fix(qdrant): use get_collection for startup probe (multi-tenant safe, take 2)

Follow-up to PR #778 — `collection_exists()` is also denied by Qdrant
Cloud on a collection-scoped JWT, so the multi-tenant fix needs to go
one step further: use `get_collection(name)` (the underlying GET
`/collections/{name}` call) and treat a 404 `UnexpectedResponse` as
the "doesn't exist" signal. That endpoint is the only existence-probe
Qdrant permits on a collection-scoped JWT — listing or probing
collection metadata cluster-wide is a tenant-isolation boundary by
design.

Hit during Astrolabe Cloud smoke17 with the post-#778 image:

    qdrant_client.http.exceptions.UnexpectedResponse: 403 (Forbidden)
    raw response: {"error":"forbidden"}
    File "qdrant_client.py", line 84, in get_qdrant_client
        collection_present = await _qdrant_client.collection_exists(...)

Folds the existence check into the same `get_collection()` call that
already runs immediately afterward for dimension validation, so the
new path is also one fewer round-trip on the happy path.

Cold-start (collection genuinely missing) behavior is unchanged: 404
→ `collection_info` is None → fall through to `create_collection()`.
Whether `create_collection` succeeds is an orthogonal concern (managed
multi-tenant setups pre-provision collections externally; admin-key
single-tenant setups can create on the fly).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/vector/qdrant_client.py

@@ -3,6 +3,7 @@
 import logging
 
 from qdrant_client import AsyncQdrantClient, models
+from qdrant_client.http.exceptions import UnexpectedResponse
 from qdrant_client.models import Distance, VectorParams
 
 from nextcloud_mcp_server.config import get_settings
@@ -71,26 +72,33 @@ async def get_qdrant_client() -> AsyncQdrantClient:
 
         expected_dimension = embedding_service.get_dimension()
 
-        # Explicitly check if collection exists.
+        # Existence check folded into the get_collection() call.
         #
-        # Use `collection_exists(name)` (per-collection HEAD-style probe)
+        # In managed multi-tenant Qdrant Cloud setups, per-tenant JWTs are
-        # rather than `get_collections()` (cluster-wide list). In managed
+        # scoped to a single collection (`access: [{"collection": "...",
-        # multi-tenant Qdrant Cloud setups, per-tenant JWTs are scoped
+        # "access": "rw"}]`) and Qdrant denies the cluster-level meta
-        # to a single collection and `get_collections()` returns 403
+        # endpoints `GET /collections` (used by `get_collections()`) and
-        # Forbidden by design — listing other tenants' collections would
+        # `GET /collections/{name}/exists` (used by `collection_exists()`)
-        # be a security regression. `collection_exists` only requires
+        # with 403 Forbidden — by design, since listing or probing
-        # access to the named collection, which the tenant JWT has.
+        # collections cluster-wide is a tenant-isolation boundary.
-        logger.debug(f"Checking if collection '{collection_name}' exists...")
+        # `GET /collections/{name}` (the underlying call for
-        collection_present = await _qdrant_client.collection_exists(
+        # `get_collection()`) is the only existence-probe permitted on a
-            collection_name=collection_name
+        # collection-scoped JWT — it returns 200 with the collection
-        )
+        # detail on hit and 404 on miss.
+        logger.debug(f"Fetching collection '{collection_name}' details...")
+        collection_info = None
+        try:
+            collection_info = await _qdrant_client.get_collection(collection_name)
+        except UnexpectedResponse as exc:
+            if exc.status_code != 404:
+                raise
+            logger.debug(f"Collection '{collection_name}' not found (404).")
 
-        if collection_present:
+        if collection_info is not None:
             # Collection exists - validate dimensions
             logger.debug(
                 f"Collection '{collection_name}' found, validating dimensions..."
             )
-            collection_info = await _qdrant_client.get_collection(collection_name)
             # Handle both named vectors (dict) and legacy single vector
             vectors = collection_info.config.params.vectors
             if isinstance(vectors, dict):