Drop subint-family gate from `main_thread_forkserver`

`main_thread_forkserver` doesn't actually need py3.14
`concurrent.interpreters` (PEP 734) — it forks from a
non-trio worker thread and runs `_trio_main` in the child,
same shape as `trio_proc`. The previous `_has_subints`
gate + subint-family `case` arm were a copy-paste error.

In `tractor.spawn._main_thread_forkserver`,
- drop the `_has_subints` import + the `RuntimeError`
  raise in `main_thread_forkserver_proc()`.
- drop the now-unused `import sys` (only used by the
  prior error msg).

In `tractor.spawn._spawn.try_set_start_method()`,
- pull `'main_thread_forkserver'` out of the subint-
  family arm (which still gates on `_has_subints`).
- merge it into the `'trio'` arm — both set `_ctx = None`
  bc neither needs an `mp.context`.

(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

.github/workflows/ci.yml

@@ -148,9 +148,13 @@ jobs:
       - name: Run tests
         run: >
           uv run
-          pytest tests/ -rsx
+          pytest
+          tests/
+          -rsx
           --spawn-backend=${{ matrix.spawn_backend }}
           --tpt-proto=${{ matrix.tpt_proto }}
+          --capture=fd
+        # ^XXX^ can't work with --spawn-method=main_thread_forkserver
 
   # XXX legacy NOTE XXX
   #

pyproject.toml

@@ -62,6 +62,7 @@ dev = [
   {include-group = 'devx'},
   {include-group = 'testing'},
   {include-group = 'repl'},
+  {include-group = 'sync_pause'},
 ]
 devx = [
   # `tractor.devx` tooling

tests/devx/conftest.py

@@ -4,6 +4,7 @@
 '''
 from __future__ import annotations
 import platform
+import os
 import signal
 import time
 from typing import (
@@ -56,6 +57,7 @@ type PexpectSpawner = Callable[
 @pytest.fixture
 def spawn(
     start_method: str,
+    loglevel: str,
     testdir: pytest.Pytester,
     reg_addr: tuple[str, int],
 
@@ -67,11 +69,12 @@ def spawn(
     '''
     supported_spawners: set[str] = {
         'trio',
-        # ?TODO, other spawners that will work?
+        # `examples/debugging/<script>.py` picks up the spawn
-        # - [ ] need to pass `start_method={spawner}` to underlying
+        # backend via the `TRACTOR_SPAWN_METHOD` env-var which
-        #      `examples/debugging/<script>.py` somehow?
+        # is honored inside `tractor._root.open_root_actor()`,
-        # 'main_thread_forkserver',
+        # so no per-script edits are required.
-        # 'subint_forkserver',
+        'main_thread_forkserver',
+        'subint_forkserver',
     }
     if start_method not in supported_spawners:
         pytest.skip(
@@ -88,12 +91,35 @@ def spawn(
         https://docs.python.org/3/using/cmdline.html#using-on-controlling-color
 
         '''
-        import os
         # disable colored tbs
         os.environ['PYTHON_COLORS'] = '0'
         # disable all ANSI color output
         # os.environ['NO_COLOR'] = '1'
 
+    def set_spawn_method():
+        '''
+        Drive the actor-spawn backend inside the spawned
+        `examples/debugging/<script>.py` subproc via env-var
+        (consumed by `tractor._root.open_root_actor()`),
+        without requiring per-script CLI plumbing.
+
+        '''
+        os.environ['TRACTOR_SPAWN_METHOD'] = start_method
+
+    def set_loglevel():
+        '''
+        Forward the test-suite parametrized `loglevel` into the
+        spawned `examples/debugging/<script>.py` subproc via
+        env-var (consumed by `tractor._root.open_root_actor()`),
+        so console verbosity can be cranked or silenced from
+        the test harness without per-script edits.
+
+        '''
+        if loglevel:
+            os.environ['TRACTOR_LOGLEVEL'] = loglevel
+        else:
+            os.environ.pop('TRACTOR_LOGLEVEL', None)
+
     spawned: PexpectSpawner|None = None
 
     def _spawn(
@@ -103,6 +129,8 @@ def spawn(
     ) -> pty_spawn.spawn:
         nonlocal spawned
         unset_colors()
+        set_spawn_method()
+        set_loglevel()
         spawned = testdir.spawn(
             cmd=mk_cmd(
                 cmd,
@@ -146,6 +174,14 @@ def spawn(
         if ptyproc.isalive():
             ptyproc.kill(signal.SIGKILL)
 
+    # Scope our env-var mutations to this single fixture invocation
+    # — both `TRACTOR_SPAWN_METHOD` and `TRACTOR_LOGLEVEL` are
+    # honored by `tractor._root.open_root_actor()` so leaking them
+    # past this test could inadvertently re-route a later in-process
+    # tractor test's spawn-backend / loglevel.
+    os.environ.pop('TRACTOR_SPAWN_METHOD', None)
+    os.environ.pop('TRACTOR_LOGLEVEL', None)
+
     # TODO? ensure we've cleaned up any UDS-paths?
     # breakpoint()
 

tests/devx/test_debugger.py

@@ -841,7 +841,7 @@ def test_multi_nested_subactors_error_through_nurseries(
     )
 
 
-@pytest.mark.timeout(15)
+# @pytest.mark.timeout(15)
 @has_nested_actors
 def test_root_nursery_cancels_before_child_releases_tty_lock(
     spawn,

tests/discovery/test_registrar.py

@@ -535,13 +535,13 @@ async def kill_transport(
 # At timeout the plugin hard-kills the pytest process — that's
 # the intended behavior here; the alternative is an unattended
 # suite run that never returns.
-@pytest.mark.timeout(
+# @pytest.mark.timeout(
-    30,
+#     30,
-    # NOTE should be a 2.1s happy path.
+#     # NOTE should be a 2.1s happy path.
-    # XXX for `main_thread_forkserver` this is SUPER SENSITIVE
+#     # XXX for `main_thread_forkserver` this is SUPER SENSITIVE
-    # so keep it higher to avoid flaky runs..
+#     # so keep it higher to avoid flaky runs..
-    method='thread',
+#     method='thread',
-)
+# )
 @pytest.mark.skipon_spawn_backend(
     'subint',
     # 'main_thread_forkserver',

tests/spawn/test_main_thread_forkserver.py

@@ -182,7 +182,7 @@ async def run_fork_in_non_trio_thread(
 # `subint_sigint_starvation_issue.md`. Each test also has an
 # inner `trio.fail_after()` so assertion failures fire fast
 # under normal conditions.
-@pytest.mark.timeout(30, method='thread')
+# @pytest.mark.timeout(30, method='thread')
 def test_fork_from_worker_thread_via_trio(
 ) -> None:
     '''

tests/spawn/test_subint_cancellation.py

@@ -179,10 +179,10 @@ def test_subint_happy_teardown(
 # `subint_sigint_starvation_issue.md` GIL-starvation flavor,
 # so `method='thread'` keeps us safe in case ordering or
 # load shifts the failure mode.
-@pytest.mark.timeout(
+# @pytest.mark.timeout(
-    3,  # NOTE never passes pre-3.14+ subints support.
+#     3,  # NOTE never passes pre-3.14+ subints support.
-    method='thread',
+#     method='thread',
-)
+# )
 def test_subint_non_checkpointing_child(
     reg_addr: tuple[str, int|str],
 ) -> None:

tests/test_advanced_streaming.py

@@ -430,10 +430,10 @@ async def inf_streamer(
     print('streamer exited .open_streamer() block')
 
 
-@pytest.mark.timeout(
+# @pytest.mark.timeout(
-    6,
+#     6,
-    method='signal',
+#     method='signal',
-)
+# )
 def test_local_task_fanout_from_stream(
     reg_addr: tuple,
     debug_mode: bool,

tests/test_cancellation.py

@@ -458,10 +458,10 @@ async def spawn_and_error(
 # `test_nested_multierrors`. See
 # `ai/conc-anal/subint_forkserver_test_cancellation_leak_issue.md`
 # / #449 for the post-mortem.
-@pytest.mark.timeout(
+# @pytest.mark.timeout(
-    10,
+#     10,
-    method='thread',
+#     method='thread',
-)
+# )
 @tractor_test
 async def test_nested_multierrors(
     reg_addr: tuple,

tractor/_root.py

@@ -241,6 +241,7 @@ async def open_root_actor(
             f'_registry_addrs: {registry_addrs!r}\n'
         )
 
+    # debug.mk_pdb().set_trace()
     async with maybe_block_bp(
         debug_mode=debug_mode,
         maybe_enable_greenback=maybe_enable_greenback,
@@ -284,6 +285,75 @@ async def open_root_actor(
             )
             enable_modules.extend(rpc_module_paths)
 
+        # `TRACTOR_LOGLEVEL` env-var wins over any caller-passed
+        # `loglevel` so devs/test-runs can crank (or silence)
+        # console verbosity without touching application code.
+        env_ll_report: str = ''
+        if env_ll := os.environ.get('TRACTOR_LOGLEVEL'):
+            loglevel = env_ll
+            env_ll_report: str = (
+                f'Detected env-var setting,\n'
+                f'TRACTOR_LOGLEVEL={env_ll!r}\n'
+                f'\n'
+                f'Setting console loglevel per,\n'
+                f'loglevel={loglevel!r}\n'
+            )
+            if (
+                loglevel
+                and
+                loglevel.upper() != env_ll.upper()
+            ):
+                env_ll_report += (
+                    f'\n'
+                    f'NOTE env-var OVERRIDES caller-passed,\n'
+                    f'loglevel={loglevel!r}\n'
+                )
+
+        loglevel: str = (
+            loglevel
+            or
+            log._default_loglevel
+        )
+        loglevel: str = loglevel.upper()
+
+        assert loglevel
+        _log = log.get_console_log(
+            level=loglevel,
+            name='tractor',
+            logger=logger,
+        )
+        assert _log
+        if env_ll_report:
+            _log.info(env_ll_report)
+
+        # `TRACTOR_SPAWN_METHOD` env-var wins over any caller-passed
+        # `start_method` so devs/test-runs can swap the actor spawn
+        # backend without touching application code (e.g. driving
+        # the `examples/debugging/<script>.py` suite under each
+        # backend from `tests/devx/conftest.py::spawn`).
+        if env_sm := os.environ.get('TRACTOR_SPAWN_METHOD'):
+            start_method: str = env_sm
+            env_sm_report: str = (
+                f'Detected env-var setting,\n'
+                f'TRACTOR_SPAWN_METHOD={env_sm!r}\n'
+                f'\n'
+                f'Setting spawn backend as,\n'
+                f'start_method={env_sm!r}\n'
+            )
+            if (
+                start_method
+                and
+                start_method != env_sm
+            ):
+                _log.warning(
+                    env_sm_report
+                    +
+                    f'NOTE env-var OVERRIDES caller-passed,\n'
+                    f'`start_method={start_method!r}`\n'
+                )
+            else:
+                _log.info(env_sm_report)
+
         if start_method is not None:
             _spawn.try_set_start_method(start_method)
 
@@ -300,12 +370,6 @@ async def open_root_actor(
             wrap_address(uw_addr)
             for uw_addr in uw_reg_addrs
         ]
-        loglevel: str = (
-            loglevel
-            or
-            log._default_loglevel
-        )
-        loglevel: str = loglevel.upper()
 
         # Debug-mode is currently only supported for backends whose
         # subactor root runtime is trio-native (so `tractor.devx.
@@ -341,13 +405,6 @@ async def open_root_actor(
                 f'{_spawn._spawn_method!r}.'
             )
 
-        assert loglevel
-        _log = log.get_console_log(
-            level=loglevel,
-            name='tractor',
-        )
-        assert _log
-
         # TODO: factor this into `.devx._stackscope`!!
         if (
             debug_mode

tractor/spawn/_main_thread_forkserver.py

@@ -346,7 +346,6 @@ from __future__ import annotations
 import errno
 import os
 import signal
-import sys
 import threading
 from functools import partial
 from typing import (
@@ -370,7 +369,6 @@ from ._spawn import (
     cancel_on_completion,
     soft_kill,
 )
-from ._subint import _has_subints
 
 if TYPE_CHECKING:
     from tractor.discovery._addr import UnwrappedAddress
@@ -832,13 +830,6 @@ async def main_thread_forkserver_proc(
     thread instead of `trio.lowlevel.open_process()`.
 
     '''
-    if not _has_subints:
-        raise RuntimeError(
-            f'The {"main_thread_forkserver"!r} spawn backend '
-            f'requires Python 3.14+.\n'
-            f'Current runtime: {sys.version}'
-        )
-
     # Backend-scoped config pulled from `proc_kwargs`. Using
     # `proc_kwargs` (vs a first-class kwarg on this function)
     # matches how other backends expose per-spawn tuning

tractor/spawn/_spawn.py

@@ -135,13 +135,15 @@ def try_set_start_method(
         case 'mp_spawn':
             _ctx = mp.get_context('spawn')
 
-        case 'trio':
+        case (
+            'trio'
+            | 'main_thread_forkserver'
+        ):
             _ctx = None
 
         case (
             'subint'
             | 'subint_fork'
-            | 'main_thread_forkserver'
             | 'subint_forkserver'
         ):
             # All subint-family backends need no `mp.context`;

uv.lock

@@ -682,6 +682,7 @@ dependencies = [
 
 [package.dev-dependencies]
 dev = [
+    { name = "greenback", marker = "python_full_version < '3.14'" },
     { name = "pexpect" },
     { name = "prompt-toolkit" },
     { name = "psutil" },
@@ -736,6 +737,7 @@ requires-dist = [
 
 [package.metadata.requires-dev]
 dev = [
+    { name = "greenback", marker = "python_full_version == '3.13.*'", specifier = ">=1.2.1,<2" },
     { name = "pexpect", specifier = ">=4.9.0,<5" },
     { name = "prompt-toolkit", specifier = ">=3.0.50" },
     { name = "psutil", specifier = ">=7.0.0" },
@@ -744,7 +746,7 @@ dev = [
     { name = "pytest-timeout", specifier = ">=2.3" },
     { name = "stackscope", specifier = ">=0.2.2,<0.3" },
     { name = "typing-extensions", specifier = ">=4.14.1" },
-    { name = "xonsh", editable = "../xonsh" },
+    { name = "xonsh", specifier = ">=0.23.0" },
 ]
 devx = [
     { name = "stackscope", specifier = ">=0.2.2,<0.3" },
@@ -756,7 +758,7 @@ repl = [
     { name = "prompt-toolkit", specifier = ">=3.0.50" },
     { name = "psutil", specifier = ">=7.0.0" },
     { name = "pyperclip", specifier = ">=1.9.0" },
-    { name = "xonsh", editable = "../xonsh" },
+    { name = "xonsh", specifier = ">=0.23.0" },
 ]
 subints = [{ name = "msgspec", marker = "python_full_version >= '3.14'", specifier = ">=0.21.0" }]
 sync-pause = [{ name = "greenback", marker = "python_full_version == '3.13.*'", specifier = ">=1.2.1,<2" }]
@@ -870,61 +872,15 @@ wheels = [
 
 [[package]]
 name = "xonsh"
-source = { editable = "../xonsh" }
+version = "0.23.2"
-
+source = { registry = "https://pypi.org/simple" }
-[package.metadata]
+sdist = { url = "https://files.pythonhosted.org/packages/60/e5/2dfa99e21a8118bed0e73ed50e91962fdad01b900e23497064e8810b03b5/xonsh-0.23.2.tar.gz", hash = "sha256:633608c8292938af0f242f05326cc2912f25fa72bd808824ab0534a6df304402", size = 1030659, upload-time = "2026-04-26T19:28:40.744Z" }
-requires-dist = [
+wheels = [
-    { name = "click", marker = "extra == 'full'" },
+    { url = "https://files.pythonhosted.org/packages/53/0d/bf7869dd57b40888ea1da8fc88f70d8e94ec2f8ee236ea4c22a757593235/xonsh-0.23.2-py311-none-any.whl", hash = "sha256:a38dd84e23e97fc42e0156c80024b3449474dfcbb6c3a344bd38c45a2b2de44d", size = 756215, upload-time = "2026-04-26T19:28:38.875Z" },
-    { name = "coverage", marker = "extra == 'test'", specifier = ">=5.3.1" },
+    { url = "https://files.pythonhosted.org/packages/f7/9f/b1bb0c15bf2120469c94b062f4b854588370ab94c7a1679c84ff646bf50b/xonsh-0.23.2-py312-none-any.whl", hash = "sha256:190a348fa19774de8e697af5f44c9adb95aca687fa475b31dda23d1a3462a3c6", size = 756224, upload-time = "2026-04-26T19:28:39.17Z" },
-    { name = "distro", marker = "sys_platform == 'linux' and extra == 'full'" },
+    { url = "https://files.pythonhosted.org/packages/83/23/8e037579ac86d8f266b4116338f902eab04175b88574a6438ee739dd3084/xonsh-0.23.2-py313-none-any.whl", hash = "sha256:4ebbf42a94f505d25694f154556ca0caa149a3f59870ec850bd13ad8df519dce", size = 756728, upload-time = "2026-04-26T19:28:39.493Z" },
-    { name = "distro", marker = "extra == 'linux'" },
+    { url = "https://files.pythonhosted.org/packages/05/ec/090300d9c5f14f58b5a684302f43535457f733a62f11673aa3ac38460717/xonsh-0.23.2-py314-none-any.whl", hash = "sha256:5efcd0f6db8f9f1dace256de2c04c3c044f2d86b48434187c43a69d602283a9e", size = 756767, upload-time = "2026-04-26T19:28:37.218Z" },
-    { name = "furo", marker = "extra == 'doc'" },
-    { name = "gnureadline", marker = "sys_platform == 'darwin' and extra == 'full'" },
-    { name = "gnureadline", marker = "extra == 'mac'" },
-    { name = "matplotlib", marker = "extra == 'doc'" },
-    { name = "myst-parser", marker = "extra == 'doc'" },
-    { name = "numpydoc", marker = "extra == 'doc'" },
-    { name = "pre-commit", marker = "extra == 'dev'" },
-    { name = "prompt-toolkit", marker = "extra == 'bestshell'", specifier = ">=3.0.29" },
-    { name = "prompt-toolkit", marker = "extra == 'ptk'", specifier = ">=3.0.29" },
-    { name = "prompt-toolkit", marker = "extra == 'test'", specifier = ">=3.0.29" },
-    { name = "psutil", marker = "extra == 'doc'" },
-    { name = "pygments", marker = "extra == 'bestshell'", specifier = ">=2.2" },
-    { name = "pygments", marker = "extra == 'pygments'", specifier = ">=2.2" },
-    { name = "pygments", marker = "extra == 'test'", specifier = ">=2.2" },
-    { name = "pyperclip", marker = "extra == 'ptk'" },
-    { name = "pyte", marker = "extra == 'test'", specifier = ">=0.8.0" },
-    { name = "pytest", marker = "extra == 'test'", specifier = ">=7" },
-    { name = "pytest-cov", marker = "extra == 'test'" },
-    { name = "pytest-mock", marker = "extra == 'test'" },
-    { name = "pytest-rerunfailures", marker = "extra == 'test'" },
-    { name = "pytest-subprocess", marker = "extra == 'test'" },
-    { name = "pytest-timeout", marker = "extra == 'test'" },
-    { name = "pyzmq", marker = "extra == 'doc'" },
-    { name = "re-ver", marker = "extra == 'dev'" },
-    { name = "requests", marker = "extra == 'test'" },
-    { name = "restructuredtext-lint", marker = "extra == 'test'" },
-    { name = "runthis-sphinxext", marker = "extra == 'doc'" },
-    { name = "setproctitle", marker = "sys_platform == 'win32' and extra == 'full'" },
-    { name = "setproctitle", marker = "extra == 'proctitle'" },
-    { name = "sphinx", marker = "extra == 'doc'", specifier = ">=3.1" },
-    { name = "sphinx-autobuild", marker = "extra == 'doc'" },
-    { name = "sphinx-prompt", marker = "extra == 'doc'" },
-    { name = "sphinx-reredirects", marker = "extra == 'doc'" },
-    { name = "sphinx-sitemap", marker = "extra == 'doc'" },
-    { name = "tomli", marker = "extra == 'dev'" },
-    { name = "tornado", marker = "extra == 'doc'" },
-    { name = "ujson", marker = "extra == 'full'" },
-    { name = "virtualenv", marker = "extra == 'test'", specifier = ">=20.16.2" },
-    { name = "xonsh", extras = ["bestshell"], marker = "extra == 'doc'" },
-    { name = "xonsh", extras = ["bestshell"], marker = "extra == 'test'" },
-    { name = "xonsh", extras = ["doc", "test"], marker = "extra == 'dev'" },
-    { name = "xonsh", extras = ["ptk", "pygments"], marker = "extra == 'full'" },
 ]
-provides-extras = ["ptk", "pygments", "mac", "linux", "proctitle", "full", "bestshell", "test", "dev", "doc"]
-
-[package.metadata.requires-dev]
-dev = [{ name = "xonsh", extras = ["dev"] }]
 
 [[package]]
 name = "zipp"