#30483 scripts/measure: fresh-home launch of a PR head on a fleet console worker

Rulebook (Chief area): a PR that changes Chief code lands only after, among other things, "a fresh-home launch passes on a fleet Mac". Until now only a published nightly DMG got one (nightly-next-launch-smoke.yml), so a Chief PR had no way to meet that rule before landing.

scripts/measure/fresh-home-launch.sh builds a tagged Debug app at ref= (in its own worktree, so a PR head that predates this script can be launched) the way crash-gate.sh does, then runs the nightly's own harness, scripts/ci/fresh_home_launch_smoke.py --app: an empty HOME, no defaults, Home must render, and the app must stay up for 30 s. Its exit code is the smoke's (0 passed, 1 failed, 3 could not run).

cmux-ci run --class exclusive --label measure --display \
  --script scripts/measure/fresh-home-launch.sh --ref <main sha> --arg=ref=<PR head sha> \
  --artifact .build/fresh-home-launch/report.tgz --timeout 3600

It runs only on demand. It adds no CI gate, job or workflow.

Observed / Not run

• Observed: bash -n passes. The prepush gate passes.
• Not run: the first fleet run, since exclusive steps run only from scripts already on the base. It runs right after landing, for #30458, and the result goes on that PR.

Risk: low (an on-demand measure script).

Changelog

none

Agent session: agent session

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