Check for Engin-injected parameter using the dependency function name

CHANGELOG.md

@@ -5,6 +5,15 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.3.1] - 2025-11-30
+
+### Fixed
+
+- Fixed compatibility with `fastapi>=0.121.3`
+  - FastAPI `Depends` [was changed to a frozen dataclass in `v0.121.3`](https://fastapi.tiangolo.com/release-notes/#01213). 
+  - Engin no longer attaches a magic `__engin__` attribute to `Depends` for dependency detection in the `engin graph` tool.
+  - FastAPI dependencies created via `engin.Inject()` are now identified by a dedicated function name (`__inner_engin_dependency__`).
+
 ## [0.3.0] - 2025-11-12
 
 ### Added

src/engin/extensions/fastapi.py

@@ -53,16 +53,14 @@ def graph(self) -> list[Node]:
 
 
 def Inject(interface: type[T]) -> Depends:
-    async def inner(conn: HTTPConnection) -> T:
+    async def __inner_engin_dependency__(conn: HTTPConnection) -> T:
         try:
             assembler: Assembler = conn.app.state.assembler
         except AttributeError:
             raise RuntimeError("Assembler is not attached to Application state") from None
         return await assembler.build(interface)
 
-    dep = Depends(inner)
-    dep.__engin__ = True  # type: ignore[attr-defined]
-    return dep
+    return Depends(__inner_engin_dependency__)
 
 
 class _FastAPIDependencyGrapher(DependencyGrapher):
@@ -181,7 +179,12 @@ def _is_injected_param(param: Parameter) -> bool:
         args = typing.get_args(param.annotation)
         if len(args) != 2:
             return False
-        return isinstance(args[1], Depends) and hasattr(args[1], "__engin__")
+        return (
+            isinstance(args[1], Depends)
+            and (depenency_function := getattr(args[1], "dependency", None)) is not None
+            and inspect.isfunction(depenency_function)
+            and depenency_function.__name__ == "__inner_engin_dependency__"
+        )
 
     @property
     def name(self) -> str: