Wire the pure sweatbox engine to FSD sessions with dual bookkeeping:
claim before Register, post-Register commit check, abortFailedAdd vs
cleanupSyntheticSession, AfterFunc pointer-scoped only (stopAF before
Cancel on intentional Remove), engine.Delete only if owned.
Also: FPL encode goldens, PackPBH round-trip, kick/$!! Remove for
Synthetic, SWEATBOX_ENABLED default false (TestServer true), tick apply
with map + same-pointer Find, State merges session FlightPlan.