fix(audio_backend): never throw across the PulseAudio callback boundary

connectContext() throws std::runtime_error when pa_context_connect() fails.
It was called directly from contextStateCb (the libpulse mainloop thread,
running pure-C callback frames) on the PA_CONTEXT_FAILED reconnect path, so on
a pipewire/pulse restart the exception unwound across the C callback boundary
and triggered std::terminate/SIGABRT.

Add reconnectContext() noexcept which wraps connectContext() and logs failures
instead of throwing, and use it from the callback. Guard against the
FAILED -> connect -> FAILED recursion/busy loop with a reentrancy flag. The
constructor-time connectContext() still throws as before.

Fixes #5141.

include/util/audio_backend.hpp

@@ -29,10 +29,17 @@ class AudioBackend {
   static void volumeModifyCb(pa_context*, int, void*);
   static void sourceVolumeModifyCb(pa_context*, int, void*);
   void connectContext();
+  // Non-throwing reconnect used from the PulseAudio callback thread. Throwing
+  // across the libpulse C callback boundary calls std::terminate, so this
+  // swallows any failure and reports it via the return value instead.
+  bool reconnectContext() noexcept;
 
   pa_threaded_mainloop* mainloop_;
   pa_mainloop_api* mainloop_api_;
   pa_context* context_;
+  // Guards against the FAILED -> connect -> FAILED recursion / busy loop when a
+  // reconnect attempt fails synchronously inside pa_context_connect().
+  bool reconnecting_{false};
   pa_cvolume pa_volume_;
   pa_cvolume pa_source_volume_;