A failed step's output can be missing from its job's log

CI #599 (run_01m5h371vye69bdgs85r7bb23w), first attempt, job Rust (3), step 8 'Tests' (cargo test -p g1t-repos -p g1t-actions-service --locked --quiet): exited 1 after 26s with sccache showing 0 compilations, and the log holds only the step's header and '##[error]Process completed with exit code 1' - none of the command's output, though a failing cargo test prints its failures. The rerun (attempt 2) passed and its output arrived. This ran on the runner after #336 (log uploads moved to a background thread; a step's state goes ahead of its log; done waits 30s then drops what is left). Find whether the runner dropped the step's tail (drain cutoff, a lost final batch when the process exits, step/attempt mix-up on the uploader) or the output never existed, and make a failing step's output always arrive.