fix: name the audio device in diagnostics instead of quoting its GUID

The watchdog fired exactly as intended and said:

  no audio at all from "{0.0.1.00000000}.{6a27abfd-f277-496b-b6f1-f92ec284c636}"

which tells the operator nothing they can act on. "DAX RX 1 (FlexRadio DAX)"
points straight at the DAX panel.

Endpoint ids are what gets CONFIGURED and stored, so they are what the recorder
holds; the friendly name is resolved only when something has gone wrong. When
the endpoint cannot be found at all the id is still shown — a device that has
disappeared explains an empty recording too.

internal/audio/devices.go

@@ -101,3 +101,30 @@ func endpointName(dev *wca.IMMDevice, fallback string) string {
 	}
 	return fallback
 }
+
+// DeviceName resolves an endpoint id to its friendly name.
+//
+// Diagnostics quote the id that was CONFIGURED, which is a GUID — an operator
+// told "no audio at all from {0.0.1.00000000}.{6a27abfd…}" learns nothing they
+// can act on, while "no audio at all from DAX RX 1 (FlexRadio DAX)" points
+// straight at the DAX panel.
+//
+// Falls back to the id when the endpoint cannot be found, which is itself worth
+// seeing: a device that has disappeared explains an empty recording too.
+func DeviceName(id string) string {
+	if id == "" {
+		return "(none)"
+	}
+	for _, list := range []func() ([]Device, error){ListInputDevices, ListOutputDevices} {
+		devs, err := list()
+		if err != nil {
+			continue
+		}
+		for _, d := range devs {
+			if d.ID == id {
+				return d.Name
+			}
+		}
+	}
+	return id
+}

internal/audio/recorder.go

@@ -155,7 +155,7 @@ func (r *Recorder) Start(fromDev, micDev string, prerollSec int) error {
 			r.lastA = time.Now()
 			r.srcMu.Unlock()
 		}); err != nil {
-			LogSink("recorder: capture from %q failed: %v", fromDev, err)
+			LogSink("recorder: capture from %q failed: %v", DeviceName(fromDev), err)
 		}
 	}()
 	if twoSrc {
@@ -170,7 +170,7 @@ func (r *Recorder) Start(fromDev, micDev string, prerollSec int) error {
 				r.lastB = time.Now()
 				r.srcMu.Unlock()
 			}); err != nil {
-				LogSink("recorder: capture from %q failed: %v", micDev, err)
+				LogSink("recorder: capture from %q failed: %v", DeviceName(micDev), err)
 			}
 		}()
 	}
@@ -193,11 +193,11 @@ func (r *Recorder) Start(fromDev, micDev string, prerollSec int) error {
 		aQuiet, bQuiet := r.lastA.IsZero(), r.lastB.IsZero()
 		r.srcMu.Unlock()
 		if aQuiet {
-			LogSink("recorder: no audio at all from %q after 3 s — the device opened but nothing is streaming", fromDev)
-			AlertSink("No audio from %s — nothing is being recorded", fromDev)
+			LogSink("recorder: no audio at all from %q after 3 s — the device opened but nothing is streaming", DeviceName(fromDev))
+			AlertSink("No audio from %s — nothing is being recorded", DeviceName(fromDev))
 		}
 		if twoSrc && bQuiet {
-			LogSink("recorder: no audio at all from %q after 3 s — the device opened but nothing is streaming", micDev)
+			LogSink("recorder: no audio at all from %q after 3 s — the device opened but nothing is streaming", DeviceName(micDev))
 		}
 	}()