Keep recovery handoffs available after publication cancellation

internal/gotool/recovery.go

@@ -8,6 +8,8 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"strconv"
+	"strings"
 
 	"golang.org/x/mod/modfile"
 
@@ -17,6 +19,30 @@ import (
 const releaseKitModule = "go.maximumdirect.net/releasekit"
 const releaseKitCommand = releaseKitModule + "/cmd/releasekit"
 
+// TemporaryExecutable recognizes executables in Go's temporary build layout,
+// <work parent>/go-build<nonce>/b<action>/exe/<name>. Those paths disappear when
+// the Go driver finishes and cannot provide a later native-command fallback.
+func TemporaryExecutable(path string) bool {
+	exeDir := filepath.Dir(path)
+	if filepath.Base(exeDir) != "exe" {
+		return false
+	}
+	actionDir := filepath.Dir(exeDir)
+	action, ok := strings.CutPrefix(filepath.Base(actionDir), "b")
+	if !ok || action == "" {
+		return false
+	}
+	if _, err := strconv.ParseUint(action, 10, 64); err != nil {
+		return false
+	}
+	nonce, ok := strings.CutPrefix(filepath.Base(filepath.Dir(actionDir)), "go-build")
+	if !ok || nonce == "" {
+		return false
+	}
+	_, err := strconv.ParseUint(nonce, 10, 64)
+	return err == nil
+}
+
 // RecoveryTool returns module-selected Go arguments for a later invocation.
 // An empty result means this module does not select ReleaseKit. API-only modules
 // receive a private module root that outlives launcher-owned bootstraps.