fix: resolve ForwardRef inside Annotated in get_typed_annotation

When a type annotation uses a string literal inside Annotated, e.g.
Annotated['Potato', Depends(get_potato)], Python stores it as
Annotated[ForwardRef('Potato'), Depends(get_potato)] at runtime.

get_typed_annotation only handled the case where the annotation itself
is a string/ForwardRef. It did not recurse into Annotated's first
argument. As a result, the ForwardRef was never resolved, FastAPI
could not identify the type, and the parameter was treated as Any,
producing an incorrect OpenAPI schema.

Fix by also handling the case where annotation is ForwardRef directly
(not wrapped in a string), and by recursively resolving any
ForwardRef found as the first argument of an Annotated type.

Fixes #13056

fastapi/dependencies/utils.py

@@ -245,9 +245,22 @@ def get_typed_signature(call: Callable[..., Any]) -> inspect.Signature:
 def get_typed_annotation(annotation: Any, globalns: dict[str, Any]) -> Any:
     if isinstance(annotation, str):
         annotation = ForwardRef(annotation)
-        annotation = evaluate_forwardref(annotation, globalns, globalns)
+    if isinstance(annotation, ForwardRef):
+        annotation = evaluate_forwardref(annotation, globalns, globalns)  # ty: ignore[deprecated]
         if annotation is type(None):
             return None
+    # Resolve any ForwardRef inside the first argument of Annotated.
+    # Python automatically wraps string args in ForwardRef, e.g.:
+    #   Annotated["Potato", Depends(get_potato)]
+    # becomes Annotated[ForwardRef("Potato"), Depends(get_potato)] at runtime.
+    # Without this, FastAPI never sees the resolved type and treats the
+    # parameter as Any, producing an incorrect OpenAPI schema.
+    if get_origin(annotation) is Annotated:
+        args = get_args(annotation)
+        first_arg = args[0]
+        if isinstance(first_arg, (str, ForwardRef)):
+            resolved_first = get_typed_annotation(first_arg, globalns)
+            annotation = Annotated[tuple([resolved_first] + list(args[1:]))]
     return annotation