Domain Model

rim-domain owns the editor as a pure state machine.

Core Aggregate

The center of the domain is EditorState. It owns:

buffers and their text/history
tabs and windows
active tab and active window routing
cursor, selection, preferred column, and insert/visual state
window-local buffer views

Workbench state is deliberately excluded.

classDiagram
    class EditorState {
      +active_tab
      +mode
      +buffers
      +tabs
      +window_buffer_views
      +preferred_display_col
    }
    class BufferState {
      +path
      +text
      +clean_text
      +undo_stack
      +redo_stack
    }
    class TabState {
      +windows
      +active_window
      +buffer_order
    }
    class WindowState {
      +buffer_id
      +x
      +y
      +width
      +height
    }
    EditorState --> BufferState
    EditorState --> TabState
    TabState --> WindowState

What Belongs Here

cursor movement
visual selection math
text mutations
undo/redo state transitions
tab/window/buffer transitions that are editor-pure
session snapshot and restore rules

What Does Not Belong Here

command palette state
picker cache and loading state
notifications
status bar messaging
config parsing or reload behavior
filesystem watcher coordination

Invariants

Important domain invariants include:

the active tab must exist
the active window must exist inside the active tab
cursors and selections must be clamped to the active buffer text
session restore must reject incompatible snapshots instead of partially restoring invalid state

Persistence Compatibility

The domain owns snapshot shapes such as WorkspaceSessionSnapshot and persisted history structures. That keeps storage adapters from inventing their own editor model.

The storage format is still preserved for compatibility. The architecture change did not justify a persistence break.

Anti-Patterns

Passing Terminal or Renderer data into rim-domain
Returning display messages instead of typed editor outcomes
Storing config-derived registries in domain structs