Stop inferring cask OS support from artifact types

[p-linnane]

Cask operating system support is now determined solely by explicit depends_on declarations. Artifact types no longer imply a platform, so app no longer means macOS-only and app_image no longer means Linux-only. This follows up on review feedback in #23503, where the artifact tables acted as a second source of platform truth alongside depends_on.

Cask::Artifact::MACOS_ONLY_ARTIFACTS, LINUX_ONLY_ARTIFACTS and Cask#artifacts_supported_on_os? are gone, and the installer checks use supports_linux? and supports_macos? directly. The macOS prepend became identical to the shared implementation, so it is deleted. supported_platforms still filters on download completeness, installable artifact presence, architecture and macOS version, so casks that scope their artifacts with on_macos or on_linux are unaffected.

Homebrew/OSDependsOn is now solely responsible for requiring OS dependencies on OS-specific artifact stanzas, so it also detects artifacts inside on_arm, on_intel and on_system, which all run on both operating systems, and places autocorrected stanzas in the right group. Where a cask shows cross-platform intent, through a sibling on_macos or on_linux block, an on_system block, or artifacts for both operating systems, it reports the stanza without autocorrecting, since a bare dependency there would drop platform support or produce contradictory stanzas. Checked against all 7,695 casks in homebrew/homebrew-cask with no new offenses.

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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 change and pass with it, and ran brew lgtm --online plus targeted specs.

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[MikeMcQuaid]

Nice thanks!

[Copilot]

Pull request overview

This PR removes artifact-type-based inference of Cask OS support and makes OS support determination rely solely on explicit depends_on declarations, aligning installer behavior and API serialization with a single source of truth.

Changes:

• Removes Cask::Cask#artifacts_supported_on_os? and the Cask::Artifact::*_ONLY_ARTIFACTS constants, and stops filtering supported_platforms based on artifact types.
• Updates installer OS checks to use supports_macos?/supports_linux? directly and drops the now-redundant macOS installer prepend.
• Expands Homebrew/OSDependsOn RuboCop cop coverage to detect OS-specific artifacts inside on_arm/on_intel/on_system blocks and adds/updates specs accordingly.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Library/Homebrew/test/rubocops/os_depends_on_spec.rb	Adds coverage for OSDependsOn behavior with architecture and on_system blocks, including non-autocorrect cases for cross-platform intent.
Library/Homebrew/test/cask/cask_spec.rb	Updates supported platform expectations to ensure OS support is not inferred from artifact types, and adds explicit depends_on OS-only cases.
Library/Homebrew/rubocops/os_depends_on.rb	Refactors OSDependsOn to handle platform blocks and cross-platform intent detection while preserving autocorrect insertion ordering.
Library/Homebrew/extend/os/mac/cask/installer.rb	Removes macOS-specific installer prepend now that shared behavior is sufficient.
Library/Homebrew/extend/os/linux/cask/installer.rb	Simplifies Linux installer OS requirement check to rely on supports_linux?.
Library/Homebrew/extend/os/cask/installer.rb	Drops conditional require of the deleted macOS installer extension.
Library/Homebrew/cask/cask.rb	Removes artifact-based OS filtering and the artifacts_supported_on_os? method.
Library/Homebrew/cask/artifact/abstract_artifact.rb	Moves/keeps the module-level documentation for Cask::Artifact.
Library/Homebrew/cask/artifact.rb	Removes OS-only artifact constant tables that were previously used for inference.
docs/Cask-Cookbook.md	Updates documentation to describe OS support determination via depends_on (needs clarification per review comment).

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