internal/app: do not return from shim start

The whole RunState ugliness and the other horrendous error handling conditions for internal/app come from an old design proposal for maintaining all app containers under the same daemon process for a user. The proposal was ultimately rejected but the implementation remained. It is removed here to alleviate internal/app from much of its ugliness and unreadability.

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

8 files changed, 297 insertions, 393 deletions

diff --git a/internal/app/errors.go b/internal/app/errors.go
deleted file mode 100644
index f7fa2b1c..00000000
--- a/internal/app/errors.go
+++ /dev/null
@@ -1,184 +0,0 @@
-package app
-
-import (
-	"errors"
-	"log"
-
-	"hakurei.app/container"
-	"hakurei.app/hst"
-	"hakurei.app/internal/hlog"
-	"hakurei.app/internal/sys"
-)
-
-// PrintRunStateErr prints an error message via [log] if runErr is not nil, and returns an appropriate exit code.
-//
-// TODO(ophestra): remove this function once RunState has been replaced
-func PrintRunStateErr(rs *RunState, runErr error) (code int) {
-	code = rs.ExitStatus()
-
-	if runErr != nil {
-		if rs.Time == nil {
-			// no process has been created
-			printMessageError("cannot start app:", runErr)
-		} else {
-			if m, ok := container.GetErrorMessage(runErr); !ok {
-				// catch-all for unexpected errors
-				log.Println("run returned error:", runErr)
-			} else {
-				var se *StateStoreError
-				if !errors.As(runErr, &se) {
-					// this could only be returned from a shim setup failure path
-					log.Print(m)
-				} else {
-					// InnerErr is returned by c.Save(&sd, seal.ct), and are always unwrapped
-					printMessageError("error returned during revert:",
-						&hst.AppError{Step: "save process state", Err: se.InnerErr})
-				}
-			}
-		}
-
-		if code == 0 {
-			code = 126
-		}
-	}
-
-	if rs.RevertErr != nil {
-		var stateStoreError *StateStoreError
-		if !errors.As(rs.RevertErr, &stateStoreError) || stateStoreError == nil {
-			printMessageError("cannot clean up:", rs.RevertErr)
-			goto out
-		}
-
-		if stateStoreError.Errs != nil {
-			if len(stateStoreError.Errs) == 2 { // storeErr.save(revertErr, store.Close())
-				if stateStoreError.Errs[0] != nil { // revertErr is MessageError joined by errors.Join
-					var joinedErrors interface {
-						Unwrap() []error
-						error
-					}
-					if !errors.As(stateStoreError.Errs[0], &joinedErrors) {
-						printMessageError("cannot revert:", stateStoreError.Errs[0])
-					} else {
-						for _, err := range joinedErrors.Unwrap() {
-							if err != nil {
-								printMessageError("cannot revert:", err)
-							}
-						}
-					}
-				}
-				if stateStoreError.Errs[1] != nil { // store.Close() is joined by errors.Join
-					log.Printf("cannot close store: %v", stateStoreError.Errs[1])
-				}
-			} else {
-				log.Printf("fault during cleanup: %v", errors.Join(stateStoreError.Errs...))
-			}
-		}
-
-		if stateStoreError.OpErr != nil {
-			log.Printf("blind revert due to store fault: %v", stateStoreError.OpErr)
-		}
-
-		if stateStoreError.DoErr != nil {
-			printMessageError("state store operation unsuccessful:", stateStoreError.DoErr)
-		}
-
-		if stateStoreError.Inner && stateStoreError.InnerErr != nil {
-			printMessageError("cannot destroy state entry:", stateStoreError.InnerErr)
-		}
-
-	out:
-		if code == 0 {
-			code = 128
-		}
-	}
-	if rs.WaitErr != nil {
-		hlog.Verbosef("wait: %v", rs.WaitErr)
-	}
-	return
-}
-
-// TODO(ophestra): this duplicates code in cmd/hakurei/command.go, keep this up to date until removal
-func printMessageError(fallback string, err error) {
-	// this indicates the error message has already reached stderr, outside the current process's control;
-	// this is only reached when hsu fails for any reason, as a second error message following hsu is confusing
-	if errors.Is(err, sys.ErrHsuAccess) {
-		hlog.Verbose("*"+fallback, err)
-		return
-	}
-
-	m, ok := container.GetErrorMessage(err)
-	if !ok {
-		log.Println(fallback, err)
-		return
-	}
-
-	log.Print(m)
-}
-
-// StateStoreError is returned for a failed state save.
-type StateStoreError struct {
-	// whether inner function was called
-	Inner bool
-	// returned by the Save/Destroy method of [state.Cursor]
-	InnerErr error
-	// returned by the Do method of [state.Store]
-	DoErr error
-	// stores an arbitrary store operation error
-	OpErr error
-	// stores arbitrary errors
-	Errs []error
-}
-
-// save saves arbitrary errors in [StateStoreError.Errs] once.
-func (e *StateStoreError) save(errs ...error) {
-	if len(errs) == 0 || e.Errs != nil {
-		panic("invalid call to save")
-	}
-	e.Errs = errs
-}
-
-// equiv returns an error that [StateStoreError] is equivalent to, including nil.
-func (e *StateStoreError) equiv(step string) error {
-	if e.Inner && e.InnerErr == nil && e.DoErr == nil && e.OpErr == nil && errors.Join(e.Errs...) == nil {
-		return nil
-	} else {
-		return &hst.AppError{Step: step, Err: e}
-	}
-}
-
-func (e *StateStoreError) Error() string {
-	if e.Inner && e.InnerErr != nil {
-		return e.InnerErr.Error()
-	}
-	if e.DoErr != nil {
-		return e.DoErr.Error()
-	}
-	if e.OpErr != nil {
-		return e.OpErr.Error()
-	}
-	if err := errors.Join(e.Errs...); err != nil {
-		return err.Error()
-	}
-
-	// equiv nullifies e for values where this is reached
-	panic("unreachable")
-}
-
-func (e *StateStoreError) Unwrap() (errs []error) {
-	errs = make([]error, 0, 3+len(e.Errs))
-	if e.InnerErr != nil {
-		errs = append(errs, e.InnerErr)
-	}
-	if e.DoErr != nil {
-		errs = append(errs, e.DoErr)
-	}
-	if e.OpErr != nil {
-		errs = append(errs, e.OpErr)
-	}
-	for _, err := range e.Errs {
-		if err != nil {
-			errs = append(errs, err)
-		}
-	}
-	return
-}
diff --git a/internal/app/process.go b/internal/app/process.go
index daa7832a..0ee123a1 100644
--- a/internal/app/process.go
+++ b/internal/app/process.go
@@ -13,7 +13,6 @@ import (
 	"time"
 
 	"hakurei.app/container"
-	"hakurei.app/hst"
 	"hakurei.app/internal"
 	"hakurei.app/internal/app/state"
 	"hakurei.app/internal/hlog"
@@ -23,85 +22,166 @@ import (
 // duration to wait for shim to exit, after container WaitDelay has elapsed.
 const shimWaitTimeout = 5 * time.Second
 
-// ErrShimTimeout is returned when shim did not exit within shimWaitTimeout, after its WaitDelay has elapsed.
-// This is different from the container failing to terminate within its timeout period, as that is enforced
-// by the shim. This error is instead returned when there is a lockup in shim preventing it from completing.
-var ErrShimTimeout = errors.New("shim did not exit")
+// mainState holds persistent state bound to [Outcome.Main].
+type mainState struct {
+	// done is whether beforeExit has been called already.
+	done bool
 
-// RunState stores the outcome of a call to [Outcome.Run].
-type RunState struct {
 	// Time is the exact point in time where the process was created.
 	// Location must be set to UTC.
 	//
 	// Time is nil if no process was ever created.
 	Time *time.Time
-	// RevertErr is stored by the deferred revert call.
-	RevertErr error
-	// WaitErr is the generic error value created by the standard library.
-	WaitErr error
 
-	syscall.WaitStatus
+	seal    *Outcome
+	store   state.Store
+	cancel  context.CancelFunc
+	cmd     *exec.Cmd
+	cmdWait chan error
+
+	uintptr
 }
 
-// setStart stores the current time in [RunState] once.
-func (rs *RunState) setStart() {
-	if rs.Time != nil {
-		panic("attempted to store time twice")
+const (
+	// mainNeedsRevert indicates the call to Commit has succeeded.
+	mainNeedsRevert uintptr = 1 << iota
+	// mainNeedsDestroy indicates the instance state entry is present in the store.
+	mainNeedsDestroy
+)
+
+// beforeExit must be called immediately before a call to [os.Exit].
+func (ms mainState) beforeExit(isFault bool) {
+	if ms.done {
+		panic("attempting to call beforeExit twice")
 	}
-	now := time.Now().UTC()
-	rs.Time = &now
-}
+	ms.done = true
+	defer hlog.BeforeExit()
 
-// Run commits deferred system setup and starts the container.
-func (seal *Outcome) Run(rs *RunState) error {
-	if !seal.f.CompareAndSwap(false, true) {
-		// Run does much more than just starting a process; calling it twice, even if the first call fails, will result
-		// in inconsistent state that is impossible to clean up; return here to limit damage and hopefully give the
-		// other Run a chance to return
-		return errors.New("outcome: attempted to run twice")
+	if isFault && ms.cancel != nil {
+		ms.cancel()
 	}
 
-	if rs == nil {
-		panic("invalid state")
+	var hasErr bool
+	// updates hasErr but does not terminate
+	perror := func(err error, message string) {
+		hasErr = true
+		printMessageError("cannot "+message+":", err)
 	}
+	exitCode := 1
+	defer func() {
+		if hasErr {
+			os.Exit(exitCode)
+		}
+	}()
 
-	// read comp value early to allow for early failure
-	hsuPath := internal.MustHsuPath()
+	// this also handles wait for a non-fault termination
+	if ms.cmd != nil && ms.cmdWait != nil {
+		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 {
+			shimTimeoutCompensated += MaxShimWaitDelay
+		} else {
+			shimTimeoutCompensated += ms.seal.waitDelay
+		}
+		// this ties waitDone to ctx with the additional compensated timeout duration
+		go func() { <-ms.seal.ctx.Done(); time.Sleep(shimTimeoutCompensated); close(waitDone) }()
 
-	if err := seal.sys.Commit(); err != nil {
-		return err
+		select {
+		case err := <-ms.cmdWait:
+			wstatus, ok := ms.cmd.ProcessState.Sys().(syscall.WaitStatus)
+			if ok {
+				if v := wstatus.ExitStatus(); v != 0 {
+					hasErr = true
+					exitCode = v
+				}
+			}
+
+			if hlog.Load() {
+				if !ok {
+					if err != nil {
+						hlog.Verbosef("wait: %v", err)
+					}
+				} else {
+					switch {
+					case wstatus.Exited():
+						hlog.Verbosef("process %d exited with code %d", ms.cmd.Process.Pid, wstatus.ExitStatus())
+
+					case wstatus.CoreDump():
+						hlog.Verbosef("process %d dumped core", ms.cmd.Process.Pid)
+
+					case wstatus.Signaled():
+						hlog.Verbosef("process %d got %s", ms.cmd.Process.Pid, wstatus.Signal())
+
+					default:
+						hlog.Verbosef("process %d exited with status %#x", ms.cmd.Process.Pid, wstatus)
+					}
+				}
+			}
+
+		case <-waitDone:
+			hlog.Resume()
+			// this is only reachable when shim did not exit within shimWaitTimeout, after its WaitDelay has elapsed.
+			// This is different from the container failing to terminate within its timeout period, as that is enforced
+			// by the shim. This path is instead reached when there is a lockup in shim preventing it from completing.
+			log.Printf("process %d did not terminate", ms.cmd.Process.Pid)
+		}
+
+		hlog.Resume()
+		if ms.seal.sync != nil {
+			if err := ms.seal.sync.Close(); err != nil {
+				perror(err, "close wayland security context")
+			}
+		}
+		if ms.seal.dbusMsg != nil {
+			ms.seal.dbusMsg()
+		}
 	}
-	store := state.NewMulti(seal.runDirPath.String())
-	deferredStoreFunc := func(c state.Cursor) error { return nil } // noop until state in store
-	defer func() {
-		var revertErr error
-		storeErr := new(StateStoreError)
-		storeErr.Inner, storeErr.DoErr = store.Do(seal.user.identity.unwrap(), func(c state.Cursor) {
-			revertErr = func() error {
-				storeErr.InnerErr = deferredStoreFunc(c)
 
-				var rt system.Enablement
+	if ms.uintptr&mainNeedsRevert != 0 {
+		if ok, err := ms.store.Do(ms.seal.user.identity.unwrap(), func(c state.Cursor) {
+			if ms.uintptr&mainNeedsDestroy != 0 {
+				if err := c.Destroy(ms.seal.id.unwrap()); err != nil {
+					perror(err, "destroy state entry")
+				}
+			}
+
+			var rt system.Enablement
+			if states, err := c.Load(); err != nil {
+				// it is impossible to continue from this point;
+				// revert per-process state here to limit damage
 				ec := system.Process
-				if states, err := c.Load(); err != nil {
-					// revert per-process state here to limit damage
-					storeErr.OpErr = err
-					return seal.sys.Revert((*system.Criteria)(&ec))
-				} else {
-					if l := len(states); l == 0 {
-						ec |= system.User
+				if revertErr := ms.seal.sys.Revert((*system.Criteria)(&ec)); revertErr != nil {
+					var joinError interface {
+						Unwrap() []error
+						error
+					}
+					if !errors.As(revertErr, &joinError) || joinError == nil {
+						perror(revertErr, "revert system setup")
 					} else {
-						hlog.Verbosef("found %d instances, cleaning up without user-scoped operations", l)
+						for _, v := range joinError.Unwrap() {
+							perror(v, "revert system setup step")
+						}
 					}
+				}
+				perror(err, "load instance states")
+			} else {
+				ec := system.Process
+				if l := len(states); l == 0 {
+					ec |= system.User
+				} else {
+					hlog.Verbosef("found %d instances, cleaning up without user-scoped operations", l)
+				}
 
-					// accumulate enablements of remaining launchers
-					for i, s := range states {
-						if s.Config != nil {
-							rt |= s.Config.Enablements.Unwrap()
-						} else {
-							log.Printf("state entry %d does not contain config", i)
-						}
+				// accumulate enablements of remaining launchers
+				for i, s := range states {
+					if s.Config != nil {
+						rt |= s.Config.Enablements.Unwrap()
+					} else {
+						log.Printf("state entry %d does not contain config", i)
 					}
 				}
+
 				ec |= rt ^ (system.EWayland | system.EX11 | system.EDBus | system.EPulse)
 				if hlog.Load() {
 					if ec > 0 {
@@ -109,27 +189,70 @@ func (seal *Outcome) Run(rs *RunState) error {
 					}
 				}
 
-				return seal.sys.Revert((*system.Criteria)(&ec))
-			}()
-		})
-		storeErr.save(revertErr, store.Close())
-		rs.RevertErr = storeErr.equiv("clean up")
-	}()
+				if err = ms.seal.sys.Revert((*system.Criteria)(&ec)); err != nil {
+					perror(err, "revert system setup")
+				}
+			}
+		}); err != nil {
+			if ok {
+				perror(err, "unlock state store")
+			} else {
+				perror(err, "open state store")
+			}
+		}
+	} else if ms.uintptr&mainNeedsDestroy != 0 {
+		panic("unreachable")
+	}
+
+	if ms.store != nil {
+		if err := ms.store.Close(); err != nil {
+			perror(err, "close state store")
+		}
+	}
+}
+
+// fatal calls printMessageError, performs necessary cleanup, followed by a call to [os.Exit](1).
+func (ms mainState) fatal(fallback string, ferr error) {
+	printMessageError(fallback, ferr)
+	ms.beforeExit(true)
+	os.Exit(1)
+}
+
+// Main commits deferred system setup, runs the container, reverts changes to the system, and terminates the program.
+// Main does not return.
+func (seal *Outcome) Main() {
+	if !seal.f.CompareAndSwap(false, true) {
+		panic("outcome: attempted to run twice")
+	}
+
+	// read comp value early for early failure
+	hsuPath := internal.MustHsuPath()
+
+	// ms.beforeExit required beyond this point
+	ms := &mainState{seal: seal}
+
+	if err := seal.sys.Commit(); err != nil {
+		ms.fatal("cannot commit system setup:", err)
+	}
+	ms.uintptr |= mainNeedsRevert
+	ms.store = state.NewMulti(seal.runDirPath.String())
 
 	ctx, cancel := context.WithCancel(seal.ctx)
 	defer cancel()
-	cmd := exec.CommandContext(ctx, hsuPath)
-	cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
-	cmd.Dir = container.FHSRoot // container init enters final working directory
+	ms.cancel = cancel
+
+	ms.cmd = exec.CommandContext(ctx, hsuPath)
+	ms.cmd.Stdin, ms.cmd.Stdout, ms.cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
+	ms.cmd.Dir = container.FHSRoot // container init enters final working directory
 	// shim runs in the same session as monitor; see shim.go for behaviour
-	cmd.Cancel = func() error { return cmd.Process.Signal(syscall.SIGCONT) }
+	ms.cmd.Cancel = func() error { return ms.cmd.Process.Signal(syscall.SIGCONT) }
 
 	var e *gob.Encoder
-	if fd, encoder, err := container.Setup(&cmd.ExtraFiles); err != nil {
-		return &hst.AppError{Step: "create shim setup pipe", Err: err}
+	if fd, encoder, err := container.Setup(&ms.cmd.ExtraFiles); err != nil {
+		ms.fatal("cannot create shim setup pipe:", err)
 	} else {
 		e = encoder
-		cmd.Env = []string{
+		ms.cmd.Env = []string{
 			// passed through to shim by hsu
 			shimEnv + "=" + strconv.Itoa(fd),
 			// interpreted by hsu
@@ -140,102 +263,78 @@ func (seal *Outcome) Run(rs *RunState) error {
 	if len(seal.user.supp) > 0 {
 		hlog.Verbosef("attaching supplementary group ids %s", seal.user.supp)
 		// interpreted by hsu
-		cmd.Env = append(cmd.Env, "HAKUREI_GROUPS="+strings.Join(seal.user.supp, " "))
+		ms.cmd.Env = append(ms.cmd.Env, "HAKUREI_GROUPS="+strings.Join(seal.user.supp, " "))
 	}
 
 	hlog.Verbosef("setuid helper at %s", hsuPath)
 	hlog.Suspend()
-	if err := cmd.Start(); err != nil {
-		return &hst.AppError{Step: "start setuid wrapper", Err: err}
+	if err := ms.cmd.Start(); err != nil {
+		ms.fatal("cannot start setuid wrapper:", err)
 	}
-	rs.setStart()
-
-	// this prevents blocking forever on an early failure
-	waitErr, setupErr := make(chan error, 1), make(chan error, 1)
-	go func() { waitErr <- cmd.Wait(); cancel() }()
-	go func() {
-		setupErr <- e.Encode(&shimParams{
-			os.Getpid(),
-			seal.waitDelay,
-			seal.container,
-			hlog.Load(),
-		})
-	}()
+	startTime := time.Now().UTC()
+	ms.cmdWait = make(chan error, 1)
+	// this ties context back to the life of the process
+	go func() { ms.cmdWait <- ms.cmd.Wait(); cancel() }()
+	ms.Time = &startTime
 
+	// unfortunately the I/O here cannot be directly canceled;
+	// the cancellation path leads to fatal in this case so that is fine
 	select {
-	case err := <-setupErr:
+	case err := <-func() (setupErr chan error) {
+		setupErr = make(chan error, 1)
+		go func() {
+			setupErr <- e.Encode(&shimParams{
+				os.Getpid(),
+				seal.waitDelay,
+				seal.container,
+				hlog.Load(),
+			})
+		}()
+		return
+	}():
 		if err != nil {
 			hlog.Resume()
-			return &hst.AppError{Step: "transmit shim config", Err: err}
+			ms.fatal("cannot transmit shim config:", err)
 		}
 
 	case <-ctx.Done():
 		hlog.Resume()
-		return newWithMessageError("shim setup canceled", syscall.ECANCELED)
+		ms.fatal("shim context canceled:", newWithMessageError("shim setup canceled", ctx.Err()))
 	}
 
-	// returned after blocking on waitErr
-	var earlyStoreErr = new(StateStoreError)
-	{
-		// shim accepted setup payload, create process state
-		sd := state.State{
+	// shim accepted setup payload, create process state
+	if ok, err := ms.store.Do(seal.user.identity.unwrap(), func(c state.Cursor) {
+		if err := c.Save(&state.State{
 			ID:   seal.id.unwrap(),
-			PID:  cmd.Process.Pid,
-			Time: *rs.Time,
+			PID:  ms.cmd.Process.Pid,
+			Time: *ms.Time,
+		}, seal.ct); err != nil {
+			ms.fatal("cannot save state entry:", err)
 		}
-		earlyStoreErr.Inner, earlyStoreErr.DoErr = store.Do(seal.user.identity.unwrap(), func(c state.Cursor) {
-			earlyStoreErr.InnerErr = c.Save(&sd, seal.ct)
-		})
-	}
-
-	// state in store at this point, destroy defunct state entry on return
-	deferredStoreFunc = func(c state.Cursor) error { return c.Destroy(seal.id.unwrap()) }
-
-	waitTimeout := make(chan struct{})
-	// TODO(ophestra): enforce this limit early so it does not have to be done twice
-	shimTimeoutCompensated := shimWaitTimeout
-	if seal.waitDelay > MaxShimWaitDelay {
-		shimTimeoutCompensated += MaxShimWaitDelay
-	} else {
-		shimTimeoutCompensated += seal.waitDelay
-	}
-	go func() { <-seal.ctx.Done(); time.Sleep(shimTimeoutCompensated); close(waitTimeout) }()
-
-	select {
-	case rs.WaitErr = <-waitErr:
-		rs.WaitStatus = cmd.ProcessState.Sys().(syscall.WaitStatus)
-		if hlog.Load() {
-			switch {
-			case rs.Exited():
-				hlog.Verbosef("process %d exited with code %d", cmd.Process.Pid, rs.ExitStatus())
-
-			case rs.CoreDump():
-				hlog.Verbosef("process %d dumped core", cmd.Process.Pid)
-
-			case rs.Signaled():
-				hlog.Verbosef("process %d got %s", cmd.Process.Pid, rs.Signal())
-
-			default:
-				hlog.Verbosef("process %d exited with status %#x", cmd.Process.Pid, rs.WaitStatus)
-			}
+	}); err != nil {
+		if ok {
+			ms.uintptr |= mainNeedsDestroy
+			ms.fatal("cannot unlock state store:", err)
+		} else {
+			ms.fatal("cannot open state store:", err)
 		}
-
-	case <-waitTimeout:
-		rs.WaitErr = ErrShimTimeout
-		hlog.Resume()
-		// TODO(ophestra): verify this behaviour in vm tests
-		log.Printf("process %d did not terminate", cmd.Process.Pid)
 	}
+	// state in store at this point, destroy defunct state entry on termination
+	ms.uintptr |= mainNeedsDestroy
 
-	hlog.Resume()
-	if seal.sync != nil {
-		if err := seal.sync.Close(); err != nil {
-			log.Printf("cannot close wayland security context: %v", err)
-		}
-	}
-	if seal.dbusMsg != nil {
-		seal.dbusMsg()
+	// beforeExit ties shim process to context
+	ms.beforeExit(false)
+	os.Exit(0)
+}
+
+// printMessageError prints the error message according to [container.GetErrorMessage],
+// or fallback prepended to err if an error message is not available.
+func printMessageError(fallback string, err error) {
+	m, ok := container.GetErrorMessage(err)
+	if !ok {
+		log.Println(fallback, err)
+		return
 	}
 
-	return earlyStoreErr.equiv("save process state")
+	log.Print(m)
 }
diff --git a/internal/app/seal.go b/internal/app/seal.go
index e6cccecc..cafd6915 100644
--- a/internal/app/seal.go
+++ b/internal/app/seal.go
@@ -119,7 +119,7 @@ type hsuUser struct {
 	username string
 }
 
-func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Config) error {
+func (seal *Outcome) finalise(ctx context.Context, k sys.State, config *hst.Config) error {
 	const (
 		home  = "HOME"
 		shell = "SHELL"
@@ -176,19 +176,17 @@ func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 		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))
 	}
-	if u, err := sys.Uid(seal.user.identity.unwrap()); err != nil {
-		return err
-	} else {
-		seal.user.uid = newInt(u)
-	}
+	seal.user.uid = newInt(sys.MustUid(k, seal.user.identity.unwrap()))
+
 	seal.user.supp = make([]string, len(config.Groups))
 	for i, name := range config.Groups {
-		if g, err := sys.LookupGroup(name); err != nil {
+		if g, err := k.LookupGroup(name); err != nil {
 			return newWithMessageError(fmt.Sprintf("unknown group %q", name), err)
 		} else {
 			seal.user.supp[i] = g.Gid
@@ -201,7 +199,7 @@ func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 
 		if config.Shell == nil {
 			config.Shell = container.AbsFHSRoot.Append("bin", "sh")
-			s, _ := sys.LookupEnv(shell)
+			s, _ := k.LookupEnv(shell)
 			if a, err := container.NewAbs(s); err == nil {
 				config.Shell = a
 			}
@@ -210,7 +208,7 @@ func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 		// hsu clears the environment so resolve paths early
 		if config.Path == nil {
 			if len(config.Args) > 0 {
-				if p, err := sys.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)
@@ -246,7 +244,7 @@ func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 
 		// hide nscd from container if present
 		nscd := container.AbsFHSVar.Append("run/nscd")
-		if _, err := sys.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}})
 		}
 
@@ -274,7 +272,7 @@ func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 	{
 		var uid, gid int
 		var err error
-		seal.container, seal.env, err = newContainer(config.Container, sys, seal.id.String(), &uid, &gid)
+		seal.container, seal.env, err = newContainer(config.Container, k, seal.id.String(), &uid, &gid)
 		seal.waitDelay = config.Container.WaitDelay
 		if err != nil {
 			return &hst.AppError{Step: "initialise container configuration", Err: err}
@@ -298,7 +296,7 @@ func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 	seal.env[xdgSessionClass] = "user"
 	seal.env[xdgSessionType] = "tty"
 
-	share := &shareHost{seal: seal, sc: sys.Paths()}
+	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)
@@ -342,14 +340,14 @@ func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 	}
 
 	// pass TERM for proper terminal I/O in initial process
-	if t, ok := sys.LookupEnv(term); ok {
+	if t, ok := k.LookupEnv(term); ok {
 		seal.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 := sys.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 {
@@ -380,7 +378,7 @@ func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 	}
 
 	if config.Enablements.Unwrap()&system.EX11 != 0 {
-		if d, ok := sys.LookupEnv(display); !ok {
+		if d, ok := k.LookupEnv(display); !ok {
 			return newWithMessage("DISPLAY is not set")
 		} else {
 			socketDir := container.AbsFHSTmp.Append(".X11-unix")
@@ -398,7 +396,7 @@ func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 				}
 			}
 			if socketPath != nil {
-				if _, err := sys.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}
 					}
@@ -422,14 +420,14 @@ func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 		// PulseAudio socket (usually `/run/user/%d/pulse/native`)
 		pulseSocket := pulseRuntimeDir.Append("native")
 
-		if _, err := sys.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 := sys.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}
 			}
@@ -453,7 +451,7 @@ func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 			const paLocateStep = "locate PulseAudio cookie"
 
 			// from environment
-			if p, ok := sys.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 {
@@ -464,14 +462,14 @@ func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 			}
 
 			// $HOME/.pulse-cookie
-			if p, ok := sys.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 := sys.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}
@@ -485,13 +483,13 @@ func (seal *Outcome) finalise(ctx context.Context, sys sys.State, config *hst.Co
 			}
 
 			// $XDG_CONFIG_HOME/pulse/cookie
-			if p, ok := sys.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 := sys.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}
diff --git a/internal/app/state/multi.go b/internal/app/state/multi.go
index 80a3abff..9a400ac6 100644
--- a/internal/app/state/multi.go
+++ b/internal/app/state/multi.go
@@ -27,27 +27,27 @@ type multiStore struct {
 	lock sync.RWMutex
 }
 
-func (s *multiStore) Do(aid int, f func(c Cursor)) (bool, error) {
+func (s *multiStore) Do(identity int, f func(c Cursor)) (bool, error) {
 	s.lock.RLock()
 	defer s.lock.RUnlock()
 
 	// load or initialise new backend
 	b := new(multiBackend)
 	b.lock.Lock()
-	if v, ok := s.backends.LoadOrStore(aid, b); ok {
+	if v, ok := s.backends.LoadOrStore(identity, b); ok {
 		b = v.(*multiBackend)
 	} else {
-		b.path = path.Join(s.base, strconv.Itoa(aid))
+		b.path = path.Join(s.base, strconv.Itoa(identity))
 
 		// ensure directory
 		if err := os.MkdirAll(b.path, 0700); err != nil && !errors.Is(err, fs.ErrExist) {
-			s.backends.CompareAndDelete(aid, b)
+			s.backends.CompareAndDelete(identity, b)
 			return false, err
 		}
 
 		// open locker file
 		if l, err := os.OpenFile(b.path+".lock", os.O_RDWR|os.O_CREATE, 0600); err != nil {
-			s.backends.CompareAndDelete(aid, b)
+			s.backends.CompareAndDelete(identity, b)
 			return false, err
 		} else {
 			b.lockfile = l
diff --git a/internal/app/state/state.go b/internal/app/state/state.go
index 42750ec6..6a3a82db 100644
--- a/internal/app/state/state.go
+++ b/internal/app/state/state.go
@@ -17,7 +17,7 @@ type Store interface {
 	// Do calls f exactly once and ensures store exclusivity until f returns.
 	// Returns whether f is called and any errors during the locking process.
 	// Cursor provided to f becomes invalid as soon as f returns.
-	Do(aid int, f func(c Cursor)) (ok bool, err error)
+	Do(identity int, f func(c Cursor)) (ok bool, err error)
 
 	// List queries the store and returns a list of aids known to the store.
 	// Note that some or all returned aids might not have any active apps.
diff --git a/internal/sys/hsu.go b/internal/sys/hsu.go
index 84bb0731..2be12d1e 100644
--- a/internal/sys/hsu.go
+++ b/internal/sys/hsu.go
@@ -3,6 +3,7 @@ package sys
 import (
 	"errors"
 	"fmt"
+	"log"
 	"os"
 	"os/exec"
 	"strconv"
@@ -11,6 +12,7 @@ import (
 	"hakurei.app/container"
 	"hakurei.app/hst"
 	"hakurei.app/internal"
+	"hakurei.app/internal/hlog"
 )
 
 // Hsu caches responses from cmd/hsu.
@@ -79,3 +81,24 @@ func (h *Hsu) Uid(identity int) (int, error) {
 	}
 	return u.uid, u.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
+	}
+
+	const fallback = "cannot obtain uid from setuid wrapper:"
+	if errors.Is(err, ErrHsuAccess) {
+		hlog.Verbose("*"+fallback, err)
+		os.Exit(1)
+		return -0xdeadbeef
+	} else if m, ok := container.GetErrorMessage(err); ok {
+		log.Fatal(m)
+		return -0xdeadbeef
+	} else {
+		log.Fatalln(fallback, err)
+		return -0xdeadbeef
+	}
+}
diff --git a/internal/sys/interface.go b/internal/sys/interface.go
index ed765ece..f2465e62 100644
--- a/internal/sys/interface.go
+++ b/internal/sys/interface.go
@@ -49,14 +49,8 @@ type State interface {
 	Uid(identity int) (int, error)
 }
 
-// GetUserID obtains user id from hsu by querying uid of identity 0.
-func GetUserID(os State) (int, error) {
-	if uid, err := os.Uid(0); err != nil {
-		return -1, err
-	} else {
-		return (uid / 10000) - 100, nil
-	}
-}
+// 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) {
diff --git a/internal/sys/std.go b/internal/sys/std.go
index 24b36fa2..11334c72 100644
--- a/internal/sys/std.go
+++ b/internal/sys/std.go
@@ -1,9 +1,7 @@
 package sys
 
 import (
-	"errors"
 	"io/fs"
-	"log"
 	"os"
 	"os/exec"
 	"os/user"
@@ -41,30 +39,6 @@ func (s *Std) Printf(format string, v ...any)               { hlog.Verbosef(form
 const xdgRuntimeDir = "XDG_RUNTIME_DIR"
 
 func (s *Std) Paths() hst.Paths {
-	s.pathsOnce.Do(func() {
-		if userid, err := GetUserID(s); err != nil {
-			// TODO(ophestra): this duplicates code in cmd/hakurei/command.go, keep this up to date until removal
-			hlog.BeforeExit()
-			const fallback = "cannot obtain user id from hsu:"
-
-			// this indicates the error message has already reached stderr, outside the current process's control;
-			// this is only reached when hsu fails for any reason, as a second error message following hsu is confusing
-			if errors.Is(err, ErrHsuAccess) {
-				hlog.Verbose("*"+fallback, err)
-				os.Exit(1)
-				return
-			}
-
-			m, ok := container.GetErrorMessage(err)
-			if !ok {
-				log.Fatalln(fallback, err)
-				return
-			}
-
-			log.Fatal(m)
-		} else {
-			CopyPaths(s, &s.paths, userid)
-		}
-	})
+	s.pathsOnce.Do(func() { CopyPaths(s, &s.paths, MustGetUserID(s)) })
 	return s.paths
 }