ci: drop the macOS jobs

[marc0olo]

Follow-up to the discussion on #434. Removes the three macOS CI jobs and the now-unused provision-darwin.sh.

They have never caught anything Linux didn't

Every completed run of the three workflows (140 runs, 2026-07-27 → 08-26):

Workflow	Runs	pass/pass	fail/fail	cancelled	mac failed, linux passed
frontend.yml	60	51	3	4	0
backend-rust.yml	40	35	2	3	0
backend-motoko.yml	40	38	2	0	0

All 7 real failures failed on both platforms. The two apparent frontend divergences were success/cancelled and cancelled/success — artifacts of cancel-in-progress: true, not signal.

Coverage is preserved

Each macOS job ran a command block byte-identical to its Linux counterpart. Verified by hashing the run: bodies of the non-provisioning steps before deleting:

frontend.yml        linux 2518a70671d5  ==  mac 2518a70671d5
backend-rust.yml    linux ff569b94f041  ==  mac ff569b94f041
backend-motoko.yml  linux fa2141c56e44  ==  mac fa2141c56e44

The only differences between each pair were runs-on, the provision script, and the step name. The surviving Linux jobs execute exactly what the deleted jobs did — nothing to port over.

There is also little platform-specific surface to lose. The frontend package is portable TypeScript (@noble/* is pure JS, hashing goes through WebCrypto, IndexedDB is stubbed with fake-indexeddb); the Rust crates build to wasm32-unknown-unknown. The one genuinely platform-specific component under test was the pocket-ic binary, which exercises icp-cli's portability rather than this repo's.

Cost

macOS runners bill at 10×. Measured over the last 5 runs of each:

frontend_ic_vetkeys_mac        2.3 min  ->  23 billed min
cargo-test-backend-darwin      3.3 min  ->  33 billed min
backend-motoko-tests-darwin    3.4 min  ->  34 billed min
                               -------      ------------
                               9.0 min      ~90 billed min per full CI pass

Also cleaned up

clippy.yml and backend-rust-canbench.yml listed provision-darwin.sh in their paths: filters without ever running a macOS job. Those entries are removed along with the script.

Origin, for the record

The macOS jobs were never a considered decision. They trace to 803d2ca (Feb 2025), the first frontend CI commit, which had ubuntu-24.04 and macos-15 side by side from line one, and reached frontend.yml via #61 — a "merge crates and packages" refactor whose PR body is TODO description.

If we want some macOS coverage back

This is 98 lines of pure deletion, so git revert restores it exactly. A middle option, if the concern is that a month is a short window for a rare platform regression: re-add the jobs on push to main plus a nightly schedule instead of on pull_request. That keeps a signal for toolchain drift (provision-darwin.sh, Homebrew, the icp-cli/pocket-ic darwin binaries) at a fraction of the cost, since most runs are PR runs. Happy to do that instead if preferred.

🤖 Generated with Claude Code