diff --git a/requirements/server.txt b/requirements/server.txt
index 6c7350fb1..dc51d02e4 100644
--- a/requirements/server.txt
+++ b/requirements/server.txt
@@ -11,3 +11,7 @@ fastapi>=0.100.0
 uvicorn[standard]>=0.24.0
 websockets>=12.0
 python-multipart>=0.0.6
+
+# --- LLM provider runtime (unconditionally imported by provider_core) ---
+loguru>=0.7.3,<1.0.0
+json-repair>=0.57.0,<1.0.0
diff --git a/scripts/start_web.py b/scripts/start_web.py
index 0eb41e402..291528c58 100644
--- a/scripts/start_web.py
+++ b/scripts/start_web.py
@@ -78,6 +78,8 @@ def _spawn(
         "stderr": subprocess.STDOUT,
         "text": True,
         "bufsize": 1,
+        "encoding": "utf-8",
+        "errors": "replace",
     }
     if os.name == "nt":
         kwargs["creationflags"] = subprocess.CREATE_NEW_PROCESS_GROUP  # type: ignore[attr-defined]