Records this session's investigation: walcompare's per-member floor
fix (f3c86a6) and the --force-snapshot soak scaffolding (9f4292d) were
built specifically to close 5.10a with direct live evidence, but hit
a new, separate blocker -- schedule_checkpoint() fires correctly but
its delaymgr-scheduled checkpoint_task_fn never executes in a live
deployment, so no snapshot is ever installed to test against. Task
5.10a stays open pending a dedicated delaymgr investigation.