fix: keep error data when formatErrors receives an error from a duplicate module copy - #18429

Bug

In a production build, REST error responses can lose data (for example a ValidationError's data.errors with the field paths). The status and message come through, but formatErrors returns { errors: [{ message }] }. This happens when the error was thrown by a different bundled copy of payload than the one running formatErrors, which #18420 traces to the route handler and page layers each getting their own copy.

Root cause

On 3.x, formatErrors only keeps data when incoming instanceof ValidationError || incoming instanceof APIError. Errors created by another copy of the module have different class identities, so both checks are false. The Mongoose fallback doesn't match either, since it compares name, which is minified. The error falls through to the message-only branch.

Solution

Backport the check that main already has: alongside instanceof, accept any error with isOperational === true (set in ExtendableError's constructor for every Payload error) that carries data. Behaviour for real instances is unchanged. This restores data. It does not touch the minified name (#13645), which is a separate problem.

Fixes #18420

Testing

• Added should keep data for a Payload error thrown by another copy of the error classes to packages/payload/src/utilities/formatErrors.spec.ts. It builds a ValidationError-shaped error from an unrelated class with a minified name. It fails on 3.x (no data in the result) and passes with this change.
• formatErrors.spec.ts: 8/8 passing.
• vitest run --project unit packages/payload/: 974/977 passing. The 3 failures are src/bin/index.spec.ts (CLI exit codes) and fail the same way without this change in my local setup.
• tsc --noEmit for packages/payload passes.