---
model: claude-opus-4-7[1m]
service: claude
timestamp: 2026-04-17T03:49:18Z
git_ref: 9703210
diff_cmd: git diff HEAD~1..HEAD
---

No code was produced in this turn — this is a design/planning
exchange for subint spawner support per issue #379. Captured
verbatim below are the two substantive AI responses, which
together fix the phased plan (A: modularize, B: subint, C:
harness) and the concrete Phase A file split before any
implementation begins.

## Turn 1 — initial triage + gating questions

> Read: issue #379, current `spawn/_spawn.py` (847 lines),
> and pyproject pins.
>
> ## Task summary
> Design/plan/implement subint backend per #379, plus
> modularize `spawn/_spawn.py` into per-backend submods, plus
> harness flag for test parametrization.
>
> ## Key finding
> `pyproject.toml:12` pins `requires-python = ">=3.12, <3.14"`
> — but `concurrent.interpreters` / PEP 734 **only lands in
> 3.14**. This is the load-bearing design question before
> coding.
>
> ## Proposed phasing (incremental commits)
> - **Phase A — modularize** `_spawn.py`: extract `trio_proc`
>   → `spawn/_trio.py`, `mp_proc` → `spawn/_mp.py`, keep
>   generic helpers (`hard_kill`/`soft_kill`/`new_proc`
>   dispatcher/`SpawnMethodKey`) in a slim core. Tests green
>   at each step.
> - **Phase B — `_subint` backend**: extend `SpawnMethodKey`
>   with `'subint'`; reuse UDS transport by default; shm is
>   escape-hatch follow-up.
> - **Phase C — harness**: add backend-parametrize flag, skip
>   subint when Python < 3.14.
>
> ## Gating questions before I start
> 1. **Python pin**: bump `<3.15` and feature-gate subint
>    tests (a), require 3.14 outright (b), or backport shim
>    (c)? I'd recommend (a).
> 2. **PR strategy**: one branch, commits per phase (current
>    `claude_bun_opus4.7_subint_spawner_backend`)? Or split
>    Phase A as its own PR first?
> 3. **`fork()`-via-subint hack** from the issue's "Our own
>    thoughts" section — v1 or follow-up? I'd defer to
>    follow-up.
> 4. **Prompt file line 32 is truncated** — what's the
>    existing harness flag name you had in mind ("using the
>    existing ___")?
>
> Which of these are already decided vs. open?

## User answers (for the raw record)

1. bump `<3.15`, feature-gate — option (a).
2. split Phase A as its own PR first.
3. defer `fork()`-via-subint hack.
4. harness flag is `--spawn-backend` CLI → `start_method`
   fixture, per `tractor._testing._pytest`. Prompt file
   updated accordingly.

## Turn 2 — concrete Phase A plan

> Good — prompt file now ends cleanly; harness flag
> confirmed as `--spawn-backend` CLI → `start_method`
> fixture (via `_testing/pytest.py:193,355`). Also noted
> `pytest.py:345-349` hardcodes valid backends as a string
> tuple — `typing.get_args(SpawnMethodKey)` should drive
> that list.
>
> ## Phase A — concrete plan (separate PR)
>
> **File split** in `tractor/spawn/`:
> - `_spawn.py` stays as "core": keeps `SpawnMethodKey`,
>   `_spawn_method`, `proc_waiter`, `try_set_start_method`,
>   `exhaust_portal`, `cancel_on_completion`, `hard_kill`,
>   `soft_kill`, `new_proc` dispatcher, `_methods`
>   registry. Kept at this path so `_testing/pytest.py:228`
>   and other external imports don't break.
> - `_trio.py` ← `trio_proc()` (lines 448–671, ~224 lines)
> - `_mp.py` ← `mp_proc()` (lines 672–842, ~171 lines)
> - `_methods` dict imports the two backend fns from the
>   new modules.
>
> **Commits** (each green via `/run-tests`):
> 1. Drive `_testing/pytest.py` backend-tuple from
>    `get_args(SpawnMethodKey)` — tiny prep.
> 2. Extract `trio_proc` → `spawn/_trio.py`; `_methods`
>    imports it.
> 3. Extract `mp_proc` → `spawn/_mp.py`; `_methods`
>    imports it.
> 4. Tidy `spawn/__init__.py` docstring to describe new
>    layout.
>
> No pyproject pin bump in Phase A (that's Phase B).
>
> **Workflow**: I'd run this in a new worktree via
> `/open-wkt spawn_modularize` (branch
> `wkt/spawn_modularize`), then open a PR before returning
> to the current `claude_bun_opus4.7_subint_spawner_backend`
> branch for Phase B/C.
>
> Green-light to `/open-wkt` and start Phase A?

## User final response

> all this first then yes, green light.

— log this `/prompt-io` entry first, then proceed with
Phase A in a worktree.
