fix(config): preserve literal $ in config values

.semversioner/next-release/patch-20260523000000000001.json

@@ -0,0 +1,4 @@
+{
+  "type": "patch",
+  "description": "Preserve literal `$` in config values (e.g. regex `file_pattern: \".*\\.md$\"`) by switching `_parse_env_variables` from `Template.substitute` to `Template.safe_substitute`; missing env vars are still detected explicitly via `Template.get_identifiers`. Fixes #2349."
+}

packages/graphrag-common/graphrag_common/config/load_config.py

@@ -83,12 +83,22 @@ def _get_parser_for_file(file_path: str | Path) -> Callable[[str], dict[str, Any
 
 
 def _parse_env_variables(text: str) -> str:
-    """Parse environment variables in the configuration text."""
-    try:
-        return Template(text).substitute(os.environ)
-    except KeyError as error:
-        msg = f"Environment variable not found: {error}"
-        raise ConfigParsingError(msg) from error
+    r"""Parse environment variables in the configuration text.
+
+    Uses ``Template.safe_substitute`` so that literal ``$`` characters in
+    config values (for example a regex anchor like ``.*\.md$`` in
+    ``file_pattern``) are preserved instead of raising ``ValueError``.
+    Missing env-var references are still detected explicitly via
+    ``get_identifiers`` so callers continue to see ``ConfigParsingError``
+    when a referenced placeholder has no value.
+    """
+    template = Template(text)
+    missing = [name for name in template.get_identifiers() if name not in os.environ]
+    if missing:
+        missing_names = ", ".join(f"'{name}'" for name in missing)
+        msg = f"Environment variable not found: {missing_names}"
+        raise ConfigParsingError(msg)
+    return template.safe_substitute(os.environ)
 
 
 def _recursive_merge_dicts(dest: dict[str, Any], src: dict[str, Any]) -> None:

tests/unit/load_config/test_load_config.py

@@ -155,3 +155,30 @@ def test_load_config():
     assert config_with_env_vars.nested_list[0].nested_int == 7
     assert config_with_env_vars.nested_list[1].nested_str == "list_value_2"
     assert config_with_env_vars.nested_list[1].nested_int == 8
+
+
+def test_load_config_preserves_literal_dollar_sign(tmp_path: Path) -> None:
+    """Bare ``$`` in a config value (e.g. regex anchor) must not crash the loader."""
+    config_path = tmp_path / "settings.yaml"
+    config_path.write_text(
+        'name: "regex value .*\\\\.md$"\n'
+        "value: 1\n"
+        "nested:\n"
+        '  nested_str: "ends with $"\n'
+        "  nested_int: 2\n"
+        "nested_list:\n"
+        '  - nested_str: "$$ is literal"\n'
+        "    nested_int: 3\n",
+        encoding="utf-8",
+    )
+
+    config = load_config(
+        config_initializer=TestConfigModel,
+        config_path=config_path,
+        load_dot_env_file=False,
+        set_cwd=False,
+    )
+
+    assert config.name == "regex value .*\\.md$"
+    assert config.nested.nested_str == "ends with $"
+    assert config.nested_list[0].nested_str == "$ is literal"