The TestRunJobSessionPersistence run_job tests shared a helper that returned
a positional list of patches; callers applied a hardcoded slice
(patches[0..N]). When the BSM-seam fix split one env patch into two, the list
grew and every caller's slice silently dropped resolve_runtime_provider off
the end. The tests still passed locally — a dev machine has ambient provider
state (seeded via the cron delivery-routing path's plugin discovery) that let
the real resolver succeed — but failed on CI's clean HOME where nothing seeds
a provider, so run_job raised AuthError and AIAgent was never constructed.
Fix: _run_job_patches is now a contextmanager that enters the whole patch
bundle via ExitStack and yields (fake_db, mock_agent_cls). A caller can no
longer drop a patch by index, so a future seam change can't reintroduce the
local-green/CI-red split. Behaviour and assertions unchanged; 577 cron tests
pass.
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