RFM row: an unsolved inference placeholder reads back as the type Unit (fabricated type in a refusal)

[gunbai-bot]

Files one row under dag/gunbc/recurring_failure_mode/: unsolved_placeholder_reads_back_as_unit. No code changes. Filed on the program owner's ruling.

Specimen. Executed 2026-10-05 with gunbc run, using gunbc built at main ed68b5573b. This code refuses with no field 'module' on type 'Unit':

let modules = fold_list(xs: ms(), empty: [], cons: fn(acc, m) { acc })
match modules |> first { Present { value: m } => m.module ... }

The element's type is the unsolved empty_list_element placeholder, and it was never Unit. The same read over list_snoc_item(xs: [], ..) refuses with the true cause: the scrutinee's type is unresolved, give it a declared type.

Harm. No wrong program is accepted, but the refusal names a type the program never had. That cost two falsified repair rounds on #13330.

Producer: not located. The row says so, lists the unread candidates, and names the run that would decide it. It does not assert a cause.

Standing. Rung: mitigatable. Ceiling: 3. Next trigger: an unsolved placeholder at field access refuses with the unresolved-type cause.

Resolve check: --function __no_such_function__ on the file returns NoSuchFunction.

🤖 Generated with Claude Code

[briansrls]

LAND. This is a distinct residual from the earlier empty-list fabrication repair: the empty literal now carries the honest empty_list_element TypeVariable, but one downstream path later reports that still-unsolved placeholder as concrete Unit at field access. The row does not guess which candidate performs that substitution; it records the contrasting list_snoc_item refusal, names the unread candidates, and states the experiment that would locate the producer.

The standing is honest. The program is refused rather than accepted, so this is a loud but materially misattributed diagnostic; mitigatable is appropriate. A modeled TypeVariable can be refused as unresolved without inventing a concrete type, so the stated ceiling and trigger are reachable. The accepted control is also the right boundary: the same fold with a declared element/return type must continue to work. Exact-head witnesses are green.