fix: save and load chat conversations as UTF-8

The interactive proxy chat /save command wrote conversations with
json.dump's default ensure_ascii=True and no file encoding, so non-ASCII
content (any non-English message, emoji) was stored as unreadable \uXXXX
escapes, and /load read the file with the platform default encoding.

Write with ensure_ascii=False and open both /save and /load as UTF-8 so
conversations are stored readably and round-trip on every platform,
matching how the rest of the codebase persists JSON.

litellm/proxy/client/cli/commands/chat.py

@@ -301,8 +301,8 @@ def _save_conversation(console: Console, messages: list[dict[str, str]], command
         filename += ".json"
 
     try:
-        with open(filename, "w") as f:
-            json.dump(messages, f, indent=2)
+        with open(filename, "w", encoding="utf-8") as f:
+            json.dump(messages, f, indent=2, ensure_ascii=False)
         console.print(f"[green]Conversation saved to {filename}[/green]")
     except Exception as e:
         console.print(f"[red]Error saving conversation: {e}[/red]")
@@ -320,7 +320,7 @@ def _load_conversation(console: Console, command: str, system: str | None) -> li
         filename += ".json"
 
     try:
-        with open(filename, "r") as f:
+        with open(filename, "r", encoding="utf-8") as f:
             loaded: Final[_MessagesView] = {"messages": json.load(f)}
         console.print(f"[green]Conversation loaded from {filename}[/green]")
         return loaded["messages"]

tests/unit/proxy/client/cli/test_chat_commands.py

@@ -0,0 +1,27 @@
+from pathlib import Path
+
+from rich.console import Console
+
+from litellm.proxy.client.cli.commands.chat import (
+    _load_conversation,
+    _save_conversation,
+)
+
+
+def test_save_and_load_conversation_roundtrips_non_ascii(tmp_path: Path) -> None:
+    """/save writes readable UTF-8 (not \\uXXXX escapes) and /load reads it back on any locale."""
+    console = Console()
+    messages = [
+        {"role": "user", "content": "Café ☕ 東京"},
+        {"role": "assistant", "content": "日本語で返信します"},
+    ]
+    target = tmp_path / "conversation.json"
+
+    _save_conversation(console, messages, f"/save {target}")
+
+    saved = target.read_text(encoding="utf-8")
+    assert "東京" in saved
+    assert "\\u" not in saved
+
+    loaded = _load_conversation(console, f"/load {target}", system=None)
+    assert loaded == messages