fibers: end-to-end M:1 capstone (B1.5) — Stream B1 complete

1817 composes the whole colorblind pure-sx async stack: the M:1
scheduler, suspending go/wait async, and deterministic virtual-time
sleep/now_ms, over the naked swap_context on guarded mmap stacks. A
coordinator launches three async tasks (sleep 30/10/20 -> return
100/20/3), awaits all three in spawn order, and sums them; tasks
complete in DEADLINE order (task 2@10, 3@20, 1@30), sum 123, final
virtual clock 30 -- fully deterministic.

Stream B1 (fibers + Io + M:1 scheduler) is feature-complete: examples
1800-1817, suite 755/0. Checkpoint + plan marked COMPLETE; next carve
is Stream B2 (channels / cancel / async stdlib).

current/PLAN-FIBERS.md

@@ -1,6 +1,14 @@
 # PLAN-FIBERS — Stream B1 (fibers + Io + M:1 scheduler)
 
-> **STATUS: 🚧 in progress.** B1.0 (`abi(.naked)`) ✅ · B1.1 (per-fiber `context`) ✅ · B1.2
+> **STATUS: ✅ COMPLETE.** The pure-sx M:1 async runtime is feature-complete end-to-end
+> (`library/modules/std/sched.sx`, examples 1800–1817, suite 755/0): `abi(.naked)` context switch
+> (aarch64 + x86_64/Win64), M:1 scheduler, suspending `go`/`wait`/`cancel`, deterministic virtual-time
+> timers (`sleep`/`now_ms`), and real fd readiness via kqueue (`block_on_fd`). Five compiler bugs fixed
+> en route (0151/0152/0153/0154/0156-P1/0157). Deferred non-blocking follow-ups: linux `epoll` twin,
+> `Scheduler.deinit`, `Future(void)`/`timeout` (0150), `context.io`-routed async (M:N). Next carve:
+> Stream B2 (channels / cancel / async stdlib). Historical step-status below.
+>
+> B1.0 (`abi(.naked)`) ✅ · B1.1 (per-fiber `context`) ✅ · B1.2
 > (`Io` interface + `async`/`await`/`cancel` over blocking `CBlockingIo`) ✅ · B1.3 (fiber
 > runtime: naked `swap_context` + §10.7 stress gate + guarded `mmap` stacks, proven on aarch64
 > AND x86_64/Win64) ✅ · **B1.5a (M:1 scheduler CORE — `std/sched.sx`: `spawn`/`yield_now`/
@@ -9,7 +17,7 @@
 > blockers 0156-Part1 + 0157 en route; locked `1813`).
 > **B1.4b (deterministic virtual-time timers — sched.sleep/now_ms/timer-run) ✅** (reviewed; fixed a CRITICAL timer-vs-early-wake UAF; locked 1814/1815).
 > **B1.4c (event-loop — real fd readiness via kqueue: `block_on_fd` + run-loop Mode 2) ✅** (reviewed; fixed a CRITICAL same-fd lost-wakeup hang; locked 1816). macOS only — linux epoll twin deferred.
-> **→ NOW: B1.5** — end-to-end M:1 validation under the deterministic timers / fd readiness. Detailed progress in [CHECKPOINT-FIBERS.md](CHECKPOINT-FIBERS.md). NOTE: suspending async +
+> **B1.5 (end-to-end M:1 capstone — `go`/`wait`+`sleep`+scheduler, deterministic ordering) ✅** (locked 1817). **STREAM B1 COMPLETE.** Detailed progress in [CHECKPOINT-FIBERS.md](CHECKPOINT-FIBERS.md). NOTE: suspending async +
 > deterministic timers live as `sched.*` methods (M:1), NOT routed through the erased `context.io` (avoids forcing sched.sx into every std consumer + the `_fib_tramp` dup-symbol
 > trap); the `Io` protocol's `spawn_raw`/`suspend_raw`/`ready` stay reserved for M:N. Deferred:
 > issue 0150 (`Future(void)`/`timeout`); 0156-Part2 (deferred `..` spread); the `::` callable-param
@@ -223,9 +231,11 @@ Blocking exists (io.sx `CBlockingIo`). Next the deterministic-sim `Io`, **calibr
 blocking** before any `18xx` test trusts it; then the event loop. The deterministic `Io` is the
 test harness for *all* of B1.5 + Stream B2.
 
-### B1.5 — A5: M:1 scheduler
-End-to-end validation of the colorblind stack. `18xx` corpus under the deterministic `Io`,
-asserting program-emitted ordering contracts.
+### B1.5 — A5: M:1 scheduler — ✅ COMPLETE
+End-to-end validation of the colorblind stack. The `18xx` corpus asserts program-emitted ordering
+contracts under the scheduler + deterministic timers; the capstone `1817` composes `go`/`wait` +
+`sleep`/`now_ms` + the scheduler (three tasks complete in deadline order, deterministic sum). Stream
+B1 is feature-complete.
 
 ---