Follow-up rework on the #51627 cherry-pick:
- Guard the 5th wake check (parent-mentioned-bot, #24848) against a None
parent_text — _fetch_thread_parent_text is typed to return str but tests
(and defensive callers) can surface None; 'in None' raised TypeError.
- Drop the PR's fixture-level _fetch_thread_parent_text/_fetch_thread_context
AsyncMocks from TestThreadReplyHandling/TestAssistantThreadLifecycle: main's
#24848 tests exercise the real parent-text path via conversations_replies
side effects, and the blanket mocks broke them.
- _resolve_user_is_bot reworked to the workspace-scoped (team_id, user_id)
cache key introduced by the multi-workspace name cache on main.
7e42f0143c