The example constructed e1 and e2 with newException but never raised
them, so the verified output showed no stackTrace fields, right after
prose promising automatic stack trace extraction and an example with a
full trace. Traces are captured at raise time, so the output was
accurate but the example looked broken.

Both exceptions are now raised and caught before logging, showing the
catch-and-collect pattern real code uses, and both entries in the
errors array carry full traces in the regenerated output. The section
intro now states when stackTrace appears: only for exceptions that
were actually raised, and only in builds with stack traces enabled
(debug, or --stacktrace:on with -d:release).