Improper use of Queue/Deque vs List

In most circumstances in branch, queue is used improperly. Queue should only be used in inbetween-scenarios where linear polling is required by design. Most methods should return List.

The issue names no files, tests, or entry points. Start by locating methods that expose Queue or Deque and determine which uses require linear polling; then define a scoped set of return-type changes and identify the callers and tests affected. Done requires an agreed scope and consistent List-based APIs where polling is not required.

Written by the indexing model from the issue text.