Adjust `test_shield_pause` for capsys backends

Under `main_thread_forkserver` the bootstrapping
hook switches to `--capture=sys`, so subactor
fd-level output (tree dumps, zombie-reaper msgs)
isn't captured per-test by pexpect. Gate those
expects behind a `no_capfd` check so the test
passes on both capture modes.

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

tests/devx/test_tooling.py

@@ -52,6 +52,8 @@ def test_shield_pause(
         ...,
         PexpectSpawner,
     ],
+    start_method: str,
+    request: pytest.FixtureRequest,
 ):
     '''
     Verify the `tractor.pause()/.post_mortem()` API works inside an
@@ -119,6 +121,21 @@ def test_shield_pause(
     # (above) and `end-of-('hanger'` (below).
     handle_out_of_order: bool = False
 
+    # XXX, when capfd is NOT used we don't expect to
+    # see the logging output from the subactor.
+    if (no_capfd := (start_method in [
+            'main_thread_forkserver',
+        ])
+    ):
+        opts = request.config.option
+        assert opts.spawn_backend == start_method
+        # ?XXX? i guess the `testdir` fixture "pretends to" reset
+        # this to the default 'fd'??
+        # assert opts.capture in [
+        #     'sys',
+        #     'no',
+        # ]
+
     if (
         handle_out_of_order
         and
@@ -128,10 +145,15 @@ def test_shield_pause(
          assert 'Relaying `SIGUSR1`[10] to sub-actor' in _before
 
     else:
-        expect(
+        _before = expect(
             child,
             'Relaying `SIGUSR1`\\[10\\] to sub-actor',
         )
+        # _before: str = assert_before(
+        #     child,
+        #     ["('hanger'",]  # uid line
+        # )
+        if not no_capfd:
             expect(
                 child,
                 # end-of-subactor's-tree delimiter
@@ -163,14 +185,19 @@ def test_shield_pause(
         _shutdown_msg,
         timeout=6,
     )
-    assert_before(
-        child,
-        [
+    expect_on_teardown: list[str] = [
         'raise KeyboardInterrupt',
+        'Root actor terminated',
+    ]
+    if not no_capfd:
+        expect_on_teardown += [
             # 'Shutting down actor runtime',
             '#T-800 deployed to collect zombie B0',
             "'--uid', \"('hanger',",
         ]
+    assert_before(
+        child,
+        expect_on_teardown,
     )