Chat message silently dropped when switching desktop -> phone client during 'preflight' send phase

Summary

A chat message that is in the "preflight" send phase on the desktop client is silently dropped if the user switches to the phone client before preflight completes. The message never reaches the assistant, never appears in the conversation on either client, and the user receives no failure indication.

Environment

• Desktop client: Claude Code
• Mobile client: Claude Code on phone (same account / same session)
• Cross-client session handoff: desktop -> mobile

Steps to reproduce

1. Type a chat message in Claude Code on the desktop client.
2. Submit the message so it enters the "preflight" send phase (visual indicator shown before the message is fully transmitted to the API).
3. Before preflight completes, switch to the phone client and resume the same session.
4. Observe the conversation on the phone client.

Actual behavior

• The message does not appear in the conversation on the phone client.
• The assistant never receives the message (no response, no record of it in subsequent turns).
• No "send failed" or "message not delivered" indicator is shown on either client.
• The user believed the message had sent and only discovered the loss when the assistant's next response showed no awareness of it. The message had to be retyped.

Expected behavior

One of:

• (a) The message in preflight finishes sending and appears in the conversation regardless of which client view is active when send completes, or
• (b) A clear "send failed / message not delivered" indicator is surfaced on the phone client (and/or desktop on next focus) when the session resumes and the preflight buffer was not flushed.

Silent drop is the worst outcome and should not occur in either case.

Suspected scope

Cross-client session handoff during the pre-send window. The preflight buffer appears to be desktop-client-local and is not flushed or synced before the session lock transfers to the mobile client. When the mobile client takes over the session, the in-flight message in the desktop's preflight buffer is orphaned and discarded with no error surfaced to the user.

Impact

• Silent data loss of user input.
• User trust erosion: the user thought the message had sent.
• Forces retyping and disrupts conversation flow, particularly painful for longer messages composed on desktop before moving to mobile.

Reporter

• Joshua Danford (joshua.danford@gmail.com)
• Date observed: 2026-05-12