chore(changeset): auth ValidationError 4xx mapping (#3398)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: baozhoutao

.changeset/auth-validationerror-4xx-mapping.md

@@ -0,0 +1,18 @@
+---
+"@objectstack/plugin-auth": patch
+---
+
+fix(auth): map ObjectQL `ValidationError` to a 4xx on the better-auth paths (#3398)
+
+A field-level validation failure raised by the ObjectQL record-validator
+(e.g. an invalid `image` on `POST /api/v1/auth/update-user`) surfaced to the
+HTTP client as a **raw 500 with an empty body**. better-auth only maps its own
+`APIError`s to structured responses; any other error thrown from an adapter
+method propagates to better-call's router as an unhandled fault → `500 {}`.
+
+Added the auth-path analogue of the REST layer's `mapDataError`: the objectql
+adapter now detects the ObjectQL validation envelope at its boundary (duck-typed
+by `code` / `name`, so plugin-auth keeps no hard dependency on
+`@objectstack/objectql` and cross-realm `instanceof` can't bite) and re-throws
+it as `APIError('BAD_REQUEST', …)`. `update-user` and friends now answer with a
+`400 { code: 'VALIDATION_FAILED', message, fields }` instead of an opaque 500.