worker: count a session as productive only if the pool sent a job

PoolParticipantMiner returned true from its normal cleanup path whether or
not the pool had ever sent work, so a pool that completed the tunnel and
then dropped was indistinguishable from a healthy one. The caller reset
nRetrySecs to 10 on every such "session", pinning the reconnect at a flat
10s and defeating the backoff in precisely the case it was added for. It
cleared nFailingSince as well, so the "failing for N minutes" line never
printed either -- the worker went back to idling silently.

Return true only once at least one well-formed mining.notify has arrived.
The existing early returns are unaffected: they already mean "no session",
which stays the right answer for any path that leaves the worker without
work, a failed hash-thread spawn included.

0 files changed, 0 insertions, 0 deletions