#3326 changed loadSession's INFLIGHT + idle render calls from bare
renderMessages() to renderMessages(sameSessionForceReload?{preserveScroll:true}:undefined),
and added reload-width-hint handling inside _ensureMessagesLoaded. Updated 5
source-pinning tests to match the new (behaviorally-equivalent) call form:
- test_regressions / test_issue2341: match 'renderMessages(' call form
- test_parallel_session_switch: match call form + widen 600->850 block window
- test_issue1690: assert the CONDITIONAL preserveScroll (cross-session still bottom-pins)
- test_issue3162: widen _ensureMessagesLoaded slice 2000->2600
