Capture the decision to hold one rolling (media-time ↔ PDT) anchor — learned
from the first A/V track to obtain SourceBuffer ground truth and applied to all
selected tracks (incl. text) by per-segment PDT — replacing today's per-track
buffer pins, which are redundant under the no-skew assumption and can't anchor
text (no SourceBuffer). New decision doc live-presentation-anchor.md; resolves
the deferred single-rolling-anchor question in live-timeline-anchoring and
promotes [4] in live-presentation-modeling to presentation-level.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
