Address PR #2093 review feedback (Miga, Rames D Jusso):
- The walker treated a repeating nested timeline (total > single) as an
opaque interval and never descended into it, so a tl.call() living
inside one would slip past hasTimelineCall detection entirely — the
"any tl.call() disqualifies" claim wasn't quite literal. Now recurses
for detection purposes even when the span is already opaque; the
parent-level interval still dominates for frame-animated-marking, so
this only widens what counts as "has a call()," never narrows the
existing interval coverage.
- Restored the totalDuration() vs duration() rationale comment that got
dropped when the tl.call() detection comment was added above it.