WindowAdmissionResolver — Specs

Product object

AltTab offers switch destinations, not every rectangle WindowServer paints. PhysicalSurface owns existence, geometry, level and parentage. SemanticSurface owns AX meaning. SwitchDestinationDecision joins them without giving either source universal authority.

Rules

1. WID zero is invalid.
2. A WindowServer parent is an exact relationship: represent the parent, regardless of level, size or attention.
3. Placement gates every surface, on every channel. A destination sits at the ordinary window level or covers the screen, unless AX positively marks it kAXMain. Above that level an app puts its HUDs, panels and overlays, and no subrole distinguishes them: Chromium describes ChatGPT's dictation strip as a titled AXDialog and its sidebar as AXStandardWindow, the same subroles every ordinary AppKit window carries. The gate binds exact attention too, because an app key-focuses its own HUD through kAXFocusedWindow exactly as a real window does, so gating only discovery would delay the surface by one focus event.
4. Exact attention makes a parentless, admissibly-placed surface a destination even when AX is absent or unconventional, but it cannot override an auxiliary subrole or a role that is not a window.
5. Floating/system-dialog subroles are auxiliary. AppKit can mark a floating panel kAXMain; that does not turn the panel into a switch destination.
6. A non-auxiliary AXWindow marked kAXMain is a destination.
7. AXStandardWindow is a destination. A titled AXDialog is a destination; an untitled one remains latent.
8. A substantial, titled AXWindow root is a custom-toolkit destination. This generic rule replaces app-name exceptions for Steam, Wine, presentation windows and similar unconventional apps.
9. Size is an acquisition prior, never a rejection gate: level-zero surfaces are inspected even when small, substantial surfaces are inspected at every level, and exact attention bypasses the optimization.
10. A result is recomputed whenever semantic evidence is refreshed. No acceptance or rejection is permanent.

Boundaries

100×50 is substantial. Native AppKit tabs are logical destinations handled by TabGroupResolver; WindowServer parentage intentionally says nothing about them because both active and background native tabs report parent zero.

Application boundary

Window admission and application admission use the same evidence without conflating their permissions. Ordinary discovery still excludes XPC processes unless they are an established user-facing exception. Exact attention may admit the process which owns that destination; zombie status always rejects it. Owning an exact destination does not grant speculative placeholders: only regular apps get one. An accessory or prohibited process that briefly took focus (Raycast's palette, CoreServicesUIAgent's Gatekeeper alert) is not an app the user can switch back to.