fix(ci): nextest had no per-test timeout — the key name was wrong, so a hang killed the job anonymously and evicted the merge queue

[noahgift]

main has not moved all day. This is why.

The defect

[profile.ci]
slow-warning = "60s"

There is no slow-warning key in nextest. The real one is slow-timeout. nextest does not reject an unknown key — it prints a warning and carries on:

warning: in config file .config/nextest.toml, ignoring unknown
         configuration key: profile.ci.slow-warning

So profile.ci had no per-test timeout at all. From merge_group job 95162862834 for #2502:

12:31:55  build starts
12:50:58  Starting 80806 tests across 69 binaries
13:36:07  ##[error]The operation was canceled.

45 minutes inside nextest, killed by the job's timeout-minutes: 85, naming no test. #2502 was evicted from the merge queue 31 seconds later.

That warning was line 353 of that job's log — and of every workspace-test log before it.

The compounding half

status-level = "fail" is below slow in nextest's ordering (none < fail < retry < slow < pass < all), so the SLOW lines that would have named the culprit were suppressed too. Measured on a probe crate:

status-level	SLOW lines
fail (current)	0
slow	3

Fixing the timeout without this would have kept hiding the warning that precedes the kill.

terminate-after is measured, not guessed

Full workspace run on an idle 48-core box — 80,806 tests, 353s wall:

test	duration
aprender-orchestrate bug_hunter::test_bh_mod_001_hunt_all_modes	202.7s
aprender-orchestrate bug_hunter::test_bh_mod_001_hunt_returns_result	157.3s
aprender-orchestrate bug_hunter::test_bh_mod_046_apply_spec_quality_gate_no_pmat	118.0s
aprender-train transformer_trainer::falsify_lora_tests::…rslora_stable_high_rank	67.5s

over 60s: 6 · over 120s: 2 · over 300s: 0

terminate-after = 20 periods = 1200s is ~6× the slowest real test, so it cannot kill a legitimately slow one — while a genuine hang dies at 20 minutes with a name instead of taking the whole job down anonymously.

(The bug_hunter tests are separately being made fast; this bound does not depend on that landing.)

Also fixed

• timeout-minutes: 85 → 100. The step sets 75, but "Set up runner" measured 20 minutes, so 20 + 75 = 95 > 85 and the job timeout always fired first — producing a bare "The operation was canceled" naming no step. The step timeout must be the one that can fire, because it points at the step.
• junit path was doubled. path is relative to the store dir, not the workspace root, so target/nextest/ci/junit.xml produced target/nextest/ci/target/nextest/ci/junit.xml. Now junit.xml, verified landing at target/nextest/ci/junit.xml.

Guarded

A warning nobody reads is not a diagnostic, so it is a hard failure now. check_nextest_config_keys.sh runs nextest's real parser against a three-line throwaway crate with this repo's config — no regex of my own guessing at nextest's schema — and fails on any ignored key. Its case table carries a control row so it cannot pass by reporting every key it sees.

Mutation: restoring slow-warning turns it RED; restoring slow-timeout turns it green. Verified both directions.

Wired into guard-runner-labels, which is in gate.needs. bashrs lint: 0 errors.

Refs #2502

[noahgift]

Superseded by #2527, which consolidates this with the other guard PRs. All four inserted into the same guard-runner-labels block in ci.yml, so merging them separately meant one conflict per merge — and each rebase is another push competing with the merge queue. Resolved once in #2527; the commits are carried over unchanged.