test(audio): unit tests for parse_pw_nodes device parser

Covers the pure pw-cli parser seam: multi-node parse sorted by description
(non-audio dropped), Source=>input / Sink=>output, description-falls-back-
to-name, empty/non-audio inputs yield nothing, EOF-flush of the final block,
and incomplete blocks (no media.class) dropped. pw_cli tests 0 -> 6.

Implemented by Gemini per next-task.md; left uncommitted per the operating-
agreement default, reviewed against the real diff and re-verified (build +
clippy --all-targets + test all green) by the senior.

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

src/audio/pw_cli.rs

@@ -70,3 +70,104 @@ fn parse_pw_nodes(text: &str) -> Vec<AudioDevice> {
     devices.sort_by(|a, b| a.description.cmp(&b.description));
     devices
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE_NODES: &str = r#"
+    id 33, type PipeWire:Interface:Node/3
+        node.name = "alsa_output.builtin"
+        node.description = "Built-in Speakers"
+        media.class = "Audio/Sink"
+    id 34, type PipeWire:Interface:Node/3
+        node.name = "alsa_input.builtin"
+        node.description = "Built-in Mic"
+        media.class = "Audio/Source"
+    id 35, type PipeWire:Interface:Node/3
+        node.name = "v4l2.cam"
+        media.class = "Video/Source"
+    id 36, type PipeWire:Interface:Node/3
+        node.name = "bare.sink"
+        media.class = "Audio/Sink"
+    "#;
+
+    #[test]
+    fn parses_audio_nodes_sorted_by_description() {
+        let devices = parse_pw_nodes(SAMPLE_NODES);
+
+        // exactly 3 devices (the Video/Source node is dropped)
+        assert_eq!(devices.len(), 3);
+
+        // order is by description: ["Built-in Mic", "Built-in Speakers", "bare.sink"]
+        // (uppercase "B" sorts before lowercase "b")
+        assert_eq!(devices[0].description, "Built-in Mic");
+        assert_eq!(devices[1].description, "Built-in Speakers");
+        assert_eq!(devices[2].description, "bare.sink");
+
+        // the mic device equals:
+        assert_eq!(
+            devices[0],
+            AudioDevice {
+                name: "alsa_input.builtin".into(),
+                description: "Built-in Mic".into(),
+                is_input: true,
+            }
+        );
+    }
+
+    #[test]
+    fn source_is_input_sink_is_output() {
+        let devices = parse_pw_nodes(SAMPLE_NODES);
+        // Find devices by name or description to verify is_input
+        let mic = devices.iter().find(|d| d.name == "alsa_input.builtin").unwrap();
+        let speakers = devices.iter().find(|d| d.name == "alsa_output.builtin").unwrap();
+        let bare = devices.iter().find(|d| d.name == "bare.sink").unwrap();
+
+        assert!(mic.is_input);
+        assert!(!speakers.is_input);
+        assert!(!bare.is_input);
+    }
+
+    #[test]
+    fn description_falls_back_to_node_name() {
+        let devices = parse_pw_nodes(SAMPLE_NODES);
+        let bare = devices.iter().find(|d| d.name == "bare.sink").unwrap();
+        assert_eq!(bare.description, "bare.sink");
+    }
+
+    #[test]
+    fn non_audio_and_empty_inputs_yield_nothing() {
+        assert!(parse_pw_nodes("").is_empty());
+
+        let video_sample = r#"
+        id 35, type PipeWire:Interface:Node/3
+            node.name = "v4l2.cam"
+            media.class = "Video/Source"
+        "#;
+        assert!(parse_pw_nodes(video_sample).is_empty());
+    }
+
+    #[test]
+    fn final_block_is_emitted_at_eof() {
+        let single_sample = r#"
+        id 99, type PipeWire:Interface:Node/3
+            node.name = "single.device"
+            media.class = "Audio/Sink"
+        "#;
+        let devices = parse_pw_nodes(single_sample);
+        assert_eq!(devices.len(), 1);
+        assert_eq!(devices[0].name, "single.device");
+    }
+
+    #[test]
+    fn incomplete_block_without_class_is_dropped() {
+        let incomplete_sample = r#"
+        id 100, type PipeWire:Interface:Node/3
+            node.name = "incomplete.device"
+            node.description = "Incomplete Device"
+        "#;
+        let devices = parse_pw_nodes(incomplete_sample);
+        assert!(devices.is_empty());
+    }
+}