The scheduler's pre-dispatch loop called advance_next_run per due job —
one full load_jobs() + one full save_jobs() of the jobs file each — so
N due jobs cost N reads + N writes of the whole file (gateway-restart
catch-up or co-scheduled bursts). advance_next_runs() does one load +
at most one save for the whole due set with identical per-job semantics;
advance_next_run() is now a thin wrapper over it.
Measured (50 due recurring jobs, real jobs file): 107.9 ms -> 2.5 ms
(45x; 50 loads + 50 saves -> 1 + 1).
Tests: batch advances recurring and skips one-shots, single load + save
I/O pin (fails pre-fix — no such function), no save when nothing
advances, and per-job wrapper semantics unchanged. Related: #60946 and
#75833 both restructure this loop's call site for correctness — neither
addresses the I/O cost, and this batch primitive composes with either
dispatch design; happy to rebase onto whichever lands first.
spfcraze
947310437b