Provides color-safe ANSI rendering functions (visible_len, truncate_visible, wrap_plain, progress_bar, rnu_gutter) and a signal-safe raw mode guard that restores cooked tty on SIGTSTP and re-enters raw on resume. All functions are self-contained with no external dependencies, making them reusable in any terminal application.

Translates Vim-style key notation (e.g., '<Esc>', '<C-x>') into raw byte sequences. Used by the grader and remap folding logic. Pure function, no internal imports, easily extractable for any project needing to parse or generate Vim key sequences.

Implements atomic JSON writes using a temporary file and os.replace, ensuring data integrity against partial writes. Provides load/save for skills and progress. The _atomic_write helper is a reusable pattern for safe file persistence in any Python application.

Contains the remap_blocks_skill function that checks if a user-defined key remap shadows a taught key in both key_commands and actual solutions. Also implements the Leitner box spaced repetition logic with ease multipliers and softened demotion. The collision detection pattern is reusable for any configurable keybinding system.