Pending message lost when leaving a chat (non-terminal client)

When using Claude Code from a client other than the server-side terminal console (e.g. the web/app chat interface), sending a message to an in-progress chat leaves it stuck as "pending" -- it never gets delivered while the chat stays open.

If you leave the chat at that point, the pending message is lost entirely.

Current workaround: leave the chat and re-enter it, then send the message again -- only then does it get received.

This makes it unreliable to send follow-up messages to a running session from a non-terminal client.