Clear context is restored in Home Chat

What changed

Home Chat again supports starting a fresh model context inside the current conversation, from Cmd/Ctrl+K, the input QuickPanel, or an optional composer eraser button. The eraser is hidden by default and can be added through toolbar customization. The conversation keeps the visible history and shows a context-boundary divider, while later model requests exclude messages before the most recent boundary on the selected branch.

Why this matters to the user

Users can reset what the model sees without creating a new conversation. Future v1-to-v2 migrations also preserve existing clear-context boundaries and their message-tree relationships.

What the user should do

Use Cmd/Ctrl+K or choose Clear Context from the input QuickPanel. Add the eraser button from the composer toolbar customization menu if a persistent visible shortcut is preferred.

Notes for release manager

Databases already migrated by an earlier v2 pre-release cannot reconstruct boundaries that were previously discarded. Those installations begin persisting new boundaries after this change.