Adds a docker-compose service `server-spool` that runs secs_server
with --spool-dir pointed at a named volume. Two-phase Python
harness (interop/spool_persistence_test.py):
1. Enqueue phase: force-spool one S6F11(CEID=300) via the
SPOOL_ON / START / SPOOL_OFF RCMD trio, then disconnect.
2. Driver runs `docker compose restart server-spool` between
the phases — the named volume preserves the journal files.
3. Drain phase: reconnect, send S6F23(Transmit), verify the
replayed S6F11 carries CEID 300.
Surfaces a real interop bug along the way: secsgem-py 0.3.0 encodes
RSDC (and other "single-byte status" fields) as <U1>, while SEMI E5
spells them as <B>. Our `as_binary_first` was strict on Binary; now
accepts either (the byte semantics are identical, and the leniency is
symmetric with the U-type widening from the first interop commit).
Result: enqueue → docker restart → drain returns CEID 300 cleanly.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
