cli: force UTF-8 stdio on startup + use platform-native fake path in run-update test

Fixes two Windows-only CLI regressions:

- UnicodeEncodeError: 'charmap' codec can't encode character
  '\U0001f30d' — Windows console stdout defaults to the ANSI code
  page (cp1252) which can't encode the emoji / box-drawing
  characters abxpkg prints (🌍, 📦, —, …). Added _force_utf8_stdio
  which reconfigure()s sys.stdout / sys.stderr to UTF-8
  (with errors='replace' as belt-and-suspenders), wired into both
  main() and abx_main() entrypoints. Unix stdio is already
  UTF-8 so this is a no-op there. Fixes
  test_abxpkg_version_runs_without_error and
  test_version_report_includes_provider_local_cached_binary_list.
- test_run_update_skips_env_for_the_update_step: the hardcoded
  Path("/tmp/fake-bin") literal stringifies differently on Windows
  (\tmp\fake-bin) vs POSIX. Use tmp_path / 'fake-bin' on both
  sides of the assertion so the comparison holds on every platform.

Author: claude

abxpkg/cli.py

@@ -549,6 +549,26 @@ def _console_for_stream(*, err: bool):
     )
 
 
+def _force_utf8_stdio() -> None:
+    """Reconfigure ``sys.stdout`` / ``sys.stderr`` to UTF-8 at CLI startup.
+
+    Windows console streams default to the ANSI code page (``cp1252``
+    on US-English hosts), which can't encode the emoji / box-drawing
+    characters abxpkg prints (``🌍``, ``📦``, ``—`` …). Without this,
+    the first such character raises ``UnicodeEncodeError`` and the CLI
+    crashes mid-output. Unix stdio is already UTF-8 by default so this
+    is effectively a no-op there; the ``errors='replace'`` fallback is
+    belt-and-suspenders in case the platform refuses UTF-8 outright.
+    """
+    for stream in (sys.stdout, sys.stderr):
+        reconfigure = getattr(stream, "reconfigure", None)
+        if reconfigure is not None:
+            try:
+                reconfigure(encoding="utf-8", errors="replace")
+            except (OSError, ValueError):
+                pass
+
+
 def _echo(message: Any, *, err: bool = False) -> None:
     console = _console_for_stream(err=err)
     if console is not None:
@@ -1849,6 +1869,7 @@ def _expand_bare_bool_flags(argv: list[str]) -> list[str]:
 
 
 def main() -> None:
+    _force_utf8_stdio()
     cli(_expand_bare_bool_flags(sys.argv[1:]))
 
 
@@ -1939,6 +1960,7 @@ def abx_main() -> None:
     surface area — every option is still documented and parsed exactly
     once, by ``abxpkg`` itself.
     """
+    _force_utf8_stdio()
     argv = list(sys.argv[1:])
     pre, rest = _split_abx_argv(argv)
     # Expand bare bool flags only in the pre-binary-name slice; rest is

tests/test_cli.py

@@ -542,9 +542,11 @@ def exec(self, bin_name, cmd=(), capture_output=False):
                 "",
             )
 
+    fake_bin_path = tmp_path / "fake-bin"
+
     class FakeRunBinary:
         def __init__(self):
-            self.loaded_abspath = Path("/tmp/fake-bin")
+            self.loaded_abspath = fake_bin_path
             self.loaded_version = SemVer("1.2.3")
             self.loaded_binprovider = FakeLoadedProvider("env")
             self.binproviders = []
@@ -585,7 +587,7 @@ def update(self, binproviders=None, dry_run=None, no_cache=None):
     assert calls == [
         ("load", (False,)),
         ("update", (("brew",), False, False)),
-        ("exec", ("brew", "/tmp/fake-bin", ("--version",), False)),
+        ("exec", ("brew", str(fake_bin_path), ("--version",), False)),
     ]