fix: harden Pi lifecycle recovery

tools/thothctl/internal/pi/durable_unix.go

@@ -2,14 +2,34 @@
 
 package pi
 
-import "os"
+import (
+	"errors"
+	"os"
+	"path/filepath"
+)
 
 // durableReplace acknowledges both the data file and its directory entry. A successful return
 // is the strongest atomic replacement guarantee supported by Unix filesystems.
 func durableReplace(temporary, target, directory string) error {
-	if err := os.Rename(temporary, target); err != nil { return err }
+	if err := os.Rename(temporary, target); err != nil {
+		return err
+	}
 	dir, err := os.Open(directory)
-	if err != nil { return err }
+	if err != nil {
+		return err
+	}
+	defer dir.Close()
+	return dir.Sync()
+}
+
+func durableRemove(path string) error {
+	if err := os.Remove(path); err != nil && !errors.Is(err, os.ErrNotExist) {
+		return err
+	}
+	dir, err := os.Open(filepath.Dir(path))
+	if err != nil {
+		return err
+	}
 	defer dir.Close()
 	return dir.Sync()
 }