Compare the complete canonical `Nursery.start()` protocol error
before re-surfacing ambient cancellation. Preserve child-owned
`RuntimeError` objects whose messages only resemble Trio's wording.
Cover the colliding prefix and assert the original error remains the
exception group's sole leaf.
Review: PR #479 (goodboy)
https://github.com/goodboy/tractor/pull/479
(this patch was generated in some part by `opencode` using
`gpt-5.6-sol` (`openai`))
Gud Boi
1c7d0c7f3e