Addresses the review on #243. The original change interpolated the last
traceback frame into an `err_desc` string used in two places, and the second
one was the problem: `errors.execution_error` is sent back over the mesh, so
an absolute install path went out over RF and spent airtime on the error
path, where retries are most likely.
logger.exception() puts the full traceback in the log instead of just one
frame, which is strictly more than the original wanted, and the RF reply goes
back to str(e). That also removes the `list(tb.stack)[-1]` IndexError on an
empty stack, since the frame handling is gone entirely.
Tests cover both halves: the failure is logged via exception(), and the reply
carries only the exception text with no filesystem path.
CHANGELOG entry moves under the existing `## [Unreleased]` / `### Fixed`.
agessaman
cf26da652d