := k.LookupEnv(display); !ok {
+		if d, ok := k.lookupEnv(display); !ok {
 			return newWithMessage("DISPLAY is not set")
 		} else {
 			socketDir := container.AbsFHSTmp.Append(".X11-unix")
@@ -402,21 +405,21 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 				}
 			}
 			if socketPath != nil {
-				if _, err := k.Stat(socketPath.String()); err != nil {
+				if _, err := k.stat(socketPath.String()); err != nil {
 					if !errors.Is(err, fs.ErrNotExist) {
 						return &hst.AppError{Step: fmt.Sprintf("access X11 socket %q", socketPath), Err: err}
 					}
 				} else {
-					seal.sys.UpdatePermType(system.EX11, socketPath.String(), acl.Read, acl.Write, acl.Execute)
+					k.sys.UpdatePermType(system.EX11, socketPath.String(), acl.Read, acl.Write, acl.Execute)
 					if !config.Container.HostAbstract {
 						d = "unix:" + socketPath.String()
 					}
 				}
 			}
 
-			seal.sys.ChangeHosts("#" + seal.user.uid.String())
-			seal.env[display] = d
-			seal.container.Bind(socketDir, socketDir, 0)
+			k.sys.ChangeHosts("#" + k.user.uid.String())
+			k.env[display] = d
+			k.container.Bind(socketDir, socketDir, 0)
 		}
 	}
 
@@ -426,14 +429,14 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 		// PulseAudio socket (usually `/run/user/%d/pulse/native`)
 		pulseSocket := pulseRuntimeDir.Append("native")
 
-		if _, err := k.Stat(pulseRuntimeDir.String()); err != nil {
+		if _, err := k.stat(pulseRuntimeDir.String()); err != nil {
 			if !errors.Is(err, fs.ErrNotExist) {
 				return &hst.AppError{Step: fmt.Sprintf("access PulseAudio directory %q", pulseRuntimeDir), Err: err}
 			}
 			return newWithMessage(fmt.Sprintf("PulseAudio directory %q not found", pulseRuntimeDir))
 		}
 
-		if s, err := k.Stat(pulseSocket.String()); err != nil {
+		if s, err := k.stat(pulseSocket.String()); err != nil {
 			if !errors.Is(err, fs.ErrNotExist) {
 				return &hst.AppError{Step: fmt.Sprintf("access PulseAudio socket %q", pulseSocket), Err: err}
 			}
@@ -447,9 +450,9 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 		// hard link pulse socket into target-executable share
 		innerPulseRuntimeDir := share.runtime().Append("pulse")
 		innerPulseSocket := innerRuntimeDir.Append("pulse", "native")
-		seal.sys.Link(pulseSocket.String(), innerPulseRuntimeDir.String())
-		seal.container.Bind(innerPulseRuntimeDir, innerPulseSocket, 0)
-		seal.env[pulseServer] = "unix:" + innerPulseSocket.String()
+		k.sys.Link(pulseSocket.String(), innerPulseRuntimeDir.String())
+		k.container.Bind(innerPulseRuntimeDir, innerPulseSocket, 0)
+		k.env[pulseServer] = "unix:" + innerPulseSocket.String()
 
 		// publish current user's pulse cookie for target user
 		var paCookiePath *container.Absolute
@@ -457,7 +460,7 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 			const paLocateStep = "locate PulseAudio cookie"
 
 			// from environment
-			if p, ok := k.LookupEnv(pulseCookie); ok {
+			if p, ok := k.lookupEnv(pulseCookie); ok {
 				if a, err := container.NewAbs(p); err != nil {
 					return &hst.AppError{Step: paLocateStep, Err: err}
 				} else {
@@ -468,14 +471,14 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 			}
 
 			// $HOME/.pulse-cookie
-			if p, ok := k.LookupEnv(home); ok {
+			if p, ok := k.lookupEnv(home); ok {
 				if a, err := container.NewAbs(p); err != nil {
 					return &hst.AppError{Step: paLocateStep, Err: err}
 				} else {
 					paCookiePath = a.Append(".pulse-cookie")
 				}
 
-				if s, err := k.Stat(paCookiePath.String()); err != nil {
+				if s, err := k.stat(paCookiePath.String()); err != nil {
 					paCookiePath = nil
 					if !errors.Is(err, fs.ErrNotExist) {
 						return &hst.AppError{Step: "access PulseAudio cookie", Err: err}
@@ -489,13 +492,13 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 			}
 
 			// $XDG_CONFIG_HOME/pulse/cookie
-			if p, ok := k.LookupEnv(xdgConfigHome); ok {
+			if p, ok := k.lookupEnv(xdgConfigHome); ok {
 				if a, err := container.NewAbs(p); err != nil {
 					return &hst.AppError{Step: paLocateStep, Err: err}
 				} else {
 					paCookiePath = a.Append("pulse", "cookie")
 				}
-				if s, err := k.Stat(paCookiePath.String()); err != nil {
+				if s, err := k.stat(paCookiePath.String()); err != nil {
 					paCookiePath = nil
 					if !errors.Is(err, fs.ErrNotExist) {
 						return &hst.AppError{Step: "access PulseAudio cookie", Err: err}
@@ -512,10 +515,10 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 
 		if paCookiePath != nil {
 			innerDst := hst.AbsTmp.Append("/pulse-cookie")
-			seal.env[pulseCookie] = innerDst.String()
+			k.env[pulseCookie] = innerDst.String()
 			var payload *[]byte
-			seal.container.PlaceP(innerDst, &payload)
-			seal.sys.CopyFile(payload, paCookiePath.String(), 256, 256)
+			k.container.PlaceP(innerDst, &payload)
+			k.sys.CopyFile(payload, paCookiePath.String(), 256, 256)
 		} else {
 			hlog.Verbose("cannot locate PulseAudio cookie (tried " +
 				"$PULSE_COOKIE, " +
@@ -534,30 +537,30 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 		sessionPath, systemPath := share.instance().Append("bus"), share.instance().Append("system_bus_socket")
 
 		// configure dbus proxy
-		if f, err := seal.sys.ProxyDBus(
+		if f, err := k.sys.ProxyDBus(
 			config.SessionBus, config.SystemBus,
 			sessionPath.String(), systemPath.String(),
 		); err != nil {
 			return err
 		} else {
-			seal.dbusMsg = f
+			k.dbusMsg = f
 		}
 
 		// share proxy sockets
 		sessionInner := innerRuntimeDir.Append("bus")
-		seal.env[dbusSessionBusAddress] = "unix:path=" + sessionInner.String()
-		seal.container.Bind(sessionPath, sessionInner, 0)
-		seal.sys.UpdatePerm(sessionPath.String(), acl.Read, acl.Write)
+		k.env[dbusSessionBusAddress] = "unix:path=" + sessionInner.String()
+		k.container.Bind(sessionPath, sessionInner, 0)
+		k.sys.UpdatePerm(sessionPath.String(), acl.Read, acl.Write)
 		if config.SystemBus != nil {
 			systemInner := container.AbsFHSRun.Append("dbus/system_bus_socket")
-			seal.env[dbusSystemBusAddress] = "unix:path=" + systemInner.String()
-			seal.container.Bind(systemPath, systemInner, 0)
-			seal.sys.UpdatePerm(systemPath.String(), acl.Read, acl.Write)
+			k.env[dbusSystemBusAddress] = "unix:path=" + systemInner.String()
+			k.container.Bind(systemPath, systemInner, 0)
+			k.sys.UpdatePerm(systemPath.String(), acl.Read, acl.Write)
 		}
 	}
 
 	// mount root read-only as the final setup Op
-	seal.container.Remount(container.AbsFHSRoot, syscall.MS_RDONLY)
+	k.container.Remount(container.AbsFHSRoot, syscall.MS_RDONLY)
 
 	// append ExtraPerms last
 	for _, p := range config.ExtraPerms {
@@ -566,7 +569,7 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 		}
 
 		if p.Ensure {
-			seal.sys.Ensure(p.Path.String(), 0700)
+			k.sys.Ensure(p.Path.String(), 0700)
 		}
 
 		perms := make(acl.Perms, 0, 3)
@@ -579,23 +582,23 @@ func (seal *outcome) finalise(ctx context.Context, k sys.State, config *hst.Conf
 		if p.Execute {
 			perms = append(perms, acl.Execute)
 		}
-		seal.sys.UpdatePermType(system.User, p.Path.String(), perms...)
+		k.sys.UpdatePermType(system.User, p.Path.String(), perms...)
 	}
 
 	// flatten and sort env for deterministic behaviour
-	seal.container.Env = make([]string, 0, len(seal.env))
-	for k, v := range seal.env {
-		if strings.IndexByte(k, '=') != -1 {
+	k.container.Env = make([]string, 0, len(k.env))
+	for key, value := range k.env {
+		if strings.IndexByte(key, '=') != -1 {
 			return &hst.AppError{Step: "flatten environment", Err: syscall.EINVAL,
-				Msg: fmt.Sprintf("invalid environment variable %s", k)}
+				Msg: fmt.Sprintf("invalid environment variable %s", key)}
 		}
-		seal.container.Env = append(seal.container.Env, k+"="+v)
+		k.container.Env = append(k.container.Env, key+"="+value)
 	}
-	slices.Sort(seal.container.Env)
+	slices.Sort(k.container.Env)
 
 	if hlog.Load() {
 		hlog.Verbosef("created application seal for uid %s (%s) groups: %v, argv: %s, ops: %d",
-			seal.user.uid, seal.user.username, config.Groups, seal.container.Args, len(*seal.container.Ops))
+			k.user.uid, k.user.username, config.Groups, k.container.Args, len(*k.container.Ops))
 	}
 
 	return nil
diff --git a/internal/sys/hsu.go b/internal/app/hsu.go
similarity index 70%
rename from internal/sys/hsu.go
rename to internal/app/hsu.go
index 5ae1204..0078ef0 100644
--- a/internal/sys/hsu.go
+++ b/internal/app/hsu.go
@@ -1,4 +1,4 @@
-package sys
+package app
 
 import (
 	"errors"
@@ -11,7 +11,6 @@ import (
 
 	"hakurei.app/container"
 	"hakurei.app/hst"
-	"hakurei.app/internal"
 	"hakurei.app/internal/hlog"
 )
 
@@ -20,15 +19,28 @@ type Hsu struct {
 	idOnce sync.Once
 	idErr  error
 	id     int
+
+	kOnce sync.Once
+	k     syscallDispatcher
 }
 
 var ErrHsuAccess = errors.New("current user is not in the hsurc file")
 
+// ensureDispatcher ensures Hsu.k is not nil.
+func (h *Hsu) ensureDispatcher() {
+	h.kOnce.Do(func() {
+		if h.k == nil {
+			h.k = direct{}
+		}
+	})
+}
+
 // ID returns the current user hsurc identifier. ErrHsuAccess is returned if the current user is not in hsurc.
 func (h *Hsu) ID() (int, error) {
+	h.ensureDispatcher()
 	h.idOnce.Do(func() {
 		h.id = -1
-		hsuPath := internal.MustHsuPath()
+		hsuPath := h.k.mustHsuPath()
 
 		cmd := exec.Command(hsuPath)
 		cmd.Path = hsuPath
@@ -41,7 +53,7 @@ func (h *Hsu) ID() (int, error) {
 		)
 
 		const step = "obtain uid from hsu"
-		if p, h.idErr = cmd.Output(); h.idErr == nil {
+		if p, h.idErr = h.k.cmdOutput(cmd); h.idErr == nil {
 			h.id, h.idErr = strconv.Atoi(string(p))
 			if h.idErr != nil {
 				h.idErr = &hst.AppError{Step: step, Err: h.idErr, Msg: "invalid uid string from hsu"}
@@ -58,22 +70,14 @@ func (h *Hsu) ID() (int, error) {
 	return h.id, h.idErr
 }
 
-func (h *Hsu) Uid(identity int) (int, error) {
+// MustID calls [Hsu.ID] and terminates on error.
+func (h *Hsu) MustID() int {
 	id, err := h.ID()
 	if err == nil {
-		return 1000000 + id*10000 + identity, nil
-	}
-	return id, err
-}
-
-// MustUid calls [State.Uid] and terminates on error.
-func MustUid(s State, identity int) int {
-	uid, err := s.Uid(identity)
-	if err == nil {
-		return uid
+		return id
 	}
 
-	const fallback = "cannot obtain uid from setuid wrapper:"
+	const fallback = "cannot retrieve user id from setuid wrapper:"
 	if errors.Is(err, ErrHsuAccess) {
 		hlog.Verbose("*"+fallback, err)
 		os.Exit(1)
@@ -86,3 +90,7 @@ func MustUid(s State, identity int) int {
 		return -0xdeadbeef
 	}
 }
+
+// HsuUid returns target uid for the stable hsu uid format.
+// No bounds check is performed, a value retrieved from hsu is expected.
+func HsuUid(id, identity int) int { return 1000000 + id*10000 + identity }
diff --git a/internal/app/paths.go b/internal/app/paths.go
new file mode 100644
index 0000000..3316a22
--- /dev/null
+++ b/internal/app/paths.go
@@ -0,0 +1,36 @@
+package app
+
+import (
+	"strconv"
+
+	"hakurei.app/container"
+	"hakurei.app/hst"
+)
+
+// CopyPaths populates a [hst.Paths] struct.
+func CopyPaths(v *hst.Paths, userid int) { copyPaths(direct{}, v, userid) }
+
+// copyPaths populates a [hst.Paths] struct.
+func copyPaths(k syscallDispatcher, v *hst.Paths, userid int) {
+	const xdgRuntimeDir = "XDG_RUNTIME_DIR"
+
+	if tempDir, err := container.NewAbs(k.tempdir()); err != nil {
+		k.fatalf("invalid TMPDIR: %v", err)
+	} else {
+		v.TempDir = tempDir
+	}
+
+	v.SharePath = v.TempDir.Append("hakurei." + strconv.Itoa(userid))
+	k.verbosef("process share directory at %q", v.SharePath)
+
+	r, _ := k.lookupEnv(xdgRuntimeDir)
+	if a, err := container.NewAbs(r); err != nil {
+		// fall back to path in share since hakurei has no hard XDG dependency
+		v.RunDirPath = v.SharePath.Append("run")
+		v.RuntimePath = v.RunDirPath.Append("compat")
+	} else {
+		v.RuntimePath = a
+		v.RunDirPath = v.RuntimePath.Append("hakurei")
+	}
+	k.verbosef("runtime directory at %q", v.RunDirPath)
+}
diff --git a/internal/app/process.go b/internal/app/process.go
index 368b655..8ac0585 100644
--- a/internal/app/process.go
+++ b/internal/app/process.go
@@ -33,12 +33,12 @@ type mainState struct {
 	// Time is nil if no process was ever created.
 	Time *time.Time
 
-	seal    *outcome
 	store   state.Store
 	cancel  context.CancelFunc
 	cmd     *exec.Cmd
 	cmdWait chan error
 
+	k *outcome
 	uintptr
 }
 
@@ -79,13 +79,13 @@ func (ms mainState) beforeExit(isFault bool) {
 		waitDone := make(chan struct{})
 		// TODO(ophestra): enforce this limit early so it does not have to be done twice
 		shimTimeoutCompensated := shimWaitTimeout
-		if ms.seal.waitDelay > MaxShimWaitDelay {
+		if ms.k.waitDelay > MaxShimWaitDelay {
 			shimTimeoutCompensated += MaxShimWaitDelay
 		} else {
-			shimTimeoutCompensated += ms.seal.waitDelay
+			shimTimeoutCompensated += ms.k.waitDelay
 		}
 		// this ties waitDone to ctx with the additional compensated timeout duration
-		go func() { <-ms.seal.ctx.Done(); time.Sleep(shimTimeoutCompensated); close(waitDone) }()
+		go func() { <-ms.k.ctx.Done(); time.Sleep(shimTimeoutCompensated); close(waitDone) }()
 
 		select {
 		case err := <-ms.cmdWait:
@@ -128,20 +128,20 @@ func (ms mainState) beforeExit(isFault bool) {
 		}
 
 		hlog.Resume()
-		if ms.seal.sync != nil {
-			if err := ms.seal.sync.Close(); err != nil {
+		if ms.k.sync != nil {
+			if err := ms.k.sync.Close(); err != nil {
 				perror(err, "close wayland security context")
 			}
 		}
-		if ms.seal.dbusMsg != nil {
-			ms.seal.dbusMsg()
+		if ms.k.dbusMsg != nil {
+			ms.k.dbusMsg()
 		}
 	}
 
 	if ms.uintptr&mainNeedsRevert != 0 {
-		if ok, err := ms.store.Do(ms.seal.user.identity.unwrap(), func(c state.Cursor) {
+		if ok, err := ms.store.Do(ms.k.user.identity.unwrap(), func(c state.Cursor) {
 			if ms.uintptr&mainNeedsDestroy != 0 {
-				if err := c.Destroy(ms.seal.id.unwrap()); err != nil {
+				if err := c.Destroy(ms.k.id.unwrap()); err != nil {
 					perror(err, "destroy state entry")
 				}
 			}
@@ -151,7 +151,7 @@ func (ms mainState) beforeExit(isFault bool) {
 				// it is impossible to continue from this point;
 				// revert per-process state here to limit damage
 				ec := system.Process
-				if revertErr := ms.seal.sys.Revert((*system.Criteria)(&ec)); revertErr != nil {
+				if revertErr := ms.k.sys.Revert((*system.Criteria)(&ec)); revertErr != nil {
 					var joinError interface {
 						Unwrap() []error
 						error
@@ -189,7 +189,7 @@ func (ms mainState) beforeExit(isFault bool) {
 					}
 				}
 
-				if err = ms.seal.sys.Revert((*system.Criteria)(&ec)); err != nil {
+				if err = ms.k.sys.Revert((*system.Criteria)(&ec)); err != nil {
 					perror(err, "revert system setup")
 				}
 			}
@@ -219,8 +219,8 @@ func (ms mainState) fatal(fallback string, ferr error) {
 }
 
 // main carries out outcome and terminates. main does not return.
-func (seal *outcome) main() {
-	if !seal.f.CompareAndSwap(false, true) {
+func (k *outcome) main() {
+	if !k.active.CompareAndSwap(false, true) {
 		panic("outcome: attempted to run twice")
 	}
 
@@ -228,15 +228,15 @@ func (seal *outcome) main() {
 	hsuPath := internal.MustHsuPath()
 
 	// ms.beforeExit required beyond this point
-	ms := &mainState{seal: seal}
+	ms := &mainState{k: k}
 
-	if err := seal.sys.Commit(); err != nil {
+	if err := k.sys.Commit(); err != nil {
 		ms.fatal("cannot commit system setup:", err)
 	}
 	ms.uintptr |= mainNeedsRevert
-	ms.store = state.NewMulti(seal.runDirPath.String())
+	ms.store = state.NewMulti(k.runDirPath.String())
 
-	ctx, cancel := context.WithCancel(seal.ctx)
+	ctx, cancel := context.WithCancel(k.ctx)
 	defer cancel()
 	ms.cancel = cancel
 
@@ -255,14 +255,14 @@ func (seal *outcome) main() {
 			// passed through to shim by hsu
 			shimEnv + "=" + strconv.Itoa(fd),
 			// interpreted by hsu
-			"HAKUREI_IDENTITY=" + seal.user.identity.String(),
+			"HAKUREI_IDENTITY=" + k.user.identity.String(),
 		}
 	}
 
-	if len(seal.user.supp) > 0 {
-		hlog.Verbosef("attaching supplementary group ids %s", seal.user.supp)
+	if len(k.user.supp) > 0 {
+		hlog.Verbosef("attaching supplementary group ids %s", k.user.supp)
 		// interpreted by hsu
-		ms.cmd.Env = append(ms.cmd.Env, "HAKUREI_GROUPS="+strings.Join(seal.user.supp, " "))
+		ms.cmd.Env = append(ms.cmd.Env, "HAKUREI_GROUPS="+strings.Join(k.user.supp, " "))
 	}
 
 	hlog.Verbosef("setuid helper at %s", hsuPath)
@@ -284,8 +284,8 @@ func (seal *outcome) main() {
 		go func() {
 			setupErr <- e.Encode(&shimParams{
 				os.Getpid(),
-				seal.waitDelay,
-				seal.container,
+				k.waitDelay,
+				k.container,
 				hlog.Load(),
 			})
 		}()
@@ -302,12 +302,12 @@ func (seal *outcome) main() {
 	}
 
 	// shim accepted setup payload, create process state
-	if ok, err := ms.store.Do(seal.user.identity.unwrap(), func(c state.Cursor) {
+	if ok, err := ms.store.Do(k.user.identity.unwrap(), func(c state.Cursor) {
 		if err := c.Save(&state.State{
-			ID:   seal.id.unwrap(),
+			ID:   k.id.unwrap(),
 			PID:  ms.cmd.Process.Pid,
 			Time: *ms.Time,
-		}, seal.ct); err != nil {
+		}, k.ct); err != nil {
 			ms.fatal("cannot save state entry:", err)
 		}
 	}); err != nil {
diff --git a/internal/sys/interface.go b/internal/sys/interface.go
deleted file mode 100644
index f2465e6..0000000
--- a/internal/sys/interface.go
+++ /dev/null
@@ -1,76 +0,0 @@
-// Package sys wraps OS interaction library functions.
-package sys
-
-import (
-	"io/fs"
-	"log"
-	"os/user"
-	"strconv"
-
-	"hakurei.app/container"
-	"hakurei.app/hst"
-	"hakurei.app/internal/hlog"
-)
-
-// State provides safe interaction with operating system state.
-type State interface {
-	// Getuid provides [os.Getuid].
-	Getuid() int
-	// Getgid provides [os.Getgid].
-	Getgid() int
-	// LookupEnv provides [os.LookupEnv].
-	LookupEnv(key string) (string, bool)
-	// TempDir provides [os.TempDir].
-	TempDir() string
-	// LookPath provides exec.LookPath.
-	LookPath(file string) (string, error)
-	// MustExecutable provides [container.MustExecutable].
-	MustExecutable() string
-	// LookupGroup provides [user.LookupGroup].
-	LookupGroup(name string) (*user.Group, error)
-	// ReadDir provides [os.ReadDir].
-	ReadDir(name string) ([]fs.DirEntry, error)
-	// Stat provides [os.Stat].
-	Stat(name string) (fs.FileInfo, error)
-	// Open provides [os.Open].
-	Open(name string) (fs.File, error)
-	// EvalSymlinks provides filepath.EvalSymlinks.
-	EvalSymlinks(path string) (string, error)
-	// Exit provides [os.Exit].
-	Exit(code int)
-
-	Println(v ...any)
-	Printf(format string, v ...any)
-
-	// Paths returns a populated [hst.Paths] struct.
-	Paths() hst.Paths
-	// Uid invokes hsu and returns target uid.
-	// Any errors returned by Uid is already wrapped [hlog.BaseError].
-	Uid(identity int) (int, error)
-}
-
-// MustGetUserID obtains user id from hsu by querying uid of identity 0.
-func MustGetUserID(os State) int { return (MustUid(os, 0) / 10000) - 100 }
-
-// CopyPaths is a generic implementation of [hst.Paths].
-func CopyPaths(os State, v *hst.Paths, userid int) {
-	if tempDir, err := container.NewAbs(os.TempDir()); err != nil {
-		log.Fatalf("invalid TMPDIR: %v", err)
-	} else {
-		v.TempDir = tempDir
-	}
-
-	v.SharePath = v.TempDir.Append("hakurei." + strconv.Itoa(userid))
-	hlog.Verbosef("process share directory at %q", v.SharePath)
-
-	r, _ := os.LookupEnv(xdgRuntimeDir)
-	if a, err := container.NewAbs(r); err != nil {
-		// fall back to path in share since hakurei has no hard XDG dependency
-		v.RunDirPath = v.SharePath.Append("run")
-		v.RuntimePath = v.RunDirPath.Append("compat")
-	} else {
-		v.RuntimePath = a
-		v.RunDirPath = v.RuntimePath.Append("hakurei")
-	}
-	hlog.Verbosef("runtime directory at %q", v.RunDirPath)
-}
diff --git a/internal/sys/std.go b/internal/sys/std.go
deleted file mode 100644
index 11334c7..0000000
--- a/internal/sys/std.go
+++ /dev/null
@@ -1,44 +0,0 @@
-package sys
-
-import (
-	"io/fs"
-	"os"
-	"os/exec"
-	"os/user"
-	"path/filepath"
-	"sync"
-
-	"hakurei.app/container"
-	"hakurei.app/hst"
-	"hakurei.app/internal"
-	"hakurei.app/internal/hlog"
-)
-
-// Std implements System using the standard library.
-type Std struct {
-	paths     hst.Paths
-	pathsOnce sync.Once
-	Hsu
-}
-
-func (s *Std) Getuid() int                                  { return os.Getuid() }
-func (s *Std) Getgid() int                                  { return os.Getgid() }
-func (s *Std) LookupEnv(key string) (string, bool)          { return os.LookupEnv(key) }
-func (s *Std) TempDir() string                              { return os.TempDir() }
-func (s *Std) LookPath(file string) (string, error)         { return exec.LookPath(file) }
-func (s *Std) MustExecutable() string                       { return container.MustExecutable() }
-func (s *Std) LookupGroup(name string) (*user.Group, error) { return user.LookupGroup(name) }
-func (s *Std) ReadDir(name string) ([]os.DirEntry, error)   { return os.ReadDir(name) }
-func (s *Std) Stat(name string) (fs.FileInfo, error)        { return os.Stat(name) }
-func (s *Std) Open(name string) (fs.File, error)            { return os.Open(name) }
-func (s *Std) EvalSymlinks(path string) (string, error)     { return filepath.EvalSymlinks(path) }
-func (s *Std) Exit(code int)                                { internal.Exit(code) }
-func (s *Std) Println(v ...any)                             { hlog.Verbose(v...) }
-func (s *Std) Printf(format string, v ...any)               { hlog.Verbosef(format, v...) }
-
-const xdgRuntimeDir = "XDG_RUNTIME_DIR"
-
-func (s *Std) Paths() hst.Paths {
-	s.pathsOnce.Do(func() { CopyPaths(s, &s.paths, MustGetUserID(s)) })
-	return s.paths
-}
diff --git a/test/test.py b/test/test.py
index ae4dfda..a1e6b0f 100644
--- a/test/test.py
+++ b/test/test.py
@@ -100,7 +100,7 @@ print(machine.fail("sudo -u alice -i hsu"))
 # Verify hsu fault behaviour:
 if denyOutput != "hsu: uid 1001 is not in the hsurc file\n":
     raise Exception(f"unexpected deny output:\n{denyOutput}")
-if denyOutputVerbose != "hsu: uid 1001 is not in the hsurc file\nhakurei: *cannot obtain uid from setuid wrapper: current user is not in the hsurc file\n":
+if denyOutputVerbose != "hsu: uid 1001 is not in the hsurc file\nhakurei: *cannot retrieve user id from setuid wrapper: current user is not in the hsurc file\n":
     raise Exception(f"unexpected deny verbose output:\n{denyOutputVerbose}")
 
 # Verify timeout behaviour: