v0.6.1

Fixed

• Fixed running cancellation so it terminates the remote command process group instead of relying on local SSH transport teardown.
• Replaced shell-builtin negative-PID process-group signalling with explicit python3 os.killpg() calls to avoid /bin/sh portability ambiguity.
• Added a per-job remote /tmp/exec-mcp-runtime/<exec_id> cancellation handshake and remote_exit_confirmed reporting; unconfirmed remote termination now finalizes as failed with failure_reason=remote_termination_unconfirmed.
• Updated the fake SSH harness to isolate the simulated remote shell from the local transport process group, preventing false-positive cancellation tests.
• Added a regression test matching the live failure mode where a cancelled background (sleep; touch marker) process previously survived.