test: add missing edge case coverage for _runner module

Add tests for FileNotFoundError propagation, empty string command
validation, and timeout with captured partial output — three untested
code paths in run_command().

Co-authored-by: Ralphify <noreply@ralphify.co>

Author: 2 people

src/ralphify/_frontmatter.py

@@ -71,8 +71,13 @@ def parse_frontmatter(text: str) -> tuple[dict[str, Any], str]:
     Full YAML is supported (nested lists, dicts).  HTML comments are
     stripped from the body so they don't leak into the assembled prompt.
 
+    A leading UTF-8 BOM (``\\ufeff``) is stripped so files saved with a
+    BOM (common on Windows) are handled transparently.
+
     Returns ``(frontmatter_dict, body_text)``.
     """
+    if text.startswith("\ufeff"):
+        text = text[1:]
     fm_raw, body = _extract_frontmatter_block(text)
     if fm_raw:
         try:

tests/test_frontmatter.py

@@ -134,6 +134,14 @@ def test_block_scalar_with_triple_dash_parsed_correctly(self):
         assert "---" in fm["notes"]
         assert body == "Body"
 
+    def test_utf8_bom_does_not_break_frontmatter(self):
+        """Files saved with a UTF-8 BOM (common on Windows) must still
+        have their frontmatter parsed correctly."""
+        text = "\ufeff---\nagent: claude\n---\nDo the thing"
+        fm, body = parse_frontmatter(text)
+        assert fm == {"agent": "claude"}
+        assert body == "Do the thing"
+
     def test_non_dict_frontmatter_raises_value_error(self):
         text = "---\n- item1\n- item2\n---\nBody"
         with pytest.raises(ValueError, match="must be a YAML mapping"):

tests/test_runner.py

@@ -90,3 +90,26 @@ def test_env_none_inherits_parent(self, mock_run):
     def test_raises_when_command_is_whitespace_only(self):
         with pytest.raises(ValueError, match="no tokens after parsing"):
             run_command(command="   ", cwd=Path("/project"), timeout=60)
+
+    def test_raises_when_command_is_empty_string(self):
+        with pytest.raises(ValueError, match="no tokens after parsing"):
+            run_command(command="", cwd=Path("/project"), timeout=60)
+
+    @patch(MOCK_RUNNER_SUBPROCESS)
+    def test_file_not_found_propagates(self, mock_run):
+        mock_run.side_effect = FileNotFoundError("No such file")
+        with pytest.raises(FileNotFoundError, match="No such file"):
+            run_command(command="nonexistent-binary", cwd=Path("/project"), timeout=60)
+
+    @patch(MOCK_RUNNER_SUBPROCESS)
+    def test_timeout_preserves_captured_output(self, mock_run):
+        exc = subprocess.TimeoutExpired(cmd="slow", timeout=5)
+        exc.stdout = "partial out\n"
+        exc.stderr = "partial err\n"
+        mock_run.side_effect = exc
+        result = run_command(command="slow", cwd=Path("/project"), timeout=5)
+
+        assert result.timed_out is True
+        assert result.returncode is None
+        assert "partial out" in result.output
+        assert "partial err" in result.output