docs(vector): correct _drive_local_coroutine suspension-guard comment (#926)

The prior comment claimed anyio.lowlevel.checkpoint() yields None and is
re-driven, but checkpoint() yields a non-None backend object (asyncio
Future / trio checkpoint) and so trips the RuntimeError guard. Clarify
that only a literal bare yield/yield None is re-driven; any real awaitable
is caught by the non-None guard. Comment-only; no behavior change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/vector/qdrant_client.py

@@ -126,14 +126,15 @@ def _drive_local_coroutine(coro: Coroutine[Any, Any, Any]) -> Any:
     thread dispatched by :func:`anyio.to_thread.run_sync` — is what moves that
     CPU work off the event loop.
 
-    A genuine suspension (a non-``None`` yield) would mean the backend started
+    A genuine suspension would mean the backend started doing real async I/O,
-    doing real async I/O, which a plain thread cannot drive correctly. Fail
+    which a plain thread cannot drive correctly. Any real awaitable yields a
-    loudly in that case rather than spin or silently mis-drive the coroutine.
+    non-``None`` object (an asyncio ``Future`` / a trio checkpoint), so the
-    A bare ``yield None`` (e.g. a hand-inserted ``anyio.lowlevel.checkpoint()``)
+    ``yielded is not None`` guard catches it and fails loudly rather than
-    is deliberately treated as a non-suspension and re-driven — consistent with
+    spinning or silently mis-driving the coroutine. Only a literal bare
-    the local backend being purely synchronous. If a qdrant adapter ever starts
+    ``yield`` / ``yield None`` is treated as a non-suspension and re-driven —
-    inserting real checkpoints, prefer wrapping it in network mode over relaxing
+    consistent with the local backend being purely synchronous. If a qdrant
-    this guard.
+    adapter ever starts inserting real checkpoints, prefer wrapping it in
+    network mode over relaxing this guard.
     """
     try:
         while True: