Cherry-pick #25423 to 7.13: Do not use unversioned home with watcher binary path

x-pack/elastic-agent/CHANGELOG.next.asciidoc

@@ -61,6 +61,7 @@
 - Reduce log level for listener cleanup to debug {pull}25274[25274]
 - Delay the restart of application when a status report of failure is given {pull}25339[25339]
 - Don't log when upgrade capability doesn't apply {pull}25386[25386]
+- Fixed issue when unversioned home is set and invoked watcher failing with ENOENT {issue}25371[25371]
 
 ==== New features
 

x-pack/elastic-agent/pkg/agent/application/paths/common.go

@@ -75,7 +75,7 @@ func Home() string {
 	if unversionedHome {
 		return topPath
 	}
-	return versionedHome(topPath)
+	return VersionedHome(topPath)
 }
 
 // IsVersionHome returns true if the Home path is versioned based on build.
@@ -134,6 +134,11 @@ func SetLogs(path string) {
 	logsPath = path
 }
 
+// VersionedHome returns a versioned path based on a TopPath and used commit.
+func VersionedHome(base string) string {
+	return filepath.Join(base, "data", fmt.Sprintf("elastic-agent-%s", release.ShortCommit()))
+}
+
 // initialTop returns the initial top-level path for the binary
 //
 // When nested in top-level/data/elastic-agent-${hash}/ the result is top-level/.
@@ -163,7 +168,3 @@ func insideData(exePath string) bool {
 	expectedPath := filepath.Join("data", fmt.Sprintf("elastic-agent-%s", release.ShortCommit()))
 	return strings.HasSuffix(exePath, expectedPath)
 }
-
-func versionedHome(base string) string {
-	return filepath.Join(base, "data", fmt.Sprintf("elastic-agent-%s", release.ShortCommit()))
-}

x-pack/elastic-agent/pkg/agent/application/upgrade/rollback.go

@@ -101,7 +101,8 @@ func InvokeWatcher(log *logger.Logger) error {
 		return nil
 	}
 
-	cmd := invokeCmd()
+	versionedHome := paths.VersionedHome(paths.Top())
+	cmd := invokeCmd(versionedHome)
 	defer func() {
 		if cmd.Process != nil {
 			log.Debugf("releasing watcher %v", cmd.Process.Pid)

x-pack/elastic-agent/pkg/agent/application/upgrade/service.go

@@ -200,8 +200,8 @@ func (p *noopPidProvider) Name() string { return "noop" }
 
 func (p *noopPidProvider) PID(ctx context.Context) (int, error) { return 0, nil }
 
-func invokeCmd() *exec.Cmd {
-	homeExePath := filepath.Join(paths.Home(), agentName)
+func invokeCmd(topPath string) *exec.Cmd {
+	homeExePath := filepath.Join(topPath, agentName)
 
 	cmd := exec.Command(homeExePath, watcherSubcommand,
 		"--path.config", paths.Config(),

x-pack/elastic-agent/pkg/agent/application/upgrade/service_darwin.go

@@ -113,8 +113,8 @@ func (p *darwinPidProvider) piderFromCmd(ctx context.Context, name string, args
 	}
 }
 
-func invokeCmd() *exec.Cmd {
-	homeExePath := filepath.Join(paths.Home(), agentName)
+func invokeCmd(topPath string) *exec.Cmd {
+	homeExePath := filepath.Join(topPath, agentName)
 
 	cmd := exec.Command(homeExePath, watcherSubcommand,
 		"--path.config", paths.Config(),

x-pack/elastic-agent/pkg/agent/application/upgrade/service_windows.go

@@ -61,8 +61,8 @@ func (p *pidProvider) PID(ctx context.Context) (int, error) {
 	return int(status.ProcessId), nil
 }
 
-func invokeCmd() *exec.Cmd {
-	homeExePath := filepath.Join(paths.Home(), agentName)
+func invokeCmd(topPath string) *exec.Cmd {
+	homeExePath := filepath.Join(topPath, agentName)
 
 	cmd := exec.Command(homeExePath, watcherSubcommand,
 		"--path.config", paths.Config(),