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What is wrong

test/test_nilpy_class_named_like_an_rtl_record.npy writes, re-reads and then deletes a probe file at a fixed absolute path:

line 51:  f = open("/tmp/pxx_nilpy_rtlrec_probe.txt", "w")
line 56:  g = open("/tmp/pxx_nilpy_rtlrec_probe.txt", "r")
line 63:  os.remove("/tmp/pxx_nilpy_rtlrec_probe.txt")

The path is chosen at runtime, by the compiled program. That is what makes it different from a fixed path in a Makefile recipe: the Makefile sweep never sees it, and testmgr's per-run privatization has nothing to rewrite. Every run of this test on a box, from any clone, uses the identical file.

Why it matters here specifically

This is not a theoretical race. Several clones' testmgr run concurrently on plexus as a matter of course — an opt sweep this session recorded NOTE this run shared the box with another clone's testmgr and named two other clones. With two runs overlapping:

The failure is intermittent and blames the wrong thing: it surfaces as a NilPy class/RTL-record assertion failing, not as a file-sharing problem, and it only appears when the box is busy. That is the expensive shape — a flaky red whose message points away from its cause.

How the guard found it

tools/testmgr_hardcoded_tmp_devtest.py exists for exactly this class and is RED on master today:

FAIL: new hardcoded /tmp path(s) in compiled test sources. These are written at RUNTIME, so no Makefile sweep reaches them and testmgr cannot privatize them — two concurrent runs share the file.

It is one of the 89 guards in tools-devtest, so the job is red for this alone (88 green, 1 red).

The fix

The devtest states both accepted forms:

No sibling .npy test currently reads TESTTMP, so whoever takes this sets the pattern for the rest of the NilPy suite.

Boundaries

2026-09-20 — the cited instance was fixed; the mechanism recurred twice (frankz-e5)

The summary above was rewritten today and this note records why, because the failure is one CLAUDE.md names and this is a dated instance of it.

test_nilpy_class_named_like_an_rtl_record.npy:38 now reads ... or "/tmp") + "/pxx_nilpy_rtlrec_probe.txt" — the env chain, correctly. It was fixed at some point after 2026-08-28 and the summary went on naming it as the live offender, so a seat dispatched to this p45 would have opened a correct file and reasonably concluded the ticket was done.

Measured 2026-09-20 at 0ae279ae9, make tools-devtest, job's own verdict 163 green, 2 RED over 165 of the 166 files tools/*devtest*.py globs:

test/test_nilpy_io_open_in_a_module_that_rebound_open.npy   /tmp/test_nilpy_io_open.txt
test/test_nilpy_mmap_read_only_and_struct_unpack_from.npy   /tmp/pxx_test_mmap_read_only.bin

Why nobody noticed for 23 days, and it is not inattention. This guard reports through tools-devtest, which is an AGGREGATE reporting under the opaque shard tools-devtest#00. That job has been continuously red since 2026-09-12 (new_red at e115014ceb5e, then 182 consecutive still_red through 09-20, zero transitions). A saturated aggregate cannot report a new red inside it — so this recurrence, an unwired-test omission on 09-14 and a binary-name collision on 09-16 all landed into one unchanging level. Written up in devdocs/dev/debugging-playbook.md, "AN AGGREGATE JOB SATURATES".

The remedy the guard itself prints is the env chain, in Pascal, C and NilPy spellings. Nothing here needs designing.

2026-09-20 — fixed, and the remedy this ticket prescribed was HALF WRONG (frankS)

35841d247. tools/testmgr_hardcoded_tmp_devtest.py rc=1 -> rc=0, and make tools-devtest now prints its own verdict as 165 guard(s) green — no red, so the saturation this ticket predicted and priced is over.

THREE files, not the two measured on 09-20. The third is not a .npy and that is why two censuses in a row missed it:

test/test_nilpy_io_open_in_a_module_that_rebound_open.npy   /tmp/test_nilpy_io_open.txt
test/test_nilpy_mmap_read_only_and_struct_unpack_from.npy   /tmp/pxx_test_mmap_read_only.bin
test/lib_findfirst.pas                                      /tmp/pxx_lib_findfirst_sandbox

The guard globs compiled test SOURCES, which is every frontend; the readers kept summarising it as a NilPy problem because the first instance and the recurrence both happened to be .npy. The mechanism is frontend-neutral.

THE ENV CHAIN IN "The fix" ABOVE IS THE DEFECT WEARING A FIX. That section says to read $TESTTMP, "which the sweep already exports". It does, to a make recipe — and not to a testmgr job, which is the run that actually races. testmgr launches jobs through an env allowlist (ENV_ALLOW / ENV_ALLOW_PREFIXES = PXX_ TESTMGR_ LC_ QEMU_), and TESTTMP matches no prefix in it. A test that consults TESTTMP alone gets nothing under testmgr and falls through to /tmp — passing this guard, in the wanted form, still racing. The order must be

TESTMGR_TMP  ->  TESTTMP  ->  /tmp

with TESTMGR_TMP FIRST because it is the only one that survives into a job. All three files now take it in that order.

Positive control that the env arm is READ and not merely present, since a chain whose first two arms are dead is indistinguishable from a correct one on a box where /tmp happens to be free: TESTMGR_TMP=/nonexistent-franks-probe gives PRECONDITION FAILED: no sandbox at /nonexistent-franks-probe/pxx_lib_findfirst_sandbox and total ok 0 / 1. With the env unset, 44/44; with an explicit argument, 44/44; both .npy MATCH their .expected.

What should retire the guard, not just this ticket: the guard cannot see a test that reads TESTTMP only, because that IS its prescribed remedy. A test written to the letter of the advice above passes and still races under testmgr. Teaching it to require TESTMGR_TMP first is a Track T change and is not filed — say so before quoting a green from it.

Log

2026-09-20 — CORRECTION, same day, same seat: the gap I just described is CLOSED, and I said so while holding the file that closes it (frankS)

The note above ends "Teaching it to require TESTMGR_TMP first is a Track T change and is not filed." Both halves are false.

It is BUILT. tools/testmgr_hardcoded_tmp_devtest.py carries a SECOND check — ENV_READ_RE, KNOWN_ENV_ONLY — whose header block states the allowlist argument in the same terms I wrote it in, and it enforces the ORDER, not merely the presence. Positive control, run before writing this: a scratch Pascal file under test/ reading GetEnvironmentVariable('TESTTMP') with no TESTMGR_TMP arm makes it exit 1 and name the file; removing the file returns it to 0. Five files are grandfathered in KNOWN_ENV_ONLY with their owning lane named, so it is a ratchet exactly like KNOWN.

And it is FILED, and closed: devdocs/progress/done/bug-t-the-hardcoded-tmp-guard-recommends-a-variable-testmgr-strips.md, cited by name in the guard's own comment block four lines above the regex.

What produced the error is worth more than the error. I derived the allowlist fact correctly, from testmgr, and then narrated it as a discovery instead of grepping for whoever had it first — within an hour of telling frankz-e5 that the lesson from their own correction was to grep for whoever already called the hazard, and to attach evidence to their ticket rather than write a new page. Same failure, one layer in, in the text arguing for the remedy. The tell was available and I read past it: the guard PRINTS the ordered chain with the allowlist reasoning attached, and I quoted that output in this session while calling the check absent.

So the sentence to distrust is not the measurement — the measurement was right — it is "and nobody has built this", a quantifier over a population I never enumerated, arriving at the end of a paragraph whose earlier clauses were all verified. CLAUDE.md names exactly this ("THE CLAUSE TO GO MEASURE IS THE QUANTIFIER"); the checked half lent its credibility to the unchecked half.