e2e legibility: a scenario can die unnamed under set -eu

open   by a73x

Labels: backlog, test

M15 finding 7. When the failing pipeline is the mux client itself (e.g. sh being handed a socket path after a dispatch mutation), set -eu kills e2e.sh before the script reaches its own grep and e2e FAIL line — the run dies with sh's stderr and no scenario name. Observed live during Task 6's regrade-premise failure. The suite's catches are only legible when the failure reaches an assertion; the pipeline-death path bypasses them all. Wants a trap or per-scenario wrapper that names the scenario on ANY nonzero exit, not just assertion failures. See decisions.md M15.