The runtime's transition trace — one append-only list shared by every handle of a runtime. §0 conformance for §7D is judged on these lines: identical per-handle transition sequences against the shared examples/subagent-* fixtures.
examples/subagent-*
Append one trace line.
All trace lines, in order.
@spec add(pid(), String.t()) :: :ok
@spec all(pid()) :: [String.t()]