refactor(audio): extract pure parse_pw_nodes from device enumeration

Splits the pw-cli output parsing out of enumerate_audio_devices into a pure
fn parse_pw_nodes(&str) -> Vec<AudioDevice> (with a push_device helper),
leaving only the subprocess call in enumerate_audio_devices. Behavior-
preserving — same id-block boundaries, Audio/* filter, Source=>input,
description-falls-back-to-name, and sort-by-description. Creates a testable
seam (the parsing had zero coverage). Build + clippy clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/audio/pw_cli.rs

@@ -14,52 +14,59 @@ impl std::fmt::Display for AudioDevice {
 }
 
 pub fn enumerate_audio_devices() -> Vec<AudioDevice> {
-    let mut devices = Vec::new();
     let output = Command::new("pw-cli")
         .arg("list-objects")
         .arg("Node")
         .output();
-        
-    if let Ok(out) = output {
-        let text = String::from_utf8_lossy(&out.stdout);
-        let mut current_name = String::new();
-        let mut current_desc = String::new();
-        let mut current_class = String::new();
 
-        for line in text.lines() {
-            let line = line.trim();
-            if line.starts_with("id ") {
-                // Save previous if valid
-                if !current_name.is_empty() && current_class.starts_with("Audio/") {
-                    devices.push(AudioDevice {
-                        name: current_name.clone(),
-                        description: if current_desc.is_empty() { current_name.clone() } else { current_desc.clone() },
-                        is_input: current_class == "Audio/Source",
-                    });
-                }
-                current_name.clear();
-                current_desc.clear();
-                current_class.clear();
-            } else if let Some(val) = line.strip_prefix("node.name = \"") {
-                current_name = val.trim_end_matches('"').to_string();
-            } else if let Some(val) = line.strip_prefix("node.description = \"") {
-                current_desc = val.trim_end_matches('"').to_string();
-            } else if let Some(val) = line.strip_prefix("media.class = \"") {
-                current_class = val.trim_end_matches('"').to_string();
-            }
-        }
-        
-        // Final one
-        if !current_name.is_empty() && current_class.starts_with("Audio/") {
-            devices.push(AudioDevice {
-                name: current_name.clone(),
-                description: if current_desc.is_empty() { current_name } else { current_desc },
-                is_input: current_class == "Audio/Source",
-            });
+    match output {
+        Ok(out) => parse_pw_nodes(&String::from_utf8_lossy(&out.stdout)),
+        Err(_) => Vec::new(),
+    }
+}
+
+/// Emits the in-progress node as an `AudioDevice` if it's a complete Audio/*
+/// node, then resets the accumulators for the next block. Non-audio or
+/// incomplete blocks are dropped (but still reset).
+fn push_device(name: &mut String, desc: &mut String, class: &mut String, out: &mut Vec<AudioDevice>) {
+    if !name.is_empty() && class.starts_with("Audio/") {
+        out.push(AudioDevice {
+            name: name.clone(),
+            description: if desc.is_empty() { name.clone() } else { desc.clone() },
+            is_input: class == "Audio/Source",
+        });
+    }
+    name.clear();
+    desc.clear();
+    class.clear();
+}
+
+/// Parses the text of `pw-cli list-objects Node` into the audio devices we care
+/// about. Each object is a block introduced by an `id N, ...` line; within a
+/// block we collect `node.name` / `node.description` / `media.class`, and a
+/// device is emitted at the next `id` (and at EOF) when the class is `Audio/*`
+/// (`Audio/Source` => input). Description falls back to the node name when
+/// absent. Returned sorted by description for stable UI display.
+fn parse_pw_nodes(text: &str) -> Vec<AudioDevice> {
+    let mut devices = Vec::new();
+    let mut current_name = String::new();
+    let mut current_desc = String::new();
+    let mut current_class = String::new();
+
+    for line in text.lines() {
+        let line = line.trim();
+        if line.starts_with("id ") {
+            push_device(&mut current_name, &mut current_desc, &mut current_class, &mut devices);
+        } else if let Some(val) = line.strip_prefix("node.name = \"") {
+            current_name = val.trim_end_matches('"').to_string();
+        } else if let Some(val) = line.strip_prefix("node.description = \"") {
+            current_desc = val.trim_end_matches('"').to_string();
+        } else if let Some(val) = line.strip_prefix("media.class = \"") {
+            current_class = val.trim_end_matches('"').to_string();
         }
     }
-    
-    // Sort devices for consistent display
+    push_device(&mut current_name, &mut current_desc, &mut current_class, &mut devices);
+
     devices.sort_by(|a, b| a.description.cmp(&b.description));
     devices
 }