Add supported_platforms to cask API data

[p-linnane]

Cask variations became explicit for every valid OS and architecture tag in 233377e. formulae.brew.sh read the presence of Linux variations as evidence of Linux support, so macOS-only casks such as VSCodium advertised Linux. variations describes per-platform data overrides and has to keep entries for unsupported platforms, so support cannot be inferred from it.

This adds a top-level supported_platforms array listing every tag a cask can install on, emitted for every cask. It applies the rules the installer already enforces, including the artifact type rules that previously only existed in the extend/os prepends and so were invisible to API generation.

The audit rule requiring an installable artifact has been a no-op since cask.artifacts became a set of artifact objects rather than a symbol-keyed hash. It now checks properly, across valid tags. One cask in homebrew/cask was affected, fixed in Homebrew/homebrew-cask#280460; third-party casks with only uninstall and zap will start failing audit.

Adds roughly 1.68 MB raw to cask.jws.json, 9.8 KB gzipped.

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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

Claude Code (Opus 5) drafted the implementation and tests; I reviewed the diff, verified the new tests fail without the fix and pass with it, and ran brew lgtm + targeted specs.

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[Copilot]

Pull request overview

Adds an explicit supported_platforms field to Cask API serialization so downstream consumers can determine installability per OS/arch without inferring support from variations, and centralises platform artifact support rules into the core Cask model.

Changes:

• Emit a top-level supported_platforms array from Cask::Cask#to_hash_with_variations, applying installer/audit-equivalent eligibility rules per valid OS/arch tag.
• Move OS-specific “artifact supported on this OS” logic into Cask::Cask#artifacts_supported_on_os? and reuse it from macOS/Linux installer checks.
• Fix the required-stanzas audit to properly require an installable artifact (including across on_system-scoped casks) and add coverage for uninstall-only and Linux-only-installable cases.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Library/Homebrew/cask/cask.rb	Adds installable_artifact?, artifacts_supported_on_os?, and supported_platforms emission with per-tag support filtering.
Library/Homebrew/cask/audit.rb	Updates required-stanzas audit to validate presence of an installable artifact (including across tags for on_system casks).
Library/Homebrew/cask/installer.rb	Reuses installable_artifact? when rejecting API-loaded casks that lack installable artifacts on the current system.
Library/Homebrew/extend/os/mac/cask/installer.rb	Switches stanza OS requirement checks to use cask.artifacts_supported_on_os?(:macos).
Library/Homebrew/extend/os/linux/cask/installer.rb	Switches stanza OS requirement checks to use cask.artifacts_supported_on_os?(:linux).
Library/Homebrew/test/cask/cask_spec.rb	Adds unit coverage for artifacts_supported_on_os? and supported_platforms behaviour across OS/arch/tag scenarios.
Library/Homebrew/test/cask/audit_spec.rb	Adds audit coverage for uninstall-only casks and casks installable only on Linux via on_linux.

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[MikeMcQuaid]

Thanks!