Adopts the KPN backpressure fix (28e0667) and registers the application
error listener it exposes.
`push_blocking` parked a scheduler worker inside the push. Each ObjectNode
owns a private single-thread pool, so the parked thread was the only one
that could drain that node's own input: under sustained backpressure
frame_source, camera_pos, face_detector and face_aligner all slept in
nanosleep at once and the pipeline stopped. Nodes now hold the value,
release the worker, and resume on a channel space-callback.
main.cpp registers set_error_handler so a node that throws names itself
and its exception. Previously the exception was discarded at the node
boundary and survived only as "node 'x' stopped unexpectedly", which says
that a node died but not why — the missing detail that made this slow to
diagnose.
AR-004 drops from Done to Mostly. Two gaps are recorded rather than
claimed fixed: a hang surviving at roughly 1 run in 20 against a 300 s
timeout (down from every run failing), and FanoutNode still dropping on
overflow instead of parking, which sheds frames on the AR-010 scene join
precisely when the dense branch falls behind.
TRACES: AR-004 | SR-002
dtourolle
5c6603e63b