SR-5: escape unencodable characters in the stdout wrapper

changelog.d/stdout-unencodable-escape.md

@@ -0,0 +1,4 @@
+- **Command output no longer crashes on a character the stream cannot encode.** `chock check` on a
+  Windows runner (stdout cp1252) raised `UnicodeEncodeError` on U+FFFD while printing eval results. The
+  stdout wrapper now retries with `backslashreplace` in the stream's encoding; text the encoding can
+  represent prints unchanged.

src/chock/pipe.py

@@ -23,7 +23,11 @@ def write(self, text: str) -> int:
         if self.closed_by_reader:
             return len(text)
         try:
-            return self._stream.write(text)
+            try:
+                return self._stream.write(text)
+            except UnicodeEncodeError:
+                encoding = getattr(self._stream, "encoding", None) or "ascii"
+                return self._stream.write(text.encode(encoding, "backslashreplace").decode(encoding))
         except OSError as exc:
             if not _is_broken_pipe(exc):
                 raise

tests/test_pipe_tolerance.py

@@ -117,3 +117,41 @@ def test_recompile_finishes_its_bookkeeping_when_the_reader_closes_early(tmp_pat
         f"just installed now fail every commit:\n{output}"
     )
     assert "index_freshness" not in output, f"INDEX.md was left stale by the truncated run:\n{output}"
+
+
+def test_unencodable_character_is_escaped_not_raised() -> None:
+    """IR-F18: U+FFFD on a cp1252 stream (Windows console) must not crash the command."""
+    raw = io.BytesIO()
+    stream = io.TextIOWrapper(raw, encoding="cp1252", errors="strict")
+    writer = PipeTolerantWriter(stream)
+
+    writer.write("ok � end")
+    writer.flush()
+
+    assert raw.getvalue() == b"ok \\ufffd end"
+
+
+def test_representable_text_is_written_unchanged() -> None:
+    raw = io.BytesIO()
+    writer = PipeTolerantWriter(io.TextIOWrapper(raw, encoding="cp1252", errors="strict"))
+
+    writer.write("café €")
+    writer.flush()
+
+    assert raw.getvalue() == "café €".encode("cp1252")
+
+
+def test_broken_pipe_on_the_escaped_retry_is_tolerated() -> None:
+    class _Cp1252ThenClosed(io.StringIO):
+        encoding = "cp1252"
+
+        def write(self, text: str) -> int:
+            if "�" in text:
+                raise UnicodeEncodeError("charmap", text, 0, 1, "undefined")
+            raise BrokenPipeError(32, "Broken pipe")
+
+    writer = PipeTolerantWriter(_Cp1252ThenClosed())
+
+    writer.write("ok � end")
+
+    assert writer.closed_by_reader