Module command 

Undoable command infrastructure for the undo/redo system.

This module provides the UndoableCmd trait for reversible operations and common command implementations for text editing and UI interactions.

Design Principles

1. Explicit state: Commands capture all state needed for undo/redo
2. Memory-efficient: Commands report their size for budget management
3. Mergeable: Consecutive similar commands can merge (e.g., typing)
4. Traceable: Commands include metadata for debugging and UI display

Invariants

• execute() followed by undo() restores prior state exactly
• undo() followed by redo() restores the executed state exactly
• Commands with can_merge() == true MUST successfully merge
• size_bytes() MUST be accurate for memory budgeting

Failure Modes

• Stale reference: Command holds reference to deleted target
  • Mitigation: Validate target existence in execute/undo
• State drift: External changes invalidate undo data
  • Mitigation: Clear undo stack on external modifications
• Memory exhaustion: Unbounded history growth
  • Mitigation: History stack enforces size limits via size_bytes()

Structs

CommandBatch

A batch of commands that execute and undo together.

CommandMetadata

Metadata attached to every command for tracing and UI display.

MergeConfig

Configuration for command merging behavior.

TextDeleteCmd

Command to delete text at a position.

TextInsertCmd

Command to insert text at a position.

TextReplaceCmd

Command to replace text at a position.

WidgetId

Unique identifier for a widget that commands operate on.

Enums

CommandError

Errors that can occur during command execution.

CommandSource

Source of a command - who/what triggered it.

Traits

UndoableCmd

A reversible command that can be undone and redone.

Type Aliases

CommandResult

Result of command execution or undo.

TextApplyFn

Callback type for applying text operations.

TextRemoveFn

Callback type for removing text.

TextReplaceFn

Callback type for replacing text.