resolveCommandSpanName() converted command/method to a string with no type
check. json::Value::asString() throws for an array or an object, so a request
whose nested method is [] reached that conversion and the throw replaced a
clean tooBusy reply with internal.
The overloaded path is the only way in: fillHandler() returns tooBusy before
anything has read those fields, and every other exit either converted them
itself or means neither field is present. The effect is that the error code a
client receives depends on whether telemetry was compiled in, which telemetry
must never do.
The span now falls back to its existing unknown-command label when either
present field is not a string. The WebSocket path already validates both
fields before dispatch, so it is left alone.
The test drives a genuinely overloaded job queue, reading the threshold from
the production constant rather than copying it, and asserts the client still
gets tooBusy. It lives in the Beast tree because doCommand is daemon code and
needs jtx, which the gtest binary cannot reach.
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