fix(interpreter): process redirections transactionally (#349)

* fix(interpreter): process redirections transactionally

* test(interpreter): align redirection transaction coverage

* fix(interpreter): preserve descriptor transaction state

* fix(interpreter): use live descriptor path

* fix(interpreter): preserve standard descriptor routes

* fix(interpreter): reject closed descriptor duplication

* fix(interpreter): share redirected descriptor positions

* fix(interpreter): retain fd input for non-readers

* fix(interpreter): track descriptor stdin consumption

* fix(interpreter): detect descriptor stdin reads

* refactor(interpreter): simplify redirection policies

* refactor(interpreter): remove duplicate redirection policy