fix(search): address PR #834 review findings

Resolve the latest PR-review comment on the verify-on-read tag-gate work:

- tests: stringify note IDs in test_verify_on_read.py so SearchResult.id
  matches production (scanner stringifies all IDs on write) — helper and the
  keeps/deleted/mixed/dedupe assertions (blocking).
- tests: make the unshared-file negative control a PDF so the drop is
  unambiguously "unshared", not a mime_type_filter mismatch.
- config: add Validator("VECTOR_SYNC_PDF_TAG", len_min=1) — an empty tag name
  would make find_files_by_tag("") misbehave in the verifier and scanner.
- verification: correct the _verify_files comment — two batch fetches (tag
  REPORT + EXCLUDED_TAGS lookup) are held under one semaphore slot; the
  pure-Python intersection runs outside it.
- tests: de-duplicate the minimal-PDF constant into a shared PDF_BYTES in
  tests/integration/conftest.py, imported by both integration modules.

Verified: ruff/format/ty/unit all green; the two integration modules
(10 tests) pass against a local Nextcloud (app-only, no MCP profile needed).

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

nextcloud_mcp_server/config.py

@@ -259,6 +259,8 @@ _dynaconf = Dynaconf(
         Validator("DOCUMENT_CHUNK_SIZE", gte=1),
         # Non-negative
         Validator("DOCUMENT_CHUNK_OVERLAP", gte=0),
+        # Non-empty strings
+        Validator("VECTOR_SYNC_PDF_TAG", len_min=1),
         # Enum constraints
         Validator("LOG_FORMAT", is_in=["text", "json"]),
         Validator(

nextcloud_mcp_server/search/verification.py

@@ -174,10 +174,14 @@ async def _verify_files(
 
     tag_name = get_settings().vector_sync_pdf_tag
 
-    # One batch fetch per search, holding a single semaphore slot (same
+    # Two batch fetches per search held under a single semaphore slot (same
     # backpressure rationale as _verify_news_items): the tagged-file REPORT
-    # plus optional Depth:infinity folder expansion — and the EXCLUDED_TAGS
-    # lookup — are one round-trip set, not one per result.
+    # (plus optional Depth:infinity folder expansion) and the EXCLUDED_TAGS
+    # lookup (get_excluded_file_paths, itself ~2×N concurrent calls). Both are
+    # batched once per search, not once per result, and the slot bounds them.
+    # The pure-Python intersection that builds tagged_ids/accessible runs
+    # *outside* the slot — it needs no Nextcloud round-trip (mirrors the
+    # post-fetch present_ids build in _verify_news_items).
     #
     # TODO(perf): if folder expansion dominates query latency, cache the
     # tagged-id set per user with a short TTL (mirroring the