callstack__agent-device/docs/adr/0009-apple-platform-consolidation.md

ADR 0009: Apple Platform Consolidation (AppleOS leaf axis)

Status

Accepted

Context

Apple support is modeled asymmetrically and is physically smeared across an ios directory that is really the shared Apple engine. Platform carries ios and macos as separate literals, but tvOS is not a platform at all — it is platform: 'ios' + target: 'tv', with the OS name reconstructed late and lossily by resolveApplePlatformName (src/kernel/device.ts). Meanwhile ~697 LOC of macOS code lives inside src/platforms/ios/, src/platforms/macos/devices.ts is a 19-line stub that the iOS discovery imports (the dependency arrow points backwards), and the Apple interactor in src/core/interactors/apple.ts reaches into platforms/ios. A four-investigator survey found that ~85% of platforms/ios (the runner stack, tool-provider, discovery, snapshot, screenshot, perf, debug-symbols) is already OS-agnostic, and the XCTest runner already builds ios | macos | tvos from one Xcode project. Distinguishing or adding an Apple OS today is therefore costly out of proportion to the actual work, and iPadOS/visionOS/watchOS are unmodeled.

Decision

Model Apple OSes with an AppleOS discriminant (ios | ipados | tvos | watchos | visionos | macos) under a single apple Platform — not six Platform literals. The OS-agnostic Apple engine consolidates under src/platforms/apple/core/, with genuinely per-OS code in src/platforms/apple/os/<os>/ leaves; the Apple plugin is the first instance of the platform-plugin registry (the platform axis of the completed perfect-shape refactor; see CONTEXT.md Architecture). Per-OS capability differences become data keyed by AppleOS. The additive, non-breaking appleOs discriminant — the groundwork for this — shipped in #896.

Alternatives Considered

• Promote each Apple OS to its own Platform literal: rejected. DeviceTarget (mobile | tv | desktop) is already cross-platform (Android TV uses target: 'tv'), so a tvos literal collides with the form-factor axis; it would also force the ~15 isApplePlatform and ~52 macos branch sites to enumerate six literals and break the single-bucket apple capability/selector model that already works.
• Keep the status quo: rejected — the tvOS/macOS asymmetry, the mislabeled macOS code, and the lossy target→OS inference persist, with no path to iPadOS/visionOS.
• Exclude macOS from the consolidation: rejected. macOS is already entangled — it builds via the same XCUITest project and ~697 LOC of its code already lives inside platforms/ios. Excluding it would leave the mislabel in place; including it as a distinct AppKit leaf normalizes it without homogenizing it.

Consequences

Adding a first-class Apple OS becomes cheap: a leaf module plus a runner-profile row. iOS/iPadOS/tvOS/macOS are mostly relocate-and-rename (the engine never needed to know which Apple OS it drives); visionOS is scoped net-new work (XCUITest supports it — a profile row, a build case, #if os(visionOS), a widened discovery filter, plus real spatial-input QA); watchOS is an explicit unsupported sentinel because XCUITest cannot drive watchOS UI. macOS stays a distinct AppKit leaf (its helper binary and menubar/desktop surface model are preserved). The tvOS focus-only interaction contract (no coordinate tap) must not be flattened across OSes, and snapshot fidelity is uneven (the deep-RN AX-server fallback is iOS-simulator-only). The final Platform collapse of ios+macos into apple is the last, highest-diff step.

This composes with ADR 0008 (the descriptor's capability facet) and ADR 0003.

Implementation status as of 2026-07:

• Shipped: additive appleOs groundwork; the shared Apple engine under src/platforms/apple/core; macOS leaf files under src/platforms/apple/os/macos; a dedicated tvOS leaf under src/platforms/apple/os/tvos; direct internal imports to the Apple modules; the per-AppleOS capability table (APPLE_OS_CAPABILITIES, src/platforms/apple/capabilities.ts, parity-pinned against the pre-table predicates); the watchOS unsupported sentinel (reserved in the AppleOS type and interactor-rejected — XCUITest cannot drive watchOS UI — never produced by discovery); and visionOS profile/build/discovery groundwork.
• Deferred: the public Platform collapse from ios/macos to apple (the last, highest-diff step; the public wire still emits ios/macos leaves via PUBLIC_PLATFORMS) and net-new visionOS spatial-input QA.

This ADR owns the architectural decision. The Phase 3 platform-plugin umbrella (#972) is closed; within this consolidation the public Platform collapse above is the last deferred step (net-new visionOS spatial-input QA is separate follow-up, outside the consolidation).