rerun cycle 18 rather than reconstruct it

The async/future measurements were produced by a C stub in /tmp, and that
artifact was destroyed when the session worktrees were removed. The log then
asserted results with nothing behind them -- a claim inside an evidence record,
which is exactly what turns a chain of custody into a pile.

Rerun, not reconstructed. Rebuilding the missing file would have been a
fabrication with a fresh timestamp; rerunning produces new evidence with its own.

  lang/tests/integration/fixtures/future.c   the future, as a tagged heap object
  lang/tests/integration/async_future.sh     the harness, 6/6

  ok  unbound: synchronous, correct result
  ok  unbound: el_await on a non-future passes through, no crash
  ok  bound: does not crash
  ok  bound: the awaited result is correct
  ok  bound: the caller continues BEFORE the body finishes
  ok  bound: wrap returns in <10ms while the body takes 50ms

LABELLED AS A REPLICATION. The outcomes were already known when this harness was
written, so its expectations are NOT predictions committed in advance. Its
evidentiary value is that a third party can reproduce it, not that it was called
ahead of time. Recording it as anything stronger would corrupt the record it is
meant to repair.

The fixture also carries the P5 defect and its fix in a comment: the first
el_await dereferenced ->magic off an unvalidated slot and SIGSEGV'd on the
unbound path, sixty seconds after the same defect was diagnosed elsewhere in the
runtime.

docs/v1/experiments/cycles/18-async-half-expressible.md

@@ -1,6 +1,21 @@
 # async — half expressible, and the cycle that was dogma
 
-**Status: measured on a branch, not merged. Two runs — the first was invalid.**
+**Status: replicated and corroborated. Three runs — the first was invalid.**
+
+> **Chain of custody note, 2026-08-17.** The original measurements were produced
+> by a C stub written in `/tmp`, and that artifact was destroyed when the session
+> worktrees were removed. For a period this file asserted results with nothing
+> behind them — a claim inside an evidence record, which is the defect that turns
+> a chain into a pile. It was **rerun**, not reconstructed: reconstructing the
+> missing file would have been a fabrication with a fresh timestamp.
+>
+> The fixture now lives at `lang/tests/integration/fixtures/future.c` and the
+> harness at `lang/tests/integration/async_future.sh`, so a third party can
+> reproduce this without taking my word for it. **6/6.**
+>
+> The replication is labelled as such: the outcomes were already known when the
+> harness was written, so its expectations are not predictions committed in
+> advance. Its value is reproducibility, not foresight.
 
 ## The first attempt was DOGMA, not science