Mode change failure is not rolled back (UI shows new mode, agent still on old)

[aasis21]

Problem

sendMode optimistically sets timeline.mode then sends. If the send fails, there's no rollback or error — the composer pill shows the new mode while the agent is still in the old one, silently diverging.

Suggested fix

Confirm the mode change from the extension (ack) before committing the pill, or roll back + notify on failure.

Where

mobile/src/lib/sessionManager.ts (sendMode, ~408–414).

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Filed from a UI research sweep of the Helm mobile app (landing + live demo session) using Playwright + full source review, cross-referenced against Claude, ChatGPT, GitHub Copilot Chat, and Codex/Claude Code UIs.

[aasis21]

Fixed on \main\ in commit 4262060 as part of the P1 UI sweep (wave 1). This issue was implemented but not auto-closed because GitHub only honors the closing keyword before the first issue in a multi-issue \Closes\ line.