Problem

Value.Default processes object schemas by iterating each property and resolving a default when the current value is undefined. The implementation called FromType twice for each property that needed a default:

1. Once to compute propertyValue (used only to check whether the result is an unassignable undefined)
2. Again to actually assign value[key]

// src/value/default/from_object.ts (before fix)
const propertyValue = FromType(context, type.properties[key], value[key])  // call 1
const isUnassignableUndefined = ...
if (isUnassignableUndefined) continue
value[key] = FromType(context, type.properties[key], value[key])           // call 2 — bug

For static defaults (default: 42) this double-call was harmless. For function-based defaults (default: () => …) the factory ran twice per absent property: the first return value was silently discarded and the second was assigned.

This is a real bug for any factory that produces unique values on each call — auto-increment IDs, timestamps, UUIDs, or any stateful generator:

let counter = 0
const T = Type.Object({
  id: Type.String({ default: () => `id-${++counter}` }),
})

Value.Default(T, {})
// Expected: { id: 'id-1' }, counter === 1
// Actual:   { id: 'id-2' }, counter === 2   ← factory called twice

Fix

Reuse the propertyValue already computed on the first call instead of invoking FromType a second time:

// src/value/default/from_object.ts (after fix)
const propertyValue = FromType(context, type.properties[key], value[key])
const isUnassignableUndefined = ...
if (isUnassignableUndefined) continue
value[key] = propertyValue   // ← reuse, no second call

Tests

Two new test cases added to test/typebox/runtime/value/default/object.ts:

• Should Default 33 — single factory property, verifies it is called exactly once and the correct value is assigned
• Should Default 34 — two factory properties, verifies each is called exactly once

Both tests fail before the fix and pass after. All 34,879 existing tests continue to pass.