bug(cli): stale Claude terminal frame remains after exit on Linux #175

What happened

After exiting Claude Code through Blue with /exit, the shell prompt appears at the top of the terminal while stale Claude output and its input UI remain below it. Expected: a coherent shell display after the agent exits, without the prompt overlapping the previous TUI frame.

Observed repeatedly during local testing. In one capture, the first lines after exit were:

user@blocks:~/workspace/blue/scratch$
Resume this session with:onfig file > full.
claude --resume 7e16ce43-bbab-4c95-ae62-874e953a8d59

Possible cause: the supervisor's normal child-exit path clears only the footer, then TerminalModeGuard leaves the alternate screen. The additional full primary-screen clear is Windows-only. This is a code-inspection hypothesis, not a confirmed root cause; direct Claude versus Blue has not yet been isolated.

Relevant code: normal exit, terminal reset.

Separate from the startup-logo overlap fixed by #164. The exit issue was reproduced with the released v0.2.0 client; it has not been retested with a client built from current main.

Steps to reproduce

1. Connect Blue to a local Docker Compose deployment and sign in.
2. Run blue claude with Claude Code 2.1.252 in a desktop terminal attached to tmux.
3. Send a prompt and wait for its response.
4. Enter /exit.
5. Observe the shell prompt at the top of the terminal with the previous Claude frame still visible beneath it. Repeated launches/exits make the stale display especially apparent.

The tested deployment had gateway mode and session capture enabled; capture completed successfully despite the display issue.

Blue version

Blue metaharness 0.2.0 — released Linux x86_64 musl CLI (v0.2.0 / b04ca3e). Backend built from main at 1a538aa.

OS / environment

Ubuntu 22.04, Linux 6.1.158+, XFCE desktop terminal attached to tmux 3.5a; client terminal xterm-256color, pane 160×44. Claude Code 2.1.252.