The case reproduces an overlap — the render deadline expiring while the
survival window is still open — and it had to buy that overlap with a
startup allowance. `paintAt` is measured from the child's first JS tick
while `renderTimer` is armed in the parent at spawn, so a plain
`setTimeout(paint, N)` lands at `N + startup` and the deadline has to
cover whatever startup turns out to be. #2177 widened that allowance
(150ms to 950ms), which moves the threshold rather than removing it: the
case still fails, as "did not render", on any machine loaded enough to
blow the new number.
The child is now told the wall-clock instant to paint at and sleeps for
whatever is left of it on arrival, so startup is absorbed by the sleep
instead of added to it and the paint lands at ~300ms from spawn however
slow the boot was. `timeoutMs: 600` / `surviveMs: 900` then satisfies
the right-hand side of the overlap for ANY paint time including 0, so a
boot slow enough to swallow the anchor entirely still reproduces the
shape rather than degrading into a different case. The one startup
assumption left is that boot completes before the deadline at all, an
order of magnitude over the 46-59ms measured idle here.
Passing is no longer taken as evidence on its own: the verdict's
first-paint time is read back and the overlap asserted, so a paint
landing early enough to put the deadline outside the survival window
fails loudly instead of passing while testing nothing.
Verified by mutation — removing the `clearTimeout(renderTimer)` this
case guards fails it at 607ms, i.e. the timer still fires inside the
survival window. Verified under load — 8/8 with 16 busy loops pinning
all 8 cores. Runtime drops from ~1.75s to ~1.2s.
Closes#2180
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013hzwzS8UvBsr4yZm7o7sev
Signed-off-by: cliffhall <cliff@futurescale.com>
2e4e76aa1a