The session's Markdown actions registered BackHandler natively only, so on
the page an unsaved draft left the key unclaimed and the shell's pop dropped
the edits without the prompt. The hook now claims through useBackClaim on
both platforms: always natively, where leaveSession replaces to the host at
the root instead of exiting the app, and on the page only while a draft is
dirty, since an unclaimed press there is already the shell's own leave.
Claude-Session: https://claude.ai/code/session_01JNnE9qzUZMMnqpZWCqM3nb