Undo/Redo

User expects Ctrl+Z to reverse the last action. Implementation:

Command pattern:

• Each edit is a command with do() and undo().
• Stack of commands; pop to undo.

Undo stack:

Redo: separate stack. Cleared on new edit.

Grouping:

• Single Ctrl+Z should undo a "logical" action.
• Typing a word: each letter shouldn't undo individually.
• Group consecutive insertions within timeout (e.g., 1 second).
• Or: explicit boundaries (Enter, paste, etc.).

Persistent undo (rope-based):

• Tree of versions; each edit creates a new node.
• Undo = move pointer to parent.
• Redo = move to child.
• Branching: undo + edit creates a new branch.
• Like Git for editor state.

Vim's undo tree is famous: g- and g+ navigate it.

Memory:

• Per-edit memory cost.
• Big paste = big undo entry.
• Truncate after some max history depth or memory limit.