Module command_line_expand_mode 

MB.2 (rich minibuffer, tier 2): command-line-expand-mode.

When the user presses <C-x><C-e> in the : line, the one-row *command-line* buffer grows into a full-modal mini-buffer band. This mode replaces command-line-mode as the buffer’s major for the duration of the expand, giving the expanded band its own isolated option stack (Number = false, SignColumn = No, etc.) and keymap surface.

Collapsing (<C-x><C-e> again) reactivates command-line-mode.

The mode is intentionally a separate ModeId so that:

• option overrides (gutter, line numbers, wrap) are scoped to the expanded band and never leak to the document pane;
• future expand-specific features (full-text syntax highlighting, per-line decorations, band-shaped render path) have a dedicated mode to attach to.

Structs

CommandLineExpandMode

command-line-expand-mode: the major mode of the *command-line* buffer while expanded into the full-modal band.