Raise `ValueError` from `open_root_actor()` when any
`registry_addrs` entry uses a transport proto not in
`enable_transports` — historically this caused a
silent indefinite hang during the registrar handshake
(the actor could never connect to register/discover).
Also,
- update `test_root_passes_tpt_to_sub` to detect a
proto mismatch between parametrized `tpt_proto_key`
and CLI `tpt_proto`, asserting the new guard raises
`ValueError` with expected msg content.
- replace old commented-out notes with a clearer
explanation of the mismatch foot-gun.
(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
(cherry picked from commit d036ef7d7f)
Gud Boi
a0456fece4