app: remove split implementation

It is completely nonsensical and highly error-prone to have multiple implementations of this in the same build. This should be switched at compile time instead therefore the split packages are pointless.

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

internal/app/app.go

@@ -0,0 +1,61 @@
+// Package app defines the generic [App] interface.
+package app
+
+import (
+	"context"
+	"log"
+	"syscall"
+	"time"
+
+	"hakurei.app/hst"
+	"hakurei.app/internal/app/state"
+	"hakurei.app/internal/sys"
+)
+
+type App interface {
+	// ID returns a copy of [ID] held by App.
+	ID() state.ID
+
+	// Seal determines the outcome of config as a [SealedApp].
+	// The value of config might be overwritten and must not be used again.
+	Seal(config *hst.Config) (SealedApp, error)
+
+	String() string
+}
+
+type SealedApp interface {
+	// Run commits sealed system setup and starts the app process.
+	Run(rs *RunState) error
+}
+
+// RunState stores the outcome of a call to [SealedApp.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
+}
+
+// SetStart stores the current time in [RunState] once.
+func (rs *RunState) SetStart() {
+	if rs.Time != nil {
+		panic("attempted to store time twice")
+	}
+	now := time.Now().UTC()
+	rs.Time = &now
+}
+
+func MustNew(ctx context.Context, os sys.State) App {
+	a, err := New(ctx, os)
+	if err != nil {
+		log.Fatalf("cannot create app: %v", err)
+	}
+	return a
+}