fix(channels): persist runtime configuration as UTF-8 (#5803)

Co-authored-by: Zhangchenhao-111 <285911435+Zhangchenhao-111@users.noreply.github.com>

backend/app/channels/runtime_config_store.py

@@ -46,6 +46,7 @@ class ChannelRuntimeConfigStore:
     def _save(self) -> None:
         fd = tempfile.NamedTemporaryFile(
             mode="w",
+            encoding="utf-8",
             dir=self._path.parent,
             suffix=".tmp",
             delete=False,

backend/tests/test_channel_runtime_config_encoding.py

@@ -0,0 +1,35 @@
+"""Runtime channel configuration must round-trip independently of host locale."""
+
+import json
+
+import pytest
+
+from app.channels import runtime_config_store
+
+
+@pytest.mark.parametrize(
+    ("locale_encoding", "relay_url"),
+    [
+        ("cp1252", "wss://relay.example/caf\u00e9"),
+        ("gbk", "wss://relay.example/\u804a\u5929"),
+        ("cp1252", "wss://relay.example/\u804a\u5929"),
+    ],
+)
+def test_runtime_config_round_trips_non_ascii_with_legacy_locale(tmp_path, monkeypatch, locale_encoding, relay_url):
+    named_temporary_file = runtime_config_store.tempfile.NamedTemporaryFile
+
+    def locale_temporary_file(*args, **kwargs):
+        # Simulate a legacy host default only when the writer omits encoding.
+        kwargs.setdefault("encoding", locale_encoding)
+        return named_temporary_file(*args, **kwargs)
+
+    monkeypatch.setattr(runtime_config_store.tempfile, "NamedTemporaryFile", locale_temporary_file)
+    path = tmp_path / "channels" / "runtime-config.json"
+    config = {"enabled": True, "relay_url": relay_url}
+    store = runtime_config_store.ChannelRuntimeConfigStore(path)
+
+    store.set_provider_config("buzz", config)
+
+    assert json.loads(path.read_text(encoding="utf-8")) == {"buzz": config}
+    reloaded = runtime_config_store.ChannelRuntimeConfigStore(path)
+    assert reloaded.get_provider_config("buzz") == config