Challenge 1: Write a Message Definition — Possible Solution
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message Order {
  int32 id = 1;
  string customer_name = 2;
  repeated string item_names = 3;
}

WHY THIS WORKS AS AN ANSWER
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id and customer_name are plain scalar fields, numbered 1 and 2 —
deliberately kept within the 1-15 range this chapter flagged as more
efficiently encoded, appropriate since these are core, always-present
fields on every order.

item_names uses the repeated keyword, marking it as a list rather than
a single value — the proto3 equivalent of a JSON array of strings,
exactly matching the "repeated list of item_names" requirement.

Field number 3 continues sequentially after id and customer_name, with
no gaps or reused numbers — a reasonable, deliberate choice for a
message being defined for the first time, since there's no prior
schema history to avoid conflicting with yet.