feat(screenshare): integrate desktop audio exclusion

src/audio/echo_cancel.rs

@@ -33,12 +33,17 @@ const NODE_READY_TIMEOUT: Duration = Duration::from_secs(3);
 /// Owns a loaded `module-echo-cancel` instance; unloads it on drop so the virtual
 /// nodes never leak past the call that created them.
 pub struct EchoCancelGuard {
-    module_index: String,
+    module_index: u64,
     source_name: String,
     sink_name: String,
 }
 
 impl EchoCancelGuard {
+    /// The pactl module identity PixelPass validates in desktop-excluding mode.
+    pub fn module_index(&self) -> u64 {
+        self.module_index
+    }
+
     pub fn source_name(&self) -> &str {
         &self.source_name
     }
@@ -52,7 +57,7 @@ impl Drop for EchoCancelGuard {
     fn drop(&mut self) {
         let _ = Command::new("pactl")
             .arg("unload-module")
-            .arg(&self.module_index)
+            .arg(self.module_index.to_string())
             .output();
         crate::log_msg(&format!(
             "Echo cancel: unloaded module {}",
@@ -103,10 +108,10 @@ pub fn enable(
         ));
     }
 
-    let module_index = String::from_utf8_lossy(&out.stdout).trim().to_string();
-    if module_index.parse::<u64>().is_err() {
-        return Err(format!("unexpected pactl output: {module_index:?}"));
-    }
+    let raw_module_index = String::from_utf8_lossy(&out.stdout).trim().to_string();
+    let module_index = raw_module_index
+        .parse::<u64>()
+        .map_err(|_| format!("unexpected pactl output: {raw_module_index:?}"))?;
     let guard = EchoCancelGuard {
         module_index,
         source_name,