Replace the bare-instance, wall-clock-bound unit test with two invariants run
through the real lifecycle hooks: a task end returns while the process-wide
flush barrier is parked (later task ends coalesce into one extra pass), and the
background worker runs under the finishing turn's profile. The existing runtime
tests that read the store right after a hook now join the worker first, and the
daily-package test joins after its first session so the package forms where the
test expects it.
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