WithTrace found a line's span with Span::current(), which asks the
thread's default dispatcher; inside an event under a scoped subscriber
(with_default), tracing's re-entrancy guard answers with none, so every
line went out without trace_id and span_id. Production, on the global
dispatcher, was not affected, but the log test had to go global for it.
The JSON layer now carries a small layer of its own that keeps the
subscriber it is registered with (on_register_dispatch, a weak handle),
and the formatter takes the registry's current span from its own
context and asks tracing-opentelemetry for its context through that
handle (get_otel_context), with no dispatcher lookup. The log test runs
scoped again; with the old formatter it fails for want of the ids.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RqkrVDqdiQEMWAkNGQ2tYA
rays
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