Summary

• Fixes v5 - Incompatible with arktype even though it uses standard schema #5110: arktype schemas are callable (typeof === 'function'), so isStandardSchema() was rejecting them because isObject() only accepts typeof === 'object'
• Updated isStandardSchema to accept both objects and functions with the ~standard property, matching the standard schema spec
• Added comprehensive tests for isStandardSchema covering callable schemas, primitives, arrays, and plain objects

Details

The root cause was in packages/vee-validate/src/utils/assertions.ts:

// Before (broken for arktype)
export function isStandardSchema(value: unknown): value is StandardSchemaV1 {
  return isObject(value) && '~standard' in (value as unknown as StandardSchemaV1);
}

// After (works with arktype and any callable standard schema)
export function isStandardSchema(value: unknown): value is StandardSchemaV1 {
  return !!value && (typeof value === 'object' || typeof value === 'function') && '~standard' in (value as Record<PropertyKey, unknown>);
}

Arktype schemas are both functions and standard schemas — they are callable but also have the ~standard property. The isObject() utility uses typeof obj === 'object' which returns false for functions, causing isStandardSchema() to return false for arktype schemas. This made vee-validate fall through to the isCallable(rules) branch, which tried to call the arktype schema as a plain validation function, leading to TypeError: rule is not a function.

Test plan

• Added 6 new tests for isStandardSchema in assertions.spec.ts
• Tests cover: plain object standard schemas, callable standard schemas (arktype-like), plain functions, primitive values, arrays, and plain objects without ~standard
• All 361 existing tests continue to pass (3 pre-existing failures unrelated to this change)

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