Synchronous AccessibleObjectFromEvent and IAccessible property queries on
the helper's WinEvent thread could block native typing and focus feedback
while an application-owned accessibility provider stopped responding.
Move those calls into MsaaEventReader, a single COM worker that owns its
native references and exchanges copied requests and results with the event
thread. Bound both queues to 32 entries, invalidate queued work on focus or
foreground changes, and discard results older than 500 ms. Validate the
window, process, thread, generation, and foreground relationship before
presenting a result. Read protected state before querying accessible values.
Reject unrelated background presentation events before invoking providers
or invalidating foreground work. Preserve accessible events from visible
popups owned by the foreground window. Keep existing native menu, editor,
combo, list, and item-control paths, and use native focus fallback when an
MSAA focus request expires or fails.
Poll completed results from the existing event timer. On shutdown, retire
pending work and wait at most 100 ms for the worker; a blocked COM call keeps
only its own state until it completes or the helper process exits. Never
spawn additional workers behind an unresponsive provider.
Validation: CMake configure/build and git diff --check passed. On a private
dummy Xorg display, all four CTest checks passed, as did six event-stall
runs (default, --32-bit, --getter, --background, --popup, --reader orca)
and the existing menu, edit, controls, and list fixtures in both 64-bit and
32-bit modes. See the accompanying regression-test commit for commands.
Private recording-service fixtures do not establish audible speech, physical braille,
or acceptance of every live MUSHclient workflow. A provider that never
returns occupies the single MSAA worker until helper exit.
