ensure file moves do not occur across filesystems

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

store.go

@@ -152,6 +152,7 @@ func (s *Store) AddTool(toolName string, resolvedVersion, pathOutsideRoot string
 	// move the file into the store at root/basename
 	targetName := toolName
 	targetPath := filepath.Join(s.root, toolName)
+
 	if err := os.Rename(pathOutsideRoot, targetPath); err != nil {
 		return err
 	}

tool/install.go

@@ -28,7 +28,12 @@ func Install(tool binny.Tool, intent binny.VersionIntent, store *binny.Store, ve
 		}
 	}()
 
-	tmpdir, err := os.MkdirTemp("", fmt.Sprintf("binny-install-%s-", tool.Name()))
+	// note: we choose a staging directory that is within the store to ensure the final move is atomic
+	// and not across filesystems (which would not succeed). We do this instead of a copy in case one of the binaries
+	// being managed is in use, in which case a copy would fail with "text file busy" error, whereas a move would
+	// allow for the in-use binary to continue to be used (since an unlink is performed on the path to the binary
+	// or the path to the parent of the binary).
+	tmpdir, err := os.MkdirTemp(store.Root(), fmt.Sprintf("binny-install-%s-", tool.Name()))
 	if err != nil {
 		return fmt.Errorf("failed to create temp directory: %w", err)
 	}