Android enables Flutter semantics for any bound accessibility service, so a
TV running the Projectivy Launcher (whose service only wants foreground-app
events) paid for a full semantics tree on every frame that touched a node:
on an Android 14 box, 2 ms per frame, ~20 ms on each spotlight swap, and a
third of the navigation-time GC churn.
The Android side now reports whether any enabled service can consume the
tree (touch exploration, an accessibility tool, or spoken/braille/audible/
visual feedback; an empty list means UiAutomation, which reads it too), and
AssistiveTechnologyService closes a SemanticsTreeGate on the app binding
when none can. The gate sits under SemanticsBinding.semanticsEnabled, so the
pipeline owner drops the semantics owner exactly as if the platform had
turned accessibility off; explicit ensureSemantics clients (the debug handle
for Maestro) always win. Re-evaluated on platform toggles, service-list
changes (API 33+) and resume.
Cold navigation on the box with Projectivy's service bound, 30 D-pad steps
over three hubs: SEMANTICS phase 700-770 ms -> 0, UI frame max 31-37 ms ->
25 ms, GC 3.0 s -> 2.2-2.6 s.
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