fix(ci): make the cluster-global serial group actually group

[jason931225]

Independent of #814/#815 — touches only .config/nextest.toml and its gate.

The defect

The serial minority was filtered with test(/name/), but every name in that list is a test binary name and test() matches test names. The group captured only tests whose own name happened to contain the binary name.

Measured with cargo nextest show-config test-groups (cargo-nextest 0.9.138):

binary	tests grouped	total
apalis_adapter	1	4
apalis_schema_contract	1	1
leave_migration_expand_contract	0	9

2 of 14 tests across those binaries were serialised, by a control that read as though it covered all of them. With binary(name): 4/4, 1/1, 9/9.

This is live regardless of whether the nextest runner is ever adopted — it's the mechanism ADR-0039 / DN-0005 P3 landed to keep cluster-global mutators off each other, and it has never worked.

The gate could not have caught it

check-nextest-config.mjs asserted each name appeared anywhere in the file, which the broken form satisfies. It validated spelling while the control was inert.

It now asserts the form that actually groups: binary(<name>) present, test(<name>) rejected with the remedy named. The filter block is extracted first so prose may quote the broken form while explaining it, and the extractor accepts all three TOML string shapes rather than only the multi-line one this repo happens to use — the pre-existing test used a single-quoted filter and caught that gap.

Mutation proof

input	result
committed config	0 failures
the exact pre-fix test() form	10 failures
one suite dropped from the filter	1 failure

Verification

check-nextest-config.mjs → OK · check-nextest-config.test.mjs → 7 pass, 0 fail · npm run check:ci-preflight → exit 0 · check-mjs-dark-suites --strict → exit 0 · show-config against the committed file → 4/4 and 9/9

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