Token string marking the PERP (futures) ledger row in get_balance
output. Under the manual-account model spot and futures are SEPARATE
ledgers; the futures row is appended LAST and carries __PERP__ so
consumers can split the two without positional fragility.
Marker sent to all subscribers when the manager tears the connection down
for a RECONNECT (transport reset / idle watchdog / stream end). Consumers
MUST treat this as “a reconnect is happening, subscriptions will be
replayed” — NOT a per-stream error; the manager logs the cause once at
warn and the loop replays all subscriptions on the fresh connection.
Mirrors the SHUTDOWN_MARKER pattern in core/src/orderbook/sync.rs.
True when an error string is a transport-level reconnect marker rather
than a per-stream failure. Consumers use this to downgrade logging
(debug) vs genuine stream errors (warn).