internal/app: modularise outcome finalise

This is the initial effort of splitting up host and container side of finalisation for params to shim. The new layout also enables much finer grained unit testing of each step, as well as partition access to per-app state for each step.

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

internal/app/app_stub_test.go

@@ -1,7 +1,9 @@
 package app
 
 import (
+	"bytes"
 	"fmt"
+	"io"
 	"io/fs"
 	"log"
 	"os/exec"
@@ -52,12 +54,21 @@ func (k *stubNixOS) stat(name string) (fs.FileInfo, error) {
 	case "/home/ophestra/.pulse-cookie":
 		return stubFileInfoIsDir(true), nil
 	case "/home/ophestra/xdg/config/pulse/cookie":
-		return stubFileInfoIsDir(false), nil
+		return stubFileInfoPulseCookie{false}, nil
 	default:
 		panic(fmt.Sprintf("attempted to stat unexpected path %q", name))
 	}
 }
 
+func (k *stubNixOS) open(name string) (osFile, error) {
+	switch name {
+	case "/home/ophestra/xdg/config/pulse/cookie":
+		return stubOsFileReadCloser{io.NopCloser(bytes.NewReader(bytes.Repeat([]byte{0}, pulseCookieSizeMax)))}, nil
+	default:
+		panic(fmt.Sprintf("attempted to open unexpected path %q", name))
+	}
+}
+
 func (k *stubNixOS) readdir(name string) ([]fs.DirEntry, error) {
 	switch name {
 	case "/":