The TUI was calling archive_proposal for gitleaks-allow immediately
after write_response, moving the response file to processed/ within
microseconds. The git-gate shell loop polls queue_dir for the response
file every second — it never sees it and hangs until timeout.
capability-block is handled by the MCP sidecar which archives after
reading; gitleaks-allow is handled by the shell gate which archives
after processing. Let the gate own the archive step.