@Inject() arity not checked (DECORATOR_ARITY_WRONG) #550

@Inject() arity is not checked in the DI paths (extract_param_dependency and siblings).

Upstream getConstructorDependencies (di.ts) reports DECORATOR_ARITY_WRONG unless @Inject is called with exactly one argument. Here @Inject() (zero args) silently falls back to the type annotation and @Inject(A, B) takes the first arg.

Only diverges on malformed decorators. Same gap likely exists wherever param decorators are parsed (injectable / directive / pipe / ng_module paths).

Found in PR #548 review.