refactor: minor cleanup from final whoosh-compat migration review

- Update stale test comments in test_query.py that described string
  rewriting / raw-query fallback behavior that no longer exists post
  whoosh-compat migration; rename
  test_date_rewriting_applied_before_tantivy_parse to
  test_date_keyword_resolves_without_raising to match.
- views.py: move the local MultipleSearchQueryErrors import up into the
  existing local-import block near the top of list(), consistent with
  the other documents.search imports there, instead of importing it
  again inside the except SearchQueryError clause.
- test_api_search.py: assert response.status_code explicitly before
  indexing into response.data["results"] in
  test_search_added_previous_month_excludes_next_period_start, and tie
  the xfail marker to AssertionError instead of the incidental KeyError
  that indexing a 400 response's missing "results" key produced.

src/documents/tests/search/test_query.py

@@ -59,12 +59,13 @@ class TestParseUserQuery:
         settings.ADVANCED_FUZZY_SEARCH_THRESHOLD = 0.5
         assert isinstance(parse_user_query(query_index, raw_query, UTC), tantivy.Query)
 
-    def test_date_rewriting_applied_before_tantivy_parse(
+    def test_date_keyword_resolves_without_raising(
         self,
         query_index: tantivy.Index,
     ) -> None:
-        # created:today must be rewritten to an ISO range before Tantivy parses it;
-        # if passed raw, Tantivy would reject "today" as an invalid date value
+        # whoosh-compat's DateParserPlugin resolves "today" against the AST
+        # directly (no string rewrite to an ISO range happens anywhere in
+        # this pipeline); the emitted tantivy query must still build cleanly.
         with time_machine.travel(datetime(2026, 3, 28, 12, 0, tzinfo=UTC), tick=False):
             q = parse_user_query(query_index, "created:today", UTC)
         assert isinstance(q, tantivy.Query)
@@ -92,9 +93,10 @@ class TestParseUserQuery:
         self,
         query_index: tantivy.Index,
     ) -> None:
-        # parse_user_query falls back to the raw query on unexpected translation
-        # errors, but an InvalidDateQuery is intentional and must propagate so the
-        # view can return a 400 instead of silently parsing the raw (invalid) date.
+        # parse_user_query never falls back to the raw query string on a parse
+        # error — a bad date diagnostic from whoosh-compat always maps to an
+        # InvalidDateQuery and must propagate, so the view can return a 400
+        # instead of silently parsing the raw (invalid) date.
         with pytest.raises(InvalidDateQuery) as exc_info:
             parse_user_query(query_index, "created:202023", UTC)
         assert exc_info.value.field == "created"

src/documents/tests/test_api_search.py

@@ -731,7 +731,7 @@ class TestDocumentSearchApi(DirectoriesMixin, APITestCase):
             "which already quotes. CONFIRMED REGRESSION vs whoosh-compat "
             "migration; see task-10-report.md."
         ),
-        raises=KeyError,
+        raises=AssertionError,
     )
     def test_search_added_previous_month_excludes_next_period_start(self) -> None:
         """
@@ -769,6 +769,10 @@ class TestDocumentSearchApi(DirectoriesMixin, APITestCase):
             tick=False,
         ):
             response = self.client.get("/api/documents/?query=added:previous month")
+        assert response.status_code == 200, (
+            f"expected a successful search response, got {response.status_code}: "
+            f"{response.data!r}"
+        )
         results = response.data["results"]
 
         self.assertEqual(len(results), 1)

src/documents/views.py

@@ -2415,6 +2415,7 @@ class UnifiedSearchViewSet(DocumentViewSet):
         if not self._is_search_request():
             return super().list(request)
 
+        from documents.search import MultipleSearchQueryErrors
         from documents.search import SearchHit
         from documents.search import SearchQueryError
         from documents.search import TantivyBackend
@@ -2613,8 +2614,6 @@ class UnifiedSearchViewSet(DocumentViewSet):
             # User-fixable query error(s) (e.g. unparsable dates/numbers):
             # surface every offending field's message, not just the first,
             # so the user can fix them all in one round-trip.
-            from documents.search import MultipleSearchQueryErrors
-
             messages = (
                 [str(sub) for sub in e.errors]
                 if isinstance(e, MultipleSearchQueryErrors)