feat(setup): add arm64 support and runner.arch input

[alexFilichkin]

Problem

setup/setup_snyk.sh branches only on runner.os and unconditionally downloads the amd64 binary (e.g. snyk-linux). On arm64 runners — increasingly common with AWS CodeBuild, Apple Silicon self-hosted runners, and the GA ubuntu-24.04-arm images — the binary cannot exec:

/usr/local/bin/snyk: line 5: /usr/local/bin/snyk-linux: cannot execute binary file: Exec format error
Installed Snyk v        # empty version

Subsequent snyk invocations exit with code 126 (command found but not executable) in ~9 ms, masking the real failure. This was first hit in a real downstream workflow on a CodeBuild ARM64 runner.

Snyk already publishes arm64 binaries at the same CDN — snyk-linux-arm64, snyk-macos-arm64, snyk-alpine-arm64 (all return HTTP 200 from https://downloads.snyk.io/cli/latest/) — they're just never selected.

Change

1. setup/setup_snyk.sh — accepts an optional 3rd positional arg for CPU architecture. When omitted, falls back to uname -m, so existing 2-arg callers keep working. New case statement maps:

   • X64 / x86_64 / amd64 → "" (default binary, unchanged behavior)
   • ARM64 / aarch64 / arm64 → -arm64
   • anything else → die with a clear message
   • arm64 is only accepted for platforms where Snyk publishes a binary (linux, macos, alpine).
   • Introduces BINARY="snyk-${PREFIX}${ARCH_SUFFIX}" so download/checksum/move all stay consistent.

2. setup/action.yml — new optional arch input defaulting to ${{ runner.arch }}, plumbed through as the third arg.

Backwards compatibility

Runner OS	Runner Arch	Resolves to	vs. today
Linux	X64 / x86_64	snyk-linux	unchanged
Linux	ARM64 / aarch64	snyk-linux-arm64	fix
macOS	X64	snyk-macos	unchanged
macOS	ARM64	snyk-macos-arm64	fix
Alpine	X64	snyk-alpine	unchanged
Alpine	ARM64	snyk-alpine-arm64	fix
Windows	*	die (existing behavior)	unchanged

Existing callers that pass only 2 args (version, OS) keep working because the script falls back to uname -m for the arch. The action's arch input defaults to runner.arch, so existing workflows that only set os (or accept the default) are unaffected.

Test plan

• Smoke-tested all 8 OS×arch combinations through the case logic locally.
• Verified the three new arm64 URLs (snyk-linux-arm64, snyk-macos-arm64, snyk-alpine-arm64) all return HTTP 200 from downloads.snyk.io/cli/latest/.
• bash -n setup_snyk.sh passes.
• CI on this PR.

[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Code Security	0	0	0	0	0 issues

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