When coding in not too wide buffer flycheck errors tally that should be visible in line-mode gets truncated. How do I guarantee that flycheck mode tally comes first in the order of major/minor modes in line-mode?
The minor modes are displayed in the order of minor-mode-alist. By default this simply reflects the load order (hence the kind-of-workaround you noted, but noting that the workaround would fail once additional minor modes were loaded).
Manipulating the list after libraries are loaded lets you maintain a desired display order on an ongoing basis.
(defun my-promote-flycheck (&optional _file)
"Give `flycheck-mode' priority position in `minor-mode-alist'.
Called via `after-load-functions', as well as `after-init-hook'."
(unless (eq (caar minor-mode-alist) 'flycheck-mode)
(let ((found (assq 'flycheck-mode minor-mode-alist)))
(when found
(assq-delete-all 'flycheck-mode minor-mode-alist)
(push found minor-mode-alist)))))
(add-hook 'after-load-functions 'my-promote-flycheck)
(add-hook 'after-init-hook 'my-promote-flycheck)