Shell tests went red on my last push. test_network_diagnostics.bats sourced
its scripts through $REPO_DIR/scripts/diagnostics, a level the flatten
removed, so setup() failed and all 30 tests errored.
Latent rather than new: the previous run was green only because ci-mirror
aborted before the bats stage. Fixing the concurrency OOM let the gate reach
this suite for the first time since the flatten.
Grepped the tree for the removed scripts/ and single_use/ levels; this was
the last one in tracked code.
Also rewrites the two handoff docs around the units that remain.
CI_GREEN_SKIP=1 because this commit is the fix for the red baseline.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PJrqKERAo5QUeEHWS5Asgp
Diagnosing "Steam downloads are slow" kept pointing at the ISP because
every averaged measurement showed a steady ~170 Mbps. Sampling at 1s
instead of 5s showed that plateau does not exist: the link alternates
between ~450 Mbps bursts and multi-second stalls. Effective rate is
burst x duty_cycle, and only the second factor was wrong.
steam-download-duty.sh reports those two factors separately, which is
what the Steam UI cannot do. line-speed-probe.sh separates burst from
sustained throughput, because a single stream tops out near 180 Mbps on
this line and reads convincingly as ISP shaping when it is not — a
many-connection swarm reaches 986 Mbps with zero retransmits.
Arithmetic is extracted into pure helpers with main() behind a
BASH_SOURCE guard so the bats suite can source them without starting a
measurement. install.sh installs bats and links both scripts onto PATH.
Note: no CI workflow runs .sh/.bats tests, including the four shell
tests that predate this one, so the suite is manual-only for now.
