Scheduler.deinit closes the bounded leaks B1 documented: it reaps any leftover
ready fibers, frees every heap Task from go (now tracked via a task_allocs
field), frees the timers/io_waiters/task_allocs List backings, and closes the
lazily-opened kqueue fd. Terminal + idempotent; the per-spawn/go closure env
remains unfreeable (language limitation). Locked by
examples/concurrency/1820-concurrency-fiber-scheduler-deinit.sx, which exercises
every freed resource under a tracking GPA (freed by deinit: 5, kq reset to -1).
Also converts plain-struct '= ---'+field-assign init to '.{ ... }' literal init
where '---' carries no meaning: Scheduler.init, Dock.make, and the fiber
examples 1811/1813/1814/1816 (partial literals zero-fill the index-filled array
fields). Unions, '---'-feature tests, the 0154 regression, documented
generic-pack gaps, and loop/conditional inits are intentionally left on '---'.
library/modules/std/sched.sx: a generic Fiber + Scheduler over the
proven naked swap_context on guarded mmap stacks --
init/spawn/yield_now/suspend_self/wake/run (B1.5a), then Task($R) +
go/wait/cancel, a truly-suspending nullary-thunk async layer (B1.4a).
go(work) runs a thunk as a real fiber; wait() parks the caller until it
completes. Self-contained in sched.sx (io.sx importing it would
duplicate the _fib_tramp global asm).
Hardened per adversarial review: wake guarded on .suspended (FIFO
corruption), suspend_self/yield_now guard a null current, loud
mmap/mprotect/OOM/deadlock bails, cancel skips not-yet-run work.
Closure-env + heap-Task leaks documented (bounded, default-GPA-invisible).
Examples: 1811 (round-robin), 1812 (suspend/wake + spurious-wake guard),
1813 (async interleave + await-suspend + cancel). Also files issue 0155
(scalar-pointer index panics codegen -- non-blocking, found in review).
