- Add MsgConnectionRefusedException to distinguish ECONNREFUSED from other
connection errors; openConnection() now throws it when connect() returns
ECONNREFUSED.
- MsgClient::call() adds retry_on_refused/retry_interval parameters (defaults
false/1.0s), matching Python pymsg.MsgClient.call(retry_on_refused=True).
- Retry loop: only retries on ECONNREFUSED; other exceptions (timeout,
connection reset, business errors) propagate immediately. Throttled logging:
first failure prints immediately, subsequent logs every 5 seconds.
- DbC::call_msg() enables retry_on_refused=true (db is a hard dependency;
gateway blocks waiting for db on startup instead of crashing).
- LogC::_send() explicitly passes retry_on_refused=false (fail-safe; never
block the background log thread when db is unavailable).
- captcha/smtp auxiliary services keep default retry_on_refused=false
(fail-fast; blocking in request threads would exhaust the thread pool).
- Update README with pymsg protocol documentation, downstream retry strategy
table, and v0.6.1 changelog entry.
qing