Emacs

unobin-ts-mode is the Tree-sitter major mode for .ub files. It also registers unobin lsp with Eglot when Eglot is loaded.

(use-package unobin-ts-mode
  :ensure t
  :mode ("\\.ub\\'" . unobin-ts-mode)
  :custom
  (unobin-treesit-auto-install 'ask))

To start Eglot automatically in Unobin buffers:

(use-package unobin-ts-mode
  :ensure t
  :mode ("\\.ub\\'" . unobin-ts-mode)
  :custom
  (unobin-eglot-auto-start t)
  (unobin-treesit-auto-install 'ask))

The first .ub buffer asks to install the Tree-sitter grammar by default. Run M-x unobin-install-treesit-grammar to install it explicitly.

Completions come from Eglot. Run M-x eglot in a .ub buffer, then use M-x completion-at-point or a CAPF frontend such as Corfu or Company.

Keep the unobin executable on PATH so Eglot can start unobin lsp.