TUI stops applying all events after a message is removed in a session it never loaded #52584

Description

An attached TUI can silently stop updating. Your prompts still send and the agent replies (both are saved server-side), but the transcript never shows them until you reopen the window.

Cause: every TUI client gets every session's events. The message.removed and message.part.removed handlers in packages/tui/src/context/sync.tsx index into store state without checking it exists. So a removal in a session this client never loaded throws: undefined is not an object (evaluating 'store.message[event.properties.sessionID].findIndex'). The throw escapes the SSE loop in context/sdk.tsx, whose .catch(() => {}) swallows it. The client stays connected but never applies another event.

Removals come from revert cleanup (the next prompt after /undo) and the delete message/part endpoints. So one /undo + resend in any session freezes every other open client that hadn't loaded that session.

Plugins

None needed to reproduce

OpenCode version

1.18.34, and current dev

Steps to reproduce

1. opencode serve, with sessions A and B that both already have messages
2. opencode attach <url> --session A
3. Delete a message in B that existed before step 2: DELETE /session/B/message/<id> (or /undo in B and send a new prompt)
4. Send anything in A. It's saved and answered, but the attached window never shows it

Operating System

macOS

Terminal

Hyper, tmux