Verified against ProPresenter 21.4: the legacy stage-display protocol
(ptl 610 — the only version PP21 accepts; newer values get 'out of
date') omits stage objects it predates, so a timecode field labeled LTC
never appears in any layout's frame list, and no timecode messages were
observed while idle. Fallback: an unknown uid streaming timecode-shaped
text (a fourth :FF group; not any configured timer's uuid) is bound as
LTC after two advancing samples, and that binding survives layout
refreshes. pp-timers-mock gains --ltc-unlisted to exercise the path.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>