Deferred review findings from PR #12128: fix(ci): retry transient E2E build artifact download failures once (#12125)

Verified review findings from PR #12128 by qwen-code-dev-bot whose fixes lie outside that PR's footprint, deferred by the autofix loop for follow-up. Each rc: item links back to its original review comment. A maintainer or the PR author can turn any item into its own issue/PR and apply the ready-for-agent flow to that issue — nothing here is scheduled automatically.

• ic:5722188466 .github/workflows/e2e.yml: F1 verified real: none of the four 'Download build artifact (retry)' steps carries timeout-minutes, and e2e-test-macos / isolated-nightly have no job-level ceiling (GitHub default 360 min), so a blackholed-route hang landing on the retry can hold a runner for hours — the maintainer's leg-B3 probe proved that hang class is reachable. Deferred because the maintainer explicitly scoped it out of this PR ('does not block this PR', 'a natural follow-up'). Fix sketch from the report: copy timeout-minut