Fix DOCKERDISC_HOST_MAC docs and strengthen case-insensitivity test

resolve_host_mac() returns the manually configured MAC immediately,
with no Socket Proxy /info call at all - the config.json text still
described it as a fallback used only when auto-detection fails.
Reworded both the setting's own description and the parent "Docker
hosts" description to match actual behavior.

The case-insensitivity regression test for lookup_device_mac() stubbed
DeviceInstance.getByMac() to return a fixed row regardless of input,
so it passed even without exercising real collation - functionally a
duplicate of test_lookup_device_mac_found. Replaced it with a
delegation check, and added real SQLite-backed coverage for
DeviceInstance.getByMac()'s case-insensitivity in
test/backend/test_device_instance.py. That surfaced a gap in the
shared db_test_helpers.py fixture: its Devices.devMac column was
missing the COLLATE NOCASE that the real schema declares, so it could
not have exercised this behavior. Fixed the fixture to match.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011meLPKCzVpdZyAUfv5U6mm

test/plugins/test_dockerdisc.py

@@ -445,20 +445,18 @@ def test_lookup_device_mac_not_found():
         assert dockerdisc.lookup_device_mac("aa:bb:cc:dd:ee:ff") is False
 
 
-def test_lookup_device_mac_found_regardless_of_stored_mac_case():
-    """The plugin always passes a lowercase, normalize_mac()'d value in -
-    this only guards that lookup_device_mac() doesn't do anything of its
-    own (e.g. an exact-string comparison) that would undo whatever
-    case-insensitivity DeviceInstance.getByMac() provides. The real
-    guarantee is schema-level - Devices.devMac is declared
-    `COLLATE NOCASE` (server/db/schema/app.sql), which is exactly why
-    getByMac() itself doesn't need to apply it explicitly (unlike
-    getAllByName(), which does - devName has no such column collation;
-    see that method's docstring and test/backend/test_device_instance.py).
-    This test's stub can't exercise real SQLite collation, only that this
-    function's own logic is agnostic to it."""
-    with patch.object(dockerdisc, "DeviceInstance", _stub_device_instance(get_by_mac={"devMac": "AA:BB:CC:DD:EE:FF"})):
-        assert dockerdisc.lookup_device_mac("aa:bb:cc:dd:ee:ff") is True
+def test_lookup_device_mac_passes_mac_through_unchanged():
+    """lookup_device_mac() must not do any of its own case massaging - it
+    delegates entirely to DeviceInstance.getByMac(), which relies on
+    Devices.devMac's schema-level `COLLATE NOCASE` (server/db/schema/app.sql)
+    for case-insensitive matching. That guarantee is exercised against a
+    real SQLite connection in test/backend/test_device_instance.py's
+    TestGetByMac; a mocked DeviceInstance can't exercise real collation, so
+    this test only checks that the mac argument reaches getByMac() as-is."""
+    stub = _stub_device_instance(get_by_mac={"devMac": "aa:bb:cc:dd:ee:ff"})
+    with patch.object(dockerdisc, "DeviceInstance", stub):
+        dockerdisc.lookup_device_mac("AA:BB:CC:DD:EE:FF")
+    stub.return_value.getByMac.assert_called_once_with("AA:BB:CC:DD:EE:FF")
 
 
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