fix(host/audio): a VoiceMeeter box can no longer loop the mic into the stream

wiring_plan could hand the mic Voicemeeter Input and the loopback
Voicemeeter Aux Input — two strips of the same internal mixer, i.e. a
digital feedback loop with no acoustic path to break it, because
leftover() never asked virtualish() and the exclusion list only knew
"cable" and the Steam Speakers. Now every VoiceMeeter or generically
"virtual" render is excluded from loopback, and the last-resort tier
refuses anything virtual: a box with only mixer endpoints gets
loopback=None, honest like the cable-only case.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/punktfunk-host/src/audio/wiring_plan.rs

@@ -69,11 +69,18 @@ fn capture_for(mic_render_lname: &str) -> &'static [&'static str] {
 }
 
 /// A render endpoint no loopback should capture: the VB-CABLE (reserved for the mic even when it
-/// isn't the chosen target — capturing a cable someone else feeds echoes too) and the Steam
-/// Streaming Speakers, whose loopback is silent (validated live). Also the capture-side
-/// watchdog's test for "the operator's new default can never work — snap back to the plan".
+/// isn't the chosen target — capturing a cable someone else feeds echoes too), the Steam
+/// Streaming Speakers, whose loopback is silent (validated live), and any VoiceMeeter or
+/// generically-"virtual" endpoint. VoiceMeeter's strips share one internal mixer: capturing ANY
+/// of its render endpoints re-captures what the mic wrote into another one — a digital feedback
+/// loop with no acoustic path to break it (mic=`Voicemeeter Input`, loopback=`Voicemeeter Aux
+/// Input` used to pass the old name checks). Also the capture-side watchdog's test for "the
+/// operator's new default can never work — snap back to the plan".
 pub(crate) fn excluded_from_loopback(lname: &str) -> bool {
-    lname.contains("cable") || lname.contains("steam streaming speakers")
+    lname.contains("cable")
+        || lname.contains("steam streaming speakers")
+        || lname.contains("voicemeeter")
+        || lname.contains("virtual")
 }
 
 /// A render endpoint that is SILENT on the host but loopback-capturable — the client-only audio
@@ -140,10 +147,14 @@ pub(crate) fn plan(
             .iter()
             .find(|(n, id)| not_mic(id) && silent_sink(&n.to_lowercase()))
     };
+    // `virtualish` here too: a virtual endpoint that slipped past `excluded_from_loopback`'s
+    // name list (a future cable/mixer sibling) is an internal-feedback loop waiting to happen —
+    // no loopback is the honest answer, exactly like the cable-only case.
     let leftover = || {
-        renders
-            .iter()
-            .find(|(n, id)| not_mic(id) && !excluded_from_loopback(&n.to_lowercase()))
+        renders.iter().find(|(n, id)| {
+            let ln = n.to_lowercase();
+            not_mic(id) && !excluded_from_loopback(&ln) && !virtualish(&ln)
+        })
     };
     let loopback_render = if host_audio {
         real_hw().or_else(silent).or_else(leftover)
@@ -359,4 +370,59 @@ mod tests {
         assert!(w.mic_render.is_none());
         assert_eq!(w.loopback_render.unwrap().0, "Speakers (Realtek HD Audio)");
     }
+
+    /// VoiceMeeter box with real hardware: no cable, so the mic takes `Voicemeeter Input` — and
+    /// the loopback must NEVER be `Voicemeeter Aux Input` (same internal mixer: capturing any
+    /// VoiceMeeter render re-captures what the mic wrote — a digital feedback loop). Real
+    /// hardware wins the loopback in both modes.
+    #[test]
+    fn voicemeeter_aux_never_pairs_with_voicemeeter_mic() {
+        let renders = [
+            ep("Voicemeeter Input (VB-Audio Voicemeeter VAIO)"),
+            ep("Voicemeeter Aux Input (VB-Audio Voicemeeter AUX VAIO)"),
+            ep("Speakers (Realtek HD Audio)"),
+        ];
+        let captures = [ep("Voicemeeter Out B1 (VB-Audio Voicemeeter VAIO)")];
+        for host_audio in [false, true] {
+            let w = plan(&renders, &captures, None, host_audio);
+            assert_eq!(
+                w.mic_render.as_ref().unwrap().0,
+                "Voicemeeter Input (VB-Audio Voicemeeter VAIO)",
+                "host_audio={host_audio}"
+            );
+            assert_eq!(
+                w.loopback_render.as_ref().unwrap().0,
+                "Speakers (Realtek HD Audio)",
+                "host_audio={host_audio}"
+            );
+        }
+    }
+
+    /// Only VoiceMeeter endpoints (headless mixer box): mic wins one, the loopback is honestly
+    /// absent — like the cable-only case, never another strip of the same mixer.
+    #[test]
+    fn voicemeeter_only_no_loopback() {
+        let renders = [
+            ep("Voicemeeter Input (VB-Audio Voicemeeter VAIO)"),
+            ep("Voicemeeter Aux Input (VB-Audio Voicemeeter AUX VAIO)"),
+        ];
+        for host_audio in [false, true] {
+            let w = plan(&renders, &[], None, host_audio);
+            assert!(w.mic_render.is_some(), "host_audio={host_audio}");
+            assert!(w.loopback_render.is_none(), "host_audio={host_audio}");
+        }
+    }
+
+    /// A generically-"virtual" leftover (unknown vendor cable) is refused too: `leftover()`
+    /// applies `virtualish`, so a virtual endpoint that slips past the name list can't become
+    /// the loopback.
+    #[test]
+    fn unknown_virtual_never_loopback() {
+        let renders = [
+            ep("CABLE Input (VB-Audio Virtual Cable)"),
+            ep("Speakers (Some Virtual Audio Device)"),
+        ];
+        let w = plan(&renders, &[], None, false);
+        assert!(w.loopback_render.is_none());
+    }
 }