- Replace z.strict() with z.strictObject() and z.passthrough() with z.looseObject()
- Update z.function() calls to object syntax: {input: [...], output: ...}
- Change ZodError.errors to .issues everywhere
- Update z.record() calls to include both key and value schemas
- Remove errorMap parameter from parseAsync() calls (no longer supported)
- Fix ZodErrorMap callback signature with as any cast
- Add @ts-expect-error for Zod 4 RefinementCtx.path type issue
- Cast z.looseObject() results with as any where type inference fails
- 53 errors reduced to 3 remaining (type definition issues, not Zod API)

- Update z.record() to use 2-arg form (key, value schema)
- Update z.function() to use { input: [], output: schema } syntax
- Replace .error.errors with .error.issues in Zod 4
- Remove errorMap option parameters (not supported in Zod 4)
- Add type assertions for complex generic constraints
- Fix .default() to support function form in integration config

- Fix formDataToObject to check `_def.catchall` instead of `unknownKeys` for passthrough detection in Zod 4
- Fix handleFormDataGetAll to use `_def.element` instead of `_def.type` for accessing array element validators in Zod 4
- Update config-validate tests to use `.issues` instead of `.errors` for ZodError in Zod 4

- Changed errorMap from Zod 3's (baseError, ctx) to Zod 4's (iss) signature
- Updated z.config() to use customError callback instead of z.setErrorMap()
- Use iss.input instead of received for invalid_type/invalid_literal errors
- Show received type name instead of actual value for type mismatch errors
- Add handling for too_small errors in validation
- Add error handling in customError callback to fallback gracefully