fix(wake): auto capture keeps the backend mic when one exists

With capture:auto the desktop always preferred client streaming, so a local
desktop with a working backend mic silently switched from PortAudio to
getUserMedia default-device — dropping wake_word.input_device selection
(#74363). A ready backend input now wins under auto; client capture is the
fallback for a preferring surface on a mic-less backend, and capture:client
still forces streaming.

Also removes the dead auto branch (both arms returned local) and lets the
client-feed test skip cleanly when numpy is absent.

tests/tools/test_wake_word.py

@@ -641,7 +641,11 @@ def test_resolve_capture_mode_auto_and_prefer_client(monkeypatch):
     assert ww.resolve_capture_mode({"capture": "auto"}, force_local=True) == "local"
     monkeypatch.setattr(ww, "_local_input_device_ready", lambda: True)
     assert ww.resolve_capture_mode({"capture": "auto"}) == "local"
-    assert ww.resolve_capture_mode({"capture": "auto"}, prefer_client=True) == "client"
+    # A working backend mic wins under auto even for a preferring surface, so
+    # local desktops keep PortAudio + wake_word.input_device selection.
+    assert ww.resolve_capture_mode({"capture": "auto"}, prefer_client=True) == "local"
+    # Explicit client still forces streaming (backend mic exists but is wrong).
+    assert ww.resolve_capture_mode({"capture": "client"}, prefer_client=True) == "client"
 
 
 def test_requirements_client_capture_without_local_mic(monkeypatch):
@@ -674,7 +678,7 @@ def test_requirements_client_capture_without_local_mic(monkeypatch):
 
 
 def test_client_capture_feed_fires(monkeypatch, tmp_path):
-    import numpy as np
+    np = pytest.importorskip("numpy")
 
     monkeypatch.setattr(ww, "_build_engine", lambda cfg: _FakeEngine(fire=True))
     monkeypatch.setattr(ww, "_lock_path", lambda: tmp_path / "wake.lock")

tools/wake_word.py

@@ -269,15 +269,17 @@ def resolve_capture_mode(
         return "client"
     if raw == "local":
         return "local"
-    # auto
-    if prefer_client:
-        return "client"
-    # Prefer local when a PortAudio input exists. Without an explicit client
-    # preference (desktop remote), stay on local so CLI/TUI/status still
-    # require a server mic instead of advertising a capture path only the
-    # desktop can feed.
+    # auto: a working backend input always wins so local desktops keep
+    # PortAudio and the configured ``input_device`` selection. Client capture
+    # is the fallback for a preferring surface (desktop remote) on a backend
+    # with no usable mic — the headless VPS/Cloud case.
     if _local_input_device_ready():
         return "local"
+    if prefer_client:
+        return "client"
+    # No local mic and no client preference (CLI/TUI): stay local so status
+    # reports the real requirement instead of advertising a capture path
+    # nothing will feed.
     return "local"