When Nest resolves a @Body() metatype to Object (import-type erasure #436,
or decorator-metadata loss in a broken dependency graph — the #1391/#1389
mixed-install class), the global ValidationPipe's whitelist rejects every
property of every payload: the first symptom is a 400 on the first
bootstrap attempt of a fresh install, indistinguishable from a bad payload.
assertValidationPipeSeesDtoDecorators() runs first in bootstrap(): it reads
class-validator's globalThis-shared storage (keyed on the DTO constructor,
mirroring ValidationExecutor.js:50's object.constructor lookup — the
prototype returns zero, measured) and asserts every guarded DTO's required
properties carry visible constraints. Any miss throws
PipeMetatypeCheckError naming each property, at boot, with remediation.
Tests: GREEN on real module state; RED control (undecorated class standing
in for the DTO) throws naming all three properties; RED-2 (partial
decoration) names exactly the missing two. Typecheck delta vs pristine
tree: zero errors from these files.
Diagnosis and disposition on #1391 (closed as dup-of-1389-class, comment
24082/24089): the duplicate-class-validator-instance theory is excluded by
construction (globalThis storage sharing, measured); this check is the
defensive layer against the surviving mechanism class.
code-infra-01