fix: keep the Windows launcher alive when stdout is cp1252

bootstrap/launch.py

@@ -39,6 +39,28 @@
 VERSION_PATTERN = re.compile(r"""^__version__\s*=\s*['"]([^'"]+)['"]""", re.MULTILINE)
 
 
+def _configure_stdio() -> None:
+    """Let a cp1252 Windows console print every character the child emits.
+
+    Hosted Windows runners start Python with the console code page, usually
+    cp1252. Child output is decoded with ``errors="replace"``, so a relayed
+    line can contain U+FFFD. Writing that character through a cp1252
+    ``sys.stdout`` raises ``UnicodeEncodeError`` and aborts the action.
+    UTF-8 encodes it.
+
+    A missing stream, a redirect that has no ``reconfigure``, or an
+    ``OSError`` / ``ValueError`` from the stream must not abort startup.
+    """
+    for stream in (sys.stdout, sys.stderr):
+        reconfigure = getattr(stream, "reconfigure", None)
+        if reconfigure is None:
+            continue
+        try:
+            reconfigure(encoding="utf-8", errors="replace")
+        except (OSError, ValueError):
+            continue
+
+
 def _env(name: str, default: str = "") -> str:
     return os.environ.get(name, default).strip()
 
@@ -82,6 +104,9 @@ def packaged_version(checkout: Path) -> str:
 
 
 def main() -> int:
+    # Before any print or relayed child line. The crash is a cp1252 stdout
+    # refusing U+FFFD; every later write goes through these two streams.
+    _configure_stdio()
     repo = Path(_env("SKILLSCOPE_REPO", ".") or ".").expanduser().resolve()
     command = _env("SKILLSCOPE_COMMAND")
     if not command:

tests/test_skillscope.py

@@ -1007,6 +1007,73 @@ def test_it_installs_from_the_action_checkout(self) -> None:
             with mock.patch.dict(os.environ, {"SKILLSCOPE_ACTION_PATH": str(root)}):
                 self.assertEqual(self.module.action_root(), root)
 
+    def test_a_cp1252_console_can_relay_the_replacement_character(self) -> None:
+        # Child stdout is decoded with errors="replace", so U+FFFD reaches
+        # sys.stdout.write. A cp1252 console raises UnicodeEncodeError there
+        # unless startup reconfigured the stream to UTF-8.
+        buffer = io.BytesIO()
+        stdout = io.TextIOWrapper(buffer, encoding="cp1252", errors="strict")
+        stderr = io.TextIOWrapper(io.BytesIO(), encoding="cp1252", errors="strict")
+        child = io.StringIO("hot kernel \ufffd\n")
+
+        class FakeProc:
+            def __init__(self) -> None:
+                self.stdout = child
+
+            def wait(self) -> int:
+                return 0
+
+        repo_root = Path(__file__).resolve().parent.parent
+        try:
+            with tempfile.TemporaryDirectory() as tmp:
+                with (
+                    mock.patch.object(self.module.sys, "stdout", stdout),
+                    mock.patch.object(self.module.sys, "stderr", stderr),
+                    mock.patch.object(self.module.subprocess, "Popen", return_value=FakeProc()),
+                    mock.patch.dict(
+                        os.environ,
+                        {
+                            "SKILLSCOPE_COMMAND": "behavioral",
+                            "SKILLSCOPE_ARGS": "",
+                            "SKILLSCOPE_STDIN": "",
+                            "SKILLSCOPE_REPO": tmp,
+                            "SKILLSCOPE_ACTION_PATH": str(repo_root),
+                            "GITHUB_OUTPUT": "",
+                            "GITHUB_STEP_SUMMARY": "",
+                        },
+                    ),
+                ):
+                    code = self.module.main()
+            self.assertEqual(code, 0)
+            self.assertEqual(stdout.encoding, "utf-8")
+            self.assertEqual(stdout.errors, "replace")
+            self.assertEqual(stderr.encoding, "utf-8")
+            self.assertIn("\ufffd".encode("utf-8"), buffer.getvalue())
+        finally:
+            stdout.close()
+            stderr.close()
+
+    def test_stdio_setup_survives_a_stream_that_cannot_be_reconfigured(self) -> None:
+        class RaisesOSError:
+            def reconfigure(self, **_kwargs: object) -> None:
+                raise OSError("console code page is locked")
+
+        closed = io.TextIOWrapper(io.BytesIO(), encoding="cp1252")
+        closed.close()
+        cases = (
+            (None, None),
+            (io.StringIO(), io.StringIO()),
+            (RaisesOSError(), RaisesOSError()),
+            (closed, closed),
+        )
+        for stdout, stderr in cases:
+            with self.subTest(stdout=type(stdout).__name__):
+                with (
+                    mock.patch.object(self.module.sys, "stdout", stdout),
+                    mock.patch.object(self.module.sys, "stderr", stderr),
+                ):
+                    self.module._configure_stdio()
+
 
 class TestSelection(unittest.TestCase):
     """What CI runs for a change, and what it is right to skip."""