Run UDS-on-macOS CI leg, un-skip the example

UDS-on-macOS is otherwise un-exercised: the matrix
explicitly excludes the `macos-latest` + `uds` combo, so the
`uds_transport_actor_tree.py` example (skipped on macOS CI
since PR #460) is the only thing that ever touches that
path.

- drop the matrix `exclude` so the full suite runs with
  `--tpt-proto=uds` on `macos-latest`.
- un-skip the example on macOS+CI; with example-stderr
  surfacing in place a still-red run now yields the full
  traceback GH #473 asks for instead of a bare returncode
  assert.

Task-bullets 3 + 4 of GH #473.

Prompt-IO: ai/prompt-io/claude/20260702T155006Z_65bf9df5_prompt_io.md

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

.github/workflows/ci.yml

@@ -118,11 +118,6 @@ jobs:
           'tcp',
           'uds',
         ]
-        # https://github.com/orgs/community/discussions/26253#discussioncomment-3250989
-        exclude:
-          # don't do UDS run on macOS (for now)
-          - os: macos-latest
-            tpt_proto: 'uds'
 
     steps:
       - uses: actions/checkout@v4

tests/test_docs_examples.py

@@ -145,21 +145,6 @@ def test_example(
             'This test does run just fine "in person" however..'
         )
 
-    if (
-        'uds_transport_actor_tree' in ex_file
-        and
-        _friggin_macos
-        and
-        ci_env
-    ):
-        pytest.skip(
-            'UDS-transport example reliably fails on macOS CI.\n'
-            'UDS-on-macOS is otherwise un-exercised by the matrix\n'
-            '(no `tpt_proto=uds` macOS job), so this new example is\n'
-            'the first to surface it; the macOS UDS path needs\n'
-            'root-causing. Passes on Linux.'
-        )
-
     from .conftest import cpu_perf_headroom
 
     timeout: float = (