`--continue` exits non-zero when an agent has been spun up but
never typed at — there's no transcript to resume. Re-attaching
to such an agent via Enter (tmux mode) was crashing the pane.
Wrap the resume invocation in `sh -c '<cmd> --continue || <cmd>'`
so a failed `--continue` cleanly falls through to a fresh
claude. The shell adds microseconds and the fallback only
kicks in when --continue would have failed anyway.
New `_build_resume_argv_with_fallback(bottle)` builds the
shell-wrapped docker exec argv with proper shlex quoting (so
paths-with-spaces in `--append-system-prompt-file` survive).
Only the tmux re-attach path uses it; first-attach + foreground
handoff are unchanged.
489 unit tests pass (4 new for the fallback builder).
didericis
1a1ba6abd5