Replaces the pre-hexagonal scheduled-task implementation with a slice
built to the layering spec: a pure domain (two aggregates, two state
machines, the policy value object), output ports it declares itself,
SQL/launcher/thread adapters implementing them under `app/adapters/`,
and a composition root that is the one place any of them is
instantiated.
The old implementation mixed all of that into `app/scheduler/service.py`
and a router that reached straight into repositories, so the rules that
matter -- overlap policy, lease handling, which write owns which
timestamp -- were only reachable through a live database. They are now
unit-assertable on in-memory fakes, with the contract suite running each
port against both the fake and real sqlite, and the concurrency
invariants pinned by dedicated race tests.
Two bugs the old shape hid are fixed on the way: a completion hook that
replayed a stale snapshot and rolled back the launch write, and a
corrupt stored row surfacing to the client as a 4xx.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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