feat(host): recover desktop audio fanout after sink replacement

src/host/fanout.rs

@@ -133,6 +133,19 @@ pub(super) trait MutationProjectionSink: Send {
         now_us: u64,
         links: &mut dyn LinkMutation,
     );
+
+    /// Retarget a running controller to the exact serial of a recreated
+    /// connection-owned capture sink, then reconcile immediately against the
+    /// observer's current coherent projection. The adapter invokes this only
+    /// on its PipeWire loop thread, keeping old-link revocation and new-link
+    /// creation ordered with ordinary registry observations.
+    fn replace_capture_sink(
+        &mut self,
+        capture_sink: Serial,
+        projection: &Projection,
+        now_us: u64,
+        links: &mut dyn LinkMutation,
+    );
 }
 
 #[derive(Clone, Debug, PartialEq, Eq)]
@@ -339,6 +352,24 @@ impl MutationProjectionSink for FanoutController {
             self.emit_status(event);
         }
     }
+
+    fn replace_capture_sink(
+        &mut self,
+        capture_sink: Serial,
+        projection: &Projection,
+        now_us: u64,
+        links: &mut dyn LinkMutation,
+    ) {
+        if self.capture_sink == capture_sink {
+            return;
+        }
+        self.capture_sink = capture_sink;
+        // This is an explicit owner control message rather than a model event,
+        // so it must not be coalesced behind the next registry callback. The
+        // normal projection path is still the single place that evaluates,
+        // plans, revokes stale proxies, and determines all-links-ACTIVE.
+        self.on_projection(projection, EventKind::Graph, now_us, links);
+    }
 }
 
 /// Plan every candidate in the decision universe against one capture sink.
@@ -712,6 +743,36 @@ mod tests {
         );
     }
 
+    #[test]
+    fn replacing_the_capture_sink_drops_stale_links_and_recaptures() {
+        let (mut graph, app, old_sink, _) = stereo_graph();
+        let new_sink = graph.native_virtual_node("pixelpass_capture_new", MediaRole::Sink, 46);
+        let new_fl = graph.port_on_channel(new_sink, PortDirection::In, false, Some("FL"));
+        let new_fr = graph.port_on_channel(new_sink, PortDirection::In, false, Some("FR"));
+        let projection = projection(&graph);
+        let mut links = FakeLinks::default();
+        let mut controller = FanoutController::new(old_sink, AecConfig::Off);
+
+        controller.on_projection(&projection, EventKind::Graph, 1_000, &mut links);
+        assert_eq!(links.creates, 2);
+        assert_eq!(controller.states()[&app], StreamCaptureState::Captured);
+
+        controller.replace_capture_sink(new_sink.serial, &projection, 2_000, &mut links);
+
+        assert_eq!(links.drops, 2, "every old-sink proxy must be dropped");
+        assert_eq!(links.creates, 4, "both replacement links must be created");
+        assert_eq!(controller.states()[&app], StreamCaptureState::Captured);
+        assert_eq!(
+            links
+                .held
+                .iter()
+                .map(|link| link.input.port_id)
+                .collect::<BTreeSet<_>>(),
+            BTreeSet::from([new_fl, new_fr]),
+            "only replacement-sink ports may remain held"
+        );
+    }
+
     #[test]
     fn serial_revalidation_rejects_a_recycled_node_id_before_mutation() {
         let (mut graph, app, sink, _) = stereo_graph();