- Removed the built-in `background` (`bg`) slash command and its `handleBackgroundCommand` path from the interactive flow.
- Deleted background event subscription and shutdown handling by removing `handleBackgroundEvent` from the event, input, and interactive controllers.
- Simplified `InteractiveModeContext` by dropping background-only fields and helpers such as `isBackgrounded`, background UI context creation, and background event callbacks.
- Dropped `summarizeShakeRegions`, the shake-summary prompt, and related types.
- Removed `shake-summary` compaction strategy and `providers.shakeSummaryModel` setting.
- Migrated existing `shake-summary` configs to plain `shake` on load.
- Simplified `/shake` to `elide` and `images` modes only.