Fail fast when configured recording input cannot be resolved

src/recorder.py

@@ -36,12 +36,17 @@ def resolve_input_device(spec: str | int | None) -> int | None:
     if spec is None:
         return None
     if isinstance(spec, int):
-        return spec
+        if _input_device_exists(spec):
+            return spec
+        return None
     text = str(spec).strip()
     if not text:
         return None
     if text.isdigit():
-        return int(text)
+        device_idx = int(text)
+        if _input_device_exists(device_idx):
+            return device_idx
+        return None
     lowered = text.lower()
     for device in list_input_devices():
         name = (device.get("name") or "").lower()
@@ -54,6 +59,11 @@ def start_recording(input_spec: str | int | None) -> tuple[Any, RecordResult]:
     sd = _sounddevice()
     record = RecordResult()
     device = resolve_input_device(input_spec)
+    if _is_explicit_input_spec(input_spec) and device is None:
+        raise ValueError(
+            f"recording.input '{input_spec}' did not match any input device; "
+            f"available inputs: {_available_input_devices_summary()}"
+        )
 
     def callback(indata, _frames, _time, _status):
         record.frames.append(indata.copy())
@@ -105,3 +115,28 @@ def _flatten_frames(frames: Iterable[np.ndarray]) -> np.ndarray:
     if data.ndim > 1:
         data = np.squeeze(data, axis=-1)
     return np.asarray(data, dtype=np.float32).reshape(-1)
+
+
+def _input_device_exists(device_idx: int) -> bool:
+    for device in list_input_devices():
+        if int(device.get("index", -1)) == int(device_idx):
+            return True
+    return False
+
+
+def _is_explicit_input_spec(input_spec: str | int | None) -> bool:
+    if input_spec is None:
+        return False
+    if isinstance(input_spec, int):
+        return True
+    return bool(str(input_spec).strip())
+
+
+def _available_input_devices_summary(limit: int = 8) -> str:
+    devices = list_input_devices()
+    if not devices:
+        return "<none>"
+    items = [f"{d['index']}:{d['name']}" for d in devices[:limit]]
+    if len(devices) > limit:
+        items.append("...")
+    return ", ".join(items)