First doc of a new `ai/tpt-backends/` set: the normative
description of what a `tractor` tpt backend *is* as of `main`,
written so the 3 sibling plans (TIPC, QUIC, `wg`) can be worked
independently (by another model/provider) w/o design drift.
Deats,
- the backend duck-type as empirically derived from
`_tcp.py`/`_uds.py`: the `Address` protocol surface, the
mod-level `start_listener()`/`close_listener()` pair and
`Msgpack<Proto>Stream(MsgpackTransport)`.
- the ONE reflection you can't break:
`Endpoint.start_listener()` resolves the tpt mod via
`inspect.getmodule(self.addr)`, so an `Address` type and its
listener fns MUST live in the same mod.
- a 10-item registration checklist (`_address_types`,
`_key_to_transport`, `_addr_to_transport`, `wrap_address()`
match-cases, `TransportProtocolKey`, maddr tables, ..) incl.
the import-time `_default_lo_addrs` trap.
- where the `trio.SocketListener` assumption is *actually*
load-bearing (just the `getsockname()` reconcile) vs. merely
annotated.
- the handshake/discovery invariants a new backend inherits,
dep policy (extras + import-laziness per the #470 boot-latency
budget), `--tpt-proto` harness plumbing and code style.
Also, records a verified finding the plans lean on hard:
`trio.SocketStream`/`SocketListener` are addr-*family* agnostic
— the only ctor checks are "is a trio sock" + `SOCK_STREAM` (+
an `OSError`-suppressed `SO_ACCEPTCONN`) — so any `SOCK_STREAM`
family CPython can make drops into the existing
`trio.serve_listeners()` path unmodified.
(this patch was generated in some part by `claude-code` using `claude-opus-5` (`anthropic`))
Gud Boi