discover-store-preview mocked src/stores/feed via mock.module, which bun
applies process-globally: with workers reused across test files, every file
that later shared a worker imported the stub (fetchEpisodes only) and failed
with 'addFeed is not a function' — ~35 tests, drifting run to run with worker
scheduling. Rewrote the test against the REAL feed store and a local gated
Bun.serve server (repo-dominant harness), importing the discover store via a
query-suffixed specifier so a sibling discover-store mock cannot leak in.
Full suite: 215 pass, 0 fail (baseline: 194).
