Ship's gate policy stops paying for a durable runtime to assert it - #262

test_build_durable booted a module-scoped Postgres and a DBOS runtime, then
polled a 20s _wait loop, to make five assertions. Four of them were already
made elsewhere, cheaply, and the fifth was the platform's.

The two plan-gate tests duplicated test_build_plan_phase, which covers every
mode against the body's own phase methods with no runtime at all. The happy
path asserted an assembly whose parts each have a home: the journal's delivery
in test_build_journal, merge_when_ready's client behaviour in test_github, and
the pr.closed settlement in test_webhooks_pull_request — the file's own comment
already pointed at the last one. The claim test asserted that a gate resume
does not re-run the claim, but the claim is @subscribe(SCHEDULED) and a resume
emits no SCHEDULED, so that is the platform's event lifecycle, not ship's.

Only the repark survived with no other home, and it did not need the runtime
either: _approved_work re-enters the work gate when declare_merge_intent comes
back false. Twenty lines against the phase, same as its neighbours.

The suite loses the harness that made it flake — the uncommitted cancel holding
work_items row locks across a whole module, on the one background loop every
workflow body shares.