The T03 smoke asserted `play-lane` visible on mount, but those per-lane
buttons only render after a preview-compression run populates
`batch.lanes` (usePreviewCompression keeps batch null until run(); there
is no mount auto-run). The smoke intentionally does not drive a
compression cascade, so `play-lane` can never appear -> the E2E added in
#5727 failed all 3 retries (E2E Tests 4/9). Anchor on the always-present
`play-input` panel, which proves the studio body mounted without needing
async lane data.
31fd6dddbf