fix(pad-audio): the Linux pad sink speaks GE-Proton's AUX0-3 channel shape

A field report (GE-Proton 11-5, real DualSense on-host) surfaced the missing
constraint: haptics only work when the pad's card runs the Pro Audio profile —
because GE's route opens the node through its bundled pipewire-alsa plugin
with aux_channels=1, and its pulse fallback forces a PA AUX0..3 map with
stream.dont-remix (proton-ds5-haptic patches 0013/0115/0116: "the hidden
PipeWire parent for a DualSense output exposes AUX0 through AUX3"). A
positioned FL FR RL RR sink puts those writers through position channelmix
instead of index passthrough.

The sink now advertises AUX0..AUX3. Proven on the box: an AUX-mapped
rear-pair-only tone captures index-exact (speaker pair 0.0000, coil pair
0.3662); a positioned stray stream folds into the speaker pair and never
excites the coils. The devtest reports per-pair peaks so exactly this class
of remix bug is visible.

Also confirmed from the GE patch set while here: device matching is
device.bus/vendor.id/product.id + the Sony/Wireless_Controller name
substrings (both of which the sink carries), and the MMDevice container is
now synthesized from the wine-side HID USB parent (patch 0112) — the old
pure-PW-node GUID_NULL concern no longer applies on GE >= 11-4.

crates/punktfunk-host/src/audio/linux/pad_sink.rs

@@ -198,12 +198,21 @@ impl crate::audio::AudioCapturer for PadSinkCapturer {
     }
 }
 
-/// SPA channel positions for the pad quad: FL FR RL RR (`enum spa_audio_channel`: FL=3 FR=4
-/// RL=12 RR=13). NOT the session capturer's 4-ch order — the pad layout has no center/LFE; the
-/// rear pair is the voice coils.
+/// SPA channel positions for the pad quad: AUX0..AUX3 (`enum spa_audio_channel`:
+/// `SPA_AUDIO_CHANNEL_START_Aux` = 0x1000), NOT a positioned FL FR RL RR layout. This is the
+/// shape a REAL DualSense exposes on the PipeWire path GE-Proton's haptics were built and
+/// field-validated against: its `open_dualsense_haptic_pcm` targets the node through the
+/// bundled pipewire-alsa plugin with `aux_channels=1` — "the hidden PipeWire parent for a
+/// DualSense output exposes AUX0 through AUX3" (proton-ds5-haptic patch 0115) — and its pulse
+/// fallback forces a `PA_CHANNEL_POSITION_AUX0..3` map. On a real pad that shape is the card's
+/// Pro Audio profile (the community-reported requirement for GE ≥11-4). Aux positions carry no
+/// spatial meaning, so nothing in the graph position-remixes into (or out of) the sink —
+/// writers land by INDEX, exactly the raw quad the pad speaks: ch0/1 = speaker, ch2/3 = voice
+/// coils (the same order the Windows endpoint is stamped with and `split_quad` assumes).
 fn pad_positions() -> [u32; 64] {
+    const AUX0: u32 = 0x1000;
     let mut pos = [0u32; 64];
-    pos[..4].copy_from_slice(&[3, 4, 12, 13]);
+    pos[..4].copy_from_slice(&[AUX0, AUX0 + 1, AUX0 + 2, AUX0 + 3]);
     pos
 }
 

crates/punktfunk-host/src/devtest.rs

@@ -261,22 +261,30 @@ pub fn pad_sink_test(args: &[String]) -> Result<()> {
         cap.node_name, cap.node_name
     );
     let deadline = Instant::now() + Duration::from_secs(secs);
-    let (mut chunks, mut samples, mut peak) = (0u64, 0u64, 0f32);
+    let (mut chunks, mut samples) = (0u64, 0u64);
+    // Per-pair peaks: ch0/1 = speaker, ch2/3 = voice coils — the split_quad contract. Proving
+    // the pairs separately is the point of this devtest: a positional remix upstream would
+    // smear or zero one pair while a global peak still looks healthy.
+    let (mut peak_spk, mut peak_coil) = (0f32, 0f32);
     let mut last_report = Instant::now();
     while Instant::now() < deadline {
         let c = cap.next_chunk().context("pad sink capture")?;
         if !c.is_empty() {
             chunks += 1;
             samples += c.len() as u64;
-            peak = c.iter().fold(peak, |p, s| p.max(s.abs()));
+            for f in c.chunks_exact(4) {
+                peak_spk = peak_spk.max(f[0].abs()).max(f[1].abs());
+                peak_coil = peak_coil.max(f[2].abs()).max(f[3].abs());
+            }
         }
         if last_report.elapsed() >= Duration::from_secs(1) {
             last_report = Instant::now();
             println!(
-                "  chunks={chunks} samples={samples} (~{:.1}ms of 4ch audio) peak={peak:.4}",
+                "  chunks={chunks} samples={samples} (~{:.1}ms of 4ch audio) \
+                 peak_speaker={peak_spk:.4} peak_coils={peak_coil:.4}",
                 samples as f64 / (4.0 * 48.0)
             );
-            (chunks, samples, peak) = (0, 0, 0.0);
+            (chunks, samples, peak_spk, peak_coil) = (0, 0, 0.0, 0.0);
         }
     }
     println!("pad-sink-test: done");