Flowgraphs generated by GRC on the host often fail in Docker containers
due to three issues:
1. message_debug constructor signature changed between GR 3.10.5 and
3.10.12 — strip the second arg for older runtimes
2. XML-RPC binds to localhost, unreachable from Docker host — rewrite
to 0.0.0.0
3. input('Press Enter to quit:') gets immediate EOF in detached
containers, killing the flowgraph instantly — inject signal.pause()
fallback after EOFError
All patches are applied in a single pass via patch_flowgraph() before
the container launches. The original file is never modified.