- Defaults for omitted Query, Header, Cookie, Form parameters and model fields are no longer treated as user input; validation runs only when `validate_default=True` is set.
- Default factories now execute once, omitted defaults are excluded from model dumps (unless explicitly set), and validation errors no longer include injected defaults.
- This change is breaking for code that relied on automatic validation of omitted values; enable it via `Field(validate_default=True)` or `Query(validate_default=True)`.