sema: r408 acquire-wait gate defaults ON (the r408 streams2d readback race) + explicit param desc

With the gate off (the mission cycle recipe omitted sema_wait_gate=1),
the c2 readback's C56F ACQ_CIRC_GEQ pay=4 ran at 106617.279 with cur=2 -
before the c2-add launch was even submitted (106617.411) - and read the
not-yet-produced buffer (all zeros). With the gate on the same readback
holds until the scale channel's progress counter reaches 4 (sema-wait:
hold ... cur=2 waited_ms=353 -> pass ... cur=4) and the ordering is
correct. The holds are bounded (sema_wait_hold_ms, default 4000) and
fail open loudly, so the pre-r336 pass-through remains available with
sema_wait_gate=0 for an A/B.

0 files changed, 0 insertions, 0 deletions