Bug(OpenAPI): Schema generation doesn't resolve signature types for "nested" objects

[floxay]

Description

OpenAPI schema generation fails if it encounters a "nested" object with a type which is not available at runtime but could be resolved using signature types/namespaces.

URL to code causing the issue

No response

MCVE

main.py

from litestar import Litestar, get

from external_module import Item
from schemas import ItemContainer

@get(sync_to_thread=False, signature_namespace={"Item": Item})
def handler() -> ItemContainer:
    return ItemContainer(items=[])

app = Litestar(
    route_handlers=[handler],
    signature_types=(Item,),
    debug=True,
)

schemas.py

from __future__ import annotations

from dataclasses import dataclass

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from external_module import Item

@dataclass
class ItemContainer:
    items: list[Item]

external_module.py

from dataclasses import dataclass

@dataclass
class Item:
    foo: str = "bar"

Steps to reproduce

1. Run the above code
2. See error at `http://127.0.0.1:8000/schema` (`name 'Item' is not defined`)
3. `http://127.0.0.1:8000` still works.

Screenshots

No response

Logs

No response

Litestar Version

2.10.0

Platform

• Linux
• Mac
• Windows
• Other (Please specify in the description above)

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