ADR 0038: The corpus keeps its untyped boundary, and it costs six rules rather than sixteen

Status: Accepted 2026-08-26 · answers the question 0036 deferred; depends on 0037 for its numbers

Context

ADR 0036 left an open question: sixteen type-aware rules were off across test/**, scripts/** and tools/**, and the reason given for all of them was test/corpus/untyped.ts, the module that declares type Untyped = any on purpose. If a declared any costs sixteen rules over the whole harness, the declaration is worth re-examining. So the question was put as "should the corpus adapter still have an any boundary?" and parked.

It was the wrong question, because the premise was wrong. Ten of those sixteen rules were not reporting the boundary at all. They were reporting the tsconfig mismatch ADR 0037 describes, and they went to zero the moment the linter could see the same compiler options tsc uses. The exemption list was measured honestly and measured the wrong thing.

What the boundary actually is

CorpusApi is not any and has not been for some time. It is derived from the adapter object, so a case sees the name, the arguments and the return type of every capability it calls. Untyped is what is left: 288 occurrences, and its module comment sorts them into the two kinds that remain.

• Case specs. The declarative {sheets: [{cells: [...]}]} a case hands buildFrom, and the options bags built around it. Writing that type down is a real piece of design work, not an annotation: the spec language is the corpus's own DSL.
• Report accumulators. Record<string, Untyped>, the shape a capability builds its findings into. Widening it to unknown types nothing; it moves the debt into the 254 cases that read the report.

Everything else has been paid off, and untyped.ts says so at the site, with the grep that counts the balance.

Decision

The boundary stands. The exemption it earns is narrowed to what it actually reaches: test/corpus/** only, and six rules rather than sixteen.

rule	findings	why it is off
no-unsafe-member-access	803	a case reads its report through Record<string, Untyped>
await-thenable	699	cases await every capability so one can turn async without touching 282 call sites
no-unsafe-assignment	373	destructuring that report
no-unsafe-argument	122	handing a spec back into a capability
no-unsafe-call	66	calling through the untyped surface on purpose
no-unsafe-return	48	an adapter capability returning its accumulator

2111 findings, and the sample checked by hand traces where the table says: a case's (await api.roundtripWorkbook(SPEC)).sheets.S.cells.A1 is three of them at once. None is a defect; each is the design being reported.

Ten rules came back on: no-unnecessary-type-assertion, no-base-to-string, no-misused-spread, require-array-sort-compare, restrict-template-expressions, only-throw-error, prefer-promise-reject-errors, restrict-plus-operands, unbound-method and no-unsafe-enum-comparison. All ten now report zero everywhere, the corpus included. Sixty-six findings were fixed to get there, 35 inside test/corpus/** and 31 in src/**/*.test.ts, scripts/ and tools/. Two were worth the trip on their own: [...s] iterating code points where a CFB stream name is UTF-16 code units, and String(v) on a CellValue rendering every non-primitive shape as [object Object] in a probe's own failure output.

Why not type it

An adapter returning fully typed values would let those six rules run over the harness, which is where a regression in the corpus itself would show up. That is a real gain and it is not free: it is a rewrite of test/corpus/adapters/ts-xlsx/** and of the report shapes all 282 cases are written against, and the case-spec DSL would have to be designed rather than inferred.

At sixteen rules across three trees that trade looked worth arguing about. At six rules over test/corpus/**, a directory whose entire job is to describe behaviour from outside the library, it does not. The corpus's value is that a case cannot see how the library is built; the boundary is a weaker version of the same idea, and the rules it silences are the ones that exist to complain about exactly that.

Revisit when

• The case-spec DSL is written down as a type for some other reason. Then the largest of the two remaining classes is already paid for and the balance changes.
• The count in untyped.ts starts climbing. It is 288 today, and the module comment carries the command that measures it. A boundary that is being spent rather than held is a different decision from this one.