system updater: complete overhaul

Move system update flow to GO, with a CLI (convenient AIO tool) and
server integration. All lifecycle, scheduling, execution occurs on
backend side.

Run some backends via pkexec, some via terminal like paru/yay.

Incorporate flatpak as an option to update.

Add terminal override setting in GUI, in addition to $TERMINAL env
variable.

fixes #2307
fixes #822
fixes #1102
fixes #1812
fixes #1087
fixes #1743

core/internal/server/sysupdate/backend_rpmostree.go

@@ -0,0 +1,125 @@
+package sysupdate
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"os/exec"
+)
+
+const ostreeExitUpdateAvailable = 77
+
+func init() {
+	RegisterSystemBackend(func() Backend { return &rpmOstreeBackend{} })
+}
+
+type rpmOstreeBackend struct{}
+
+func (rpmOstreeBackend) ID() string           { return "rpm-ostree" }
+func (rpmOstreeBackend) DisplayName() string  { return "rpm-ostree" }
+func (rpmOstreeBackend) Repo() RepoKind       { return RepoOSTree }
+func (rpmOstreeBackend) NeedsAuth() bool      { return true }
+func (rpmOstreeBackend) RunsInTerminal() bool { return false }
+
+func (b rpmOstreeBackend) IsAvailable(ctx context.Context) bool {
+	if !commandExists("rpm-ostree") {
+		return false
+	}
+	return ostreeBooted(ctx)
+}
+
+type ostreeStatus struct {
+	Deployments  []ostreeDeployment `json:"deployments"`
+	CachedUpdate *ostreeCached      `json:"cached-update"`
+}
+
+type ostreeDeployment struct {
+	Origin    string `json:"origin"`
+	Version   string `json:"version"`
+	Timestamp int64  `json:"timestamp"`
+	Booted    bool   `json:"booted"`
+}
+
+type ostreeCached struct {
+	Origin    string `json:"origin"`
+	Version   string `json:"version"`
+	Timestamp int64  `json:"timestamp"`
+	Checksum  string `json:"checksum"`
+}
+
+func ostreeBooted(ctx context.Context) bool {
+	cmd := exec.CommandContext(ctx, "rpm-ostree", "status", "--json")
+	out, err := cmd.Output()
+	if err != nil {
+		return false
+	}
+	var s ostreeStatus
+	if err := json.Unmarshal(out, &s); err != nil {
+		return false
+	}
+	return len(s.Deployments) > 0
+}
+
+func (rpmOstreeBackend) CheckUpdates(ctx context.Context) ([]Package, error) {
+	cmd := exec.CommandContext(ctx, "rpm-ostree", "upgrade", "--check")
+	if err := cmd.Run(); err != nil {
+		exitErr, ok := errors.AsType[*exec.ExitError](err)
+		if !ok || exitErr.ExitCode() != ostreeExitUpdateAvailable {
+			return nil, err
+		}
+	}
+
+	statusOut, err := exec.CommandContext(ctx, "rpm-ostree", "status", "--json").Output()
+	if err != nil {
+		return nil, err
+	}
+	return parseRpmOstreeStatus(statusOut)
+}
+
+func parseRpmOstreeStatus(statusOut []byte) ([]Package, error) {
+	var s ostreeStatus
+	if err := json.Unmarshal(statusOut, &s); err != nil {
+		return nil, err
+	}
+	if s.CachedUpdate == nil {
+		return nil, nil
+	}
+
+	booted := bootedDeployment(s.Deployments)
+	from := ""
+	if booted != nil {
+		from = booted.Version
+	}
+	if from == s.CachedUpdate.Version {
+		return nil, nil
+	}
+
+	name := s.CachedUpdate.Origin
+	if name == "" {
+		name = "system"
+	}
+	return []Package{{
+		Name:        name,
+		Repo:        RepoOSTree,
+		Backend:     "rpm-ostree",
+		FromVersion: from,
+		ToVersion:   s.CachedUpdate.Version,
+	}}, nil
+}
+
+func bootedDeployment(deps []ostreeDeployment) *ostreeDeployment {
+	for i := range deps {
+		if deps[i].Booted {
+			return &deps[i]
+		}
+	}
+	return nil
+}
+
+func (rpmOstreeBackend) Upgrade(ctx context.Context, opts UpgradeOptions, onLine func(string)) error {
+	argv := []string{"rpm-ostree", "upgrade"}
+	if opts.DryRun {
+		argv = append(argv, "--check")
+	}
+	return Run(ctx, argv, RunOptions{OnLine: onLine})
+}