Files
booth/persistent-memory.d/2026-09-23-the-browser-suite-is-flaky-under-load.md
T

59 lines
2.8 KiB
Markdown
Raw Blame History

This file contains ambiguous Unicode characters
This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.
# The browser suite is flaky under load — UNRESOLVED, and owned by design-dev
_2026-09-23 · booth_
⚠ **OPEN. Not fixed. Do not read a green suite as proof of anything without
re-running it.**
## What is observed, with its limits
**Three different browser tests** have each failed once under full-suite load
while passing repeatedly in isolation:
| test | owner | isolation | full suite |
|---|---|---|---|
| `test_the_keyboard_flag_actually_submits` | booth-dev | 5/5 pass | 1 failure |
| `test_a_failed_save_says_so_reloads_and_never_re_posts` | design-dev | 3/3 pass | 1 failure |
| `test_the_review_keys_judge_in_place_and_stay_out_of_the_note` | design-dev | 10/10 + 5/5 pass | 1 in ~9 |
Three different tests points at **the environment under contention**, not at any
one test. That is a direction, not a finding.
## Two real defects found chasing it — NEITHER PROVEN TO BE THE CAUSE
1. **A keypress race.** The flag test fired `ArrowRight` and `f` back to back,
assuming the first had finished — but `focus()` does a `scrollIntoView`, so
under load `f` could arrive with no cursor set. Now waits for
`figure.item.is-cursor`.
2. **A port TOCTOU in BOTH browser fixtures.** Each did `bind → getsockname →
CLOSE → hand uvicorn the port NUMBER`, leaving a window for the kernel to
give that port away — and this suite runs two browser files that each start a
server per test, so the competitor is the other file. The bound socket is now
passed to `server.run(sockets=[sock])`.
**Since those fixes: one failure in three full runs. n=3 CANNOT distinguish
that from the prior rate, and no claim of improvement is made.**
## Who owns it and what the method is
**The operator ruled: "let him diagnose it properly."** design-dev owns it. His
method: a trace hook keeping a Playwright trace (screenshots + DOM snapshots)
for every browser test that fails, captured **from the run that fails**, then
full-suite runs until red and the artefact decides. Test-only infra, on his
branch as its own commit.
⚠ **The methodological trap, and why the artefact must come from the full
suite:** the failure only reproduces there. A narrowed repro that passes proves
nothing and will be mistaken for a fix.
## Addendum 2026-09-24 — the offline fix, and what 0/24 can and cannot say
design-dev's suspect was Google Fonts stalling "networkidle". A stalled font
request reproduces the exact error (which shows sufficiency only). The fix
landed in `b92b002`: the test browser has no internet, with a positive control
per fixture. Traced runs: 0/15 (light) and 0/8 (heavy). No trace ever caught
the stalled request. Untraced after the fix: **0 reds in 24**, against a pre-fix
rate of 1 in 8 that is itself one red in eight runs (95% CI roughly 0.3–53%).
At a true rate of 1 in 20, 0/24 happens 29% of the time. So it's consistent
with the fix and not a confirmation of the cause.