Exercise 2: What a Downstream Service Needs From traceparent — Possible Solution
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Given: traceparent: 00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01

Explanation:

Of the header's four dash-separated parts -- version, trace ID,
parent span ID, and trace flags -- a downstream service needs two of
them specifically to correctly create its own span as a child of the
right parent:

1. The trace ID (4bf92f3577b34da6a3ce929d0e0e4736) -- this is what the
   downstream service must reuse UNCHANGED on its own newly created
   span, so that its span is recognized as belonging to the same
   overall trace as everything upstream, rather than starting a
   disconnected trace of its own.

2. The parent span ID (00f067aa0ba902b7) -- this is the ID of
   whichever span made the call that's now arriving at this
   downstream service. The downstream service records this value as
   its OWN new span's parent span ID, which is exactly what lets the
   resulting trace tree (as visualized in Jaeger) correctly place the
   new span as a child underneath the specific span that called it,
   rather than as an unconnected sibling or a second root.

The version and trace flags fields matter for the protocol itself
(format versioning, sampling decisions) but aren't what determines
correct parent-child placement in the tree -- that placement comes
specifically from correctly reading and reusing the trace ID and
parent span ID together.

WHY THIS WORKS AS AN ANSWER
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This identifies the two specific fields (trace ID and parent span ID)
that actually determine correct tree placement, distinguishing them
from the other two fields that serve a different purpose, rather than
vaguely stating "it needs the header."