vgsp-gr r556: absolute 15 s per-launch deferral cap (single stall backstop)

r553/r555 boots still show clients walking the individual defer/hold
bounds for 400+ s: victory_reduce 430 s (same push VA re-deferred every
pass, r554's 64-slot latch), victory_saxpy 254 s at write time with
work_guard deferred climbing by the thousand. Each guard is bounded on
its own, but their bounds interact and re-arm across re-decode passes.

Arm an ABSOLUTE per-push-VA deadline on first sighting (64-slot table);
once 15 s have passed, svc_gr_defer_expired() returns true and every defer
site forwards best-effort: the r541 dstpend guard, the r543 arg-partial
guard and the m150 data-stalled hold. 15 s sits far above the 0.5-2 s pin
latency the deferrals exist to cover and far below every client-side
timeout (>= 60 s), so the pin-late cases keep their window and no launch
can be parked longer than the cap, whichever guard keeps winning.

0 files changed, 0 insertions, 0 deletions