test(integration): address round-1 review — unify searchability helper

- Extract the duplicated `_document_is_searchable`/`_note_is_searchable`
  helpers into a shared, Playwright-free `tests/integration/_search_helpers.py`
  (`document_is_searchable`), used by both the plotly and sampling tests.
- Resolve the sampling Medium finding: `wait_for_vector_sync` now triggers the
  searchability path on `search_term` alone (matching the plotly variant)
  instead of requiring both `search_term` and `note_id`, removing the silent
  fall-through to the unreliable gauge-delta path.
- Tighten `_get_with_retry`'s `last_exc` annotation to `httpx.TransportError`.

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

tests/integration/_search_helpers.py

@@ -0,0 +1,43 @@
+"""Shared helpers for asserting vector-sync visibility in integration tests.
+
+Kept dependency-light (no Playwright) so both the multi-user-basic UI tests and
+the single-user sampling tests can import it.
+"""
+
+import json
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+async def document_is_searchable(
+    mcp_client, search_term: str, note_id: int | None = None
+) -> bool:
+    """Return True once a freshly-created document is retrievable.
+
+    Polls ``nc_semantic_search`` (hybrid: an exact unique term reliably matches
+    on the keyword side) and matches by ``note_id`` when provided, otherwise by
+    the term appearing in a result's title/excerpt. Transient errors return
+    False so callers can keep polling.
+    """
+    try:
+        search = await mcp_client.call_tool(
+            "nc_semantic_search",
+            arguments={"query": search_term, "limit": 10, "score_threshold": 0.0},
+        )
+    except Exception as e:  # transient transport/availability blip — keep polling
+        logger.debug("Semantic search poll failed: %s", e)
+        return False
+    if search.isError:
+        logger.debug("Semantic search poll error: %s", search)
+        return False
+
+    results = json.loads(search.content[0].text).get("results", [])
+    needle = search_term.lower()
+    for r in results:
+        if note_id is not None:
+            if r.get("id") == note_id and r.get("doc_type") == "note":
+                return True
+        elif needle in f"{r.get('title', '')} {r.get('excerpt', '')}".lower():
+            return True
+    return False