fix: bracket MemoryBank() with temp env to honor BYOK

server.py

@@ -108,8 +108,23 @@ def _has_memory_bank(cfg: dict) -> bool:
 
 
 def _build_memory_bank(path: str, *, openai_api_key: str) -> MemoryBank:
-    """Load the prebuilt bank; force embeddings to use the caller's key."""
-    bank = MemoryBank(store_dir=path)
+    """Load the prebuilt bank; force embeddings to use the caller's key.
+
+    MemoryBank.__init__ instantiates ``OpenAI()`` with no args, which raises
+    on the Space because OPENAI_API_KEY is not in the env. We bracket the
+    constructor with a temporary env mutation, then replace the client.
+    The mutation is safe because no coroutine yields between the set and
+    the constructor (single-threaded asyncio).
+    """
+    prev = os.environ.get("OPENAI_API_KEY")
+    os.environ["OPENAI_API_KEY"] = openai_api_key
+    try:
+        bank = MemoryBank(store_dir=path)
+    finally:
+        if prev is None:
+            os.environ.pop("OPENAI_API_KEY", None)
+        else:
+            os.environ["OPENAI_API_KEY"] = prev
     bank._client = OpenAI(api_key=openai_api_key)  # noqa: SLF001
     return bank