[DrunkOnJava]

Summary

rustup toolchain install failed once on full / build + real files / macos-26 / stable on #1483 at 1811752 with "could not download file from 'https://static.rust-lang.org/dist/channel-rust-stable.toml.sha256'", with nothing wrong in the code. rustup's own retries are over in seconds. #1491 put the install in one composite action, so one change now covers every job.

The install is tried three times, 20 s and 40 s apart, each failure leaving a warning. A toolchain that really can't be installed still fails the job, with an error, about a minute later.

The one other rustup download in CI, rustup component add rustfmt in ifcopenshell-validate, moves into that job's setup step as component: rustfmt, so it goes through the same retry.

Cache keys don't move: no toolchain and no environment variable changes, and Swatinem/rust-cache v2.9.3 hashes neither the action file nor the installed components. Every rust-cache key on this PR's CI run 42134631531 equals the same job's on main's run 42131995046, the IfcOpenShell job's included (v0-rust-ci-release-Linux-x64-cdee7d24-2ff012fc).

Refs #1457.

Verification

• The action's run block, run under bash --noprofile --norc -eo pipefail (as GitHub runs shell: bash) against a fake rustup, rustc and sleep:
  • 0 failures: exit 0, 1 install, no sleep.
  • 2 failures: exit 0, 3 installs, sleeps of 20 and 40, default set, 2 lines in GITHUB_ENV.
  • 3 and 9 failures: exit 1, 3 installs, the error annotation, no default set, nothing in GITHUB_ENV.
• actionlint exits 0.
• Not measured: a real download failure on a runner. tools/ci/check-workflows.py wasn't run locally (no PyYAML here); CI runs it.

No output, src/ or gate file changes, so no Measure.