Fix test setup crash when multiple package APIs are cached

[p-linnane]

The per-example RSpec setup links the real API cache into the sandbox cache. Library/Homebrew/test/spec_helper.rb treated every packages.*.jws.json in the source cache as a fan-out source, so when the real cache held more than one tag (for example packages.arm64_golden_gate.jws.json and packages.arm64_tahoe.jws.json) the first source created the alias for the second source's target, and linking the second source then raised Errno::EEXIST during setup and broke brew tests.

Setup now picks a single package source, preferring the running tag (Homebrew::SimulateSystem.current_tag) and falling back to the first available, skips packages.* files in the generic copy/link loop, and fans out the per-tag aliases once from that one source. Non-package cache files keep the existing copy/link behavior, now guarded by an existence check so a repeated setup pass is idempotent.

Holding package APIs for multiple tags is a legitimate cache state that any --os/--arch run or OS upgrade can produce, so this is test-helper resilience rather than a brew cleanup change.

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• AI was used to generate or assist with generating this PR.

Claude Code (Opus 4.8) diagnosed the setup crash and produced the fix; I reviewed the diff and verified with brew lgtm plus targeted dev-cmd/tests and rubocop specs.

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[Copilot]

Pull request overview

This pull request hardens the RSpec per-example sandbox setup in spec_helper.rb to avoid crashes when the real Homebrew API cache contains multiple per-tag package API files (a legitimate state after --os/--arch usage or OS upgrades). It makes API cache setup resilient by selecting a single package API source to fan out into the sandbox and by making the copy/link steps idempotent.

Changes:

• Introduces a single selected packages.*.jws.json source (prefer current running tag; otherwise first available) and fans out tag aliases from that one file to prevent collisions.
• Excludes packages.* from the generic api/internal copy/link loop to avoid Errno::EEXIST when multiple package files exist.
• Adds target.exist? guards to make cache setup safe across repeated setup passes (e.g., retries) without raising.

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[MikeMcQuaid]

Thanks!