Conversation branching or forking is supported

When a conversation takes a wrong turn twenty messages deep — a bad file upload, a misread instruction, a hallucination that the model now treats as ground truth — users need a way to rewind and try a different path without losing the useful context that came before. A strictly linear conversation forces "delete the last ten messages or start a new chat" as the only exits, both of which throw away work. Branching preserves that work.

Start with edit-and-regenerate as the minimum viable branch. When a user edits a prior message, truncate state to that point and call reload() to regenerate from the edited turn. Full tree branching requires a parent_message_id column on the messages table and a tree-rendering sidebar; ship the minimum first. Implement in src/components/chat/message-actions.tsx.

setMessages(messages.slice(0, editIndex).concat({ ...messages[editIndex], content: newContent }))
reload()