`run()` described its actor-selection kwargs as placement controls,
but they determine who owns the actor lifetime and whether an existing
actor is reused or a new one is spawned.
Use lifetime-management terminology in the parameter comments and
docstring, and identify the existing-actor handle as `portal: Portal`.
Review: PR #481 (goodboy)
https://github.com/goodboy/tractor/pull/481#pullrequestreview-5012942328
(this patch was generated in some part by `opencode` using `gpt-5.6-sol` (`openai`))