[LinusOssmann]

Problem

wrapSupabaseFn is used for custom list, create, update and delete functions, but it always treats the first argument as params: const { onError } = params. syncedCrud calls the write functions as fn(input, params), so for writes onError is read from the row and is undefined. When a custom write returns { error }, the wrapper throws TypeError: onError is not a function. The user's onError receives that TypeError with source: 'set' instead of the server error with source: 'create'/'update', and there is no revert. Server rejections of custom writes (RLS, constraints, …) are effectively invisible.

Fix

Keep the existing behavior for list. For writes, take onError from the second argument and route the error through handleSupabaseError with the same params the built-in create/update/delete pass (type: 'set', input, revert).

Test

tests/supabase-custom-fns.test.ts: a custom create and a custom update that return an RLS error. On main onError receives "onError is not a function"; with the fix it receives the server message, the right source and a revert function.