fix(viz_routes): address PR #767 review — param parity + always-on page_number

- Replace bare int() casts for start/end/context_chars in chunk_context_endpoint
  with _parse_int_param, matching visualization.py bounds (0–10M for offsets,
  0–10K for context_chars), and add the missing end > start guard.
- Initialize page_number from chunk_context.page_number so non-file doc_types
  surface it; include page_number, chunk_index, and total_chunks unconditionally
  in the response. Only highlighted_page_image stays gated on its own truthiness.
- Add a chunk_index forwarding regression test that asserts the new kwargs reach
  get_chunk_with_context and appear in the response payload.

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

tests/unit/test_management_chunk_context_endpoint.py

@@ -259,6 +259,58 @@ class TestChunkContextCredentialPath:
             assert "failed to fetch chunk context" in data["error"].lower()
 
 
+class TestChunkContextParameterForwarding:
+    """Verify new chunk_index / total_chunks query params reach the lookup.
+
+    Regression guard for PR #767: the whole point of the fix is that callers
+    pass chunk_index, and it must arrive at get_chunk_with_context as the
+    primary Qdrant lookup key.
+    """
+
+    def test_chunk_index_and_total_chunks_forwarded(self):
+        mock_nc_client = _make_mock_nc_client()
+        mock_ctx = _make_mock_chunk_context()
+        mock_ctx.chunk_index = 7
+        mock_ctx.total_chunks = 10
+
+        with (
+            patch(
+                "nextcloud_mcp_server.api.visualization.validate_token_and_get_user",
+                new_callable=AsyncMock,
+                return_value=("testuser", True),
+            ),
+            patch(
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
+                return_value=mock_nc_client,
+            ),
+            patch(
+                "nextcloud_mcp_server.api.visualization.get_chunk_with_context",
+                new_callable=AsyncMock,
+                return_value=mock_ctx,
+            ) as mock_get_chunk,
+        ):
+            app = create_test_app()
+            client = TestClient(app)
+            response = client.get(
+                "/api/v1/chunk-context?doc_type=note&doc_id=42"
+                "&start=0&end=10&chunk_index=7&total_chunks=10",
+                headers={"Authorization": "Bearer test-token"},
+            )
+
+            assert response.status_code == 200
+            kwargs = mock_get_chunk.await_args.kwargs
+            assert kwargs["chunk_index"] == 7
+            assert kwargs["total_chunks"] == 10
+
+            data = response.json()
+            assert data["chunk_index"] == 7
+            assert data["total_chunks"] == 10
+            # page_number must be present even when None (frontend may scroll
+            # by it for non-file doc types)
+            assert "page_number" in data
+
+
 class TestChunkContextConfigErrors:
     """Tests for configuration failure paths."""